Methods for Sampling and 

Inorganic Analysis of Coal 

U.S. GEOLOGICAL SURVEY BULLETIN 1823 ° 
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Methods for Sampling and 

Inorganic Analysis of Coal 

Edited by D.W. GOLIGHTLY and F.O. SIMON 

This manual presents a collection of detailed procedures used 

in geochemical laboratories of the U.S. Geological Survey for 

the chemical characterization of coal. 

U.S. GEOLOGICAL SURVEY BULLETIN 1823 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade names and trademarks 

in this publication is for descriptive 

purposes only and does not constitute 

endorsement by the U.S. Geological Survey 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989 

For sale by the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Methods for sampling and inorganic analysis of coal. 

(U.S. Geological Survey bulletin ; 1823) 

Includes bibliographies. 

Supt. of Docs. no.: I 19.3:1823 

1. Coal-Sampling. 2. Coal-Analysis. I. Golightly, D.W. II. Simon, Frederick Otto, 1939- . Ill. Series. 

QE75.B9 no. 1823 557.3 s [662.6'22] 87-600439 

[TP325] 
CONTENTS 

Methods for Sampling and Inorganic Analysis of Coal-Introduction 

By D.W. Golightly and F.O. Simon 

Abstract 1 

Introduction 1 

References 3 

Sampling of Coal Beds for Analysis 

By R.W. Stanton 

Abstract 7 

Purposes of sampling a coal bed 7 

Historical perspective of sampling 8 

Sampling for rank classification 8 

Sampling for chemical analysis 9 

Sampling for other purposes 9 

Procedure for channel sampling 9 

Procedure for sampling drill core 9 

Coal bed descriptions 10 

Identification of carbonaceous shale layers 11 

Sampling thick coal beds 11 

Summary 11 

References 13 

Preparation of Coal for Analysis 

By F.G. Walthall and S.L. Fleming, II 

Abstract 15 

Introduction 15 

Equipment and procedures 15 

Sample preparation (grinding) laboratory- equipment 15 

Safety equipment and provisions 16 

Safety procedures 16 

Maintenance of equipment 16 

Sample preparation (grinding) laboratory- facilities 16 

Crushing and grinding 16 

Description of procedure 17 

Ashing procedure 18 

Cleaning of work area and equipment 18 

References 19 

Automated Semiquantitative Direct-Current Arc Spectrographic Determination of 

64 Elements in Coal Ash 

By A.F. Dorrzapf, Jr., C.J. Skeen, and W.B. Crandell 

Abstract 21 

Introduction 21 

The method 21 

Exposure procedure 21 

Contents iii 
iv Contents 

The scanning microphotometer system 21 

The minicomputer configuration 22 

Data handling 23 

Wavelength calibration 23 

Concentration calibration 23 

Spectral-interference corrections 23 

Plate emulsion calibration 23 

Quality control 25 

Conclusions 25 

References 25 

The Determination of 41 Elements in Whole Coal by Instrumental Neutron 

Activation Analysis 

By C.A. Palmer and P.A. Baedecker 

Abstract 27 

Introduction 27 

Activation analysis 27 

Experimental methods and procedures 28 

Sample preparation 28 

Standards 28 

Counting facilities 30 

Data reduction 30 

Quality control 32 

Discussion 32 

References 34 

The Determination of Major and Minor Elements in Coal Ash and of Chlorine and 

Phosphorus in Whole Coal by X-Ray Fluorescence Spectrometry 

By R.G. Johnson, G.A. Sellers, and S.L. Fleming, II 

Abstract 35 

Introduction 35 

Experimental methods and procedures 35 

Equipment and supplies 35 

Coal ash 36 

Whole coal 37 

Conclusions 38 

References 38 

Analysis of Coal Ash by Atomic Absorption Spectrometric and 

Spectrophotometric Methods 

By F.W. Brown and Hezekiah Smith 

Abstract 41 

Introduction 41 

Spectrophotometric procedures 41 

Atomic absorption spectrometric methods 42 

Precision of analysis 42 

Preparation of sample solution 42 

Reagents and supplies 42 

Procedure 42 

Determination of silicon (as Si02) 43 

Reagents and equipment 43 

Procedure 43 
Determination of aluminum (as Al20 3) 43 

Reagents, supplies, and equipment 43 

Procedure 43 

Determination of phosphorus (as P 20 5) 44 

Reagents and equipment 44 

Procedure 44 

Determination of titanium (as Ti02) 44 

Reagents and equipment 44 

Procedure 44 

Determination of calcium, iron, magnesium, manganese, potassium, 

and sodium 44 

Reagents and equipment 44 

Procedure for calcium, iron, magnesium, and manganese 45 

Procedure for potassium and sodium 45 

Conclusions 45 

References 45 

The Determination of Selected Elements in Coal Ash by Atomic Absorption 

Spectrometry 

By J.S. Kane 

Abstract 47 

Introduction 47 

Experimental methods and procedures 47 

Dissolution of samples 47 

Cadmium extraction 47 

Calibration solutions 48 

Instrumentation 48 

Discussion of results 49 

Manganese 50 

Lead 51 

Zinc 51 

Copper 51 

Lithium 51 

Sodium 52 

Magnesium 52 

Cadmium 52 

References 53 

The Determination of Mercury in Whole Coal by Cold-Vapor Atomic Absorption 

Spectrometry 

By P.J. Aruscavage and Roosevelt Moore 

Abstract 55 

Introduction 55 

Experimental equipment and methods 56 

Equipment 56 

Reagents 56 

Calibration standards 56 

Coal standards 56 

Procedures 56 

Dissolution of samples 56 

Determination of mercury 56 

Discussion 57 

References 57 

Contents v 
vi Contents 

The Determination of Fluoride in Coal by !on-Selective Electrode 

By Herbert Kirschenbaum 

Abstract 59 

Introduction 59 

Experimental methods and procedures 59 

Equipment 59 

Reagents 59 

Procedure 60 

Accuracy, precision, and detectability 61 

References 61 

The Determination of Forms of Sulfur in Coal 

By Norma Rait and P.J. Aruscavage 

Abstract 63 

Introduction 63 

Experimental equipment and methods 63 

Sample requirements 63 

Laboratory, supplies, and equipment 63 

Methods 65 

Total sulfur 65 

Laboratory setup for the separation of forms of sulfur 65 

Monosulfide sulfur separation and determination 65 

Sulfate sulfur separation and determination 65 

Pyritic sulfur separation and determination 66 

Calculation of organically bound sulfur 66 

Discussion 66 

References 68 

Appendix: Reference Materials for Coal Analysis 

By D.W. Golightly and F.O. Simon 

Sulfur in coal: NBS standards 2682 through 2685 69 

Trace mercury in coal: NBS standard 1630 69 

Concentrations of elements in NBS-SRM coals and coal fly ash 69 

MINTEK coal standards: South African reference materials 70 

BCR reference materials 71 

CRM 065 coal 71 

CRM 038 fly ash from pulverized coal 71 

Premium coal sample program, Argonne National Laboratory 71 

Coal and coal-ash standards for trace elements and radioactivity, 

International Atomic Energy Agency 71 

Trace metals in coal, Alpha Resources, Inc. 71 

U.S. Geological Survey coal standard: preliminary data for whole coal 72 

FIGURES 

1. Flowchart for samples and analyses of coals 3 

2. Correlation of facies of a single coal bed 8 

3. Natural gamma and high-resolution density logs of a coal bed showing log 

responses of coal and imp: -e coal or parting 10 

4. Container for collection of core samples 10 

5. Example of description of generalized stratigraphic section of 

the Upper Freeport coal bed 11 
6. Ash yields of 134 facies samples of the Upper Freeport 

coal bed 11 

7. X-ray radiograph of an undisturbed coal core showing mineral impurities 

and coal lithotype layers 12 

8. Sample preparation laboratories 17 

9. Sample preparation procedure for coals 17 

10. Splitting procedure 18 

11. Spectrum of NBS coal standard 1632 collected 5 days after irradiation 28 

12. Lead absorbance as a function of iron concentration in the sample 

matrix 51 

13. Zinc correlation plot 52 

14. Diagram of arrangement of instrumentation for the measurement of mercury 

in coal 56 

15. Two typical calibration curves 60 

16. Flowchart for the separation of the forms of sulfur 64 

17. Photograph of setup 64 

18. Diagrams of apparatus 64 

TABLES 

1. Lower determination limits for elements in coal or coal ash, listed by method 

of analysis 2 · 

2. Selected ASTM standard methods 4 

3. Types of samples and purposes for which samples are commonly 

collected 7 

4. Instrumentation and operating conditions 22 

5. Spectral lines used in spectrographic analysis, listed in order of decreasing 

intensity 24 

6. Direct current arc spectrographic analyses of NBS standard reference 

material coal fly ash 26 

7. Long-lived (> 10 h) radionuclides 29 

8. Short-lived indicator radionuclides 30 

9. Concentrations of 40 elements in multiple-element standards 

used for the analysis of coal 31 

10. Interferences in INAA due to neutron-induced fission of 235U 32 

11. Instrumental operating conditions for XRF analysis of coal ash 36 

12. Concentration ranges provided by rock standards for the XRF analysis of 

coal ash 36 

13. XRF calibration of iron in coal ash: simple linear regression analysis 

results 37 

14. Operating conditions for XRF analysis of whole coal 37 

15. XRF calibration of P20 5 in whole coal: simple linear regression analysis 

results 38 

16. Operating conditions for atomic absorption spectrometry 42 

17. Estimated precision of analysis 42 

18. Compositions of coal ashes determined by methods based on atomic 

absorption spectrometry (AAS) or spectrophotometry and on X-ray 

fluorescence (XRF) spectrometry 46 

19. Operating parameters: flame and graphite-furnace atomization 48 

20. Detection limits, sensitivities, and calibration ranges for flame and 

graphite-furnace atomic absorption spectrometry 49 

Contents vii 
viii Contents 

21. Alternate operating parameters for flame atomic absorption spectrometry and 

calibration ranges 49 

22. Concentrations of eight elements in the NBS 1633 coal fly ash determined by 

atomic absorption spectrometric methods 50 

23. Concentrations of analytes determined for NBS standard reference material 

1633a and for quality-control samples 50 

24. Some typical concentration ranges of analytes in coal ashes originating from 

different regions of the United States 53 

25. Concentrations of mercury determined by cold-vapor atomic absorption 

spectrometry for selected coal and fly-ash standards 57 

26. Dilutions for preparation of individual calibration standards 60 

27. Total sulfur in coal 66 

28. Monosulfide sulfur in coal 67 

29. Sulfate sulfur in coal 67 

30. Pyritic sulfur in coal 67 

31. Pyritic sulfur in coal by direct method 67 

32. Organically bound sulfur in coal by direct method 68 

33. Organically bound sulfur in coal by indirect method 68 

ACRONYMS 

AAS 

AES 

AFT 

ASTM 

BCR 

CAL 

CRM 

FSI 

HGI 

ICP 

INAA 

ISA 

ISE 

LOI 

MINTEK 

NBS 

NCRDS 

PVC 

RSD 

SARM 

SPGR 

SRM 

TRIG A 

USCHEM 

USGS 

WDXRF 

XRF 

atomic absorption spectrometry 

atomic emission spectrography (or spectrometry) 

ash fusion temperature 

American Society for Testing and Materials 

Community Bureau of Reference (Commission of the European 

Communities, Brussels) 

calorific value 

certified reference material (BCR) 

free swelling index 

Hardgrove grindability index 

inductively coupled plasma 

instrumental neutron activation analysis 

infrared spectrometric sulfur analyzer 

ion selective electrode 

loss on ignition 

Council for Mineral Technology, South Africa 

National Bureau of Standards 

National Coal Resources Data System (USGS) 

polyvinylchloride 

relative standard deviation 

South African reference material (MINTEK) 

specific gravity 

standard reference material (NBS) 

thermal reactor installation-General Atomic [Company] 

United States Chemistry data base within NCRDS 

United States Geological Survey 

wavelength dispersive x-ray fluorescence 

x-ray fluorescence 
Methods for Sampling and 

Inorganic Analysis of Coal 

INTRODUCTION 

By D.W. Golightly and F.O. Simon 

Abstract 

Methods used by the U.S. Geological Survey for the 

sampling, comminution, and inorganic analysis of coal are 

summarized in this bulletin. Details, capabilities, and limitations of the methods are presented. 

INTRODUCTION 

The large body of chemical information (for 

example, see Averitt and Lopez, 1972; O'Gorman and 

Walker, 1972; Zubovic and others, 1980) available to the 

modern coal scientist has been provided by diverse 

instrumental and chemical methods of analysis. The 

methods used in U.S. Geological Survey laboratories 

(Golightly and others, 1986; Simon and Huffman, 1978; 

Swanson and Huffman, 1976) change with the requirements for investigations of coal composition and with 

refinements in the instrumentation and approaches to 

chemical analysis. Detailed descriptions of most of the 

methods routinely used in U.S. Geological Survey laboratories for determining the inorganic composition of 

coal are provided in this bulletin. In addition to the 

descriptions of methods, one section is dedicated to the 

important topic of coal sampling and another treats the 

comminution of field samples prior to analysis. 

Concentrations of more than 70 elements important to investigations of coal are determined by diverse 

methods established for the chemical and instrumental 

analysis of both whole coal and coal ash. This diversity 

results from the different capabilities of the individual 

methods, the quality of information sought, and the 

cost of this information. The measurement techniques 

used for the determination of major, minor, and trace 

elements in coal and coal ash include atomic emission 

spectrography (AES), atomic absorption spectrometry 

(AAS), X-ray fluorescence (XRF) spectrometry, instrumental neutron activation analysis (INAA), and ionselective electrode (ISE). The conventional routing of 

samples and types of analyses are illustrated by the chart 

in figure 1. 

For the routine quantitative analysis of coal ash 

(ashing temperature of 525 °C), the elements Cd, Cu, 

Li, Mg, Mn, Na, Pb, and Zn are determined by AAS, 

and AI, Ca, Fe, K, Mg, Mn, Na, P, S, Si, and Ti are 

determined by XRF spectrometry. Rapid chemical methods, described in this bulletin, offer an alternative 

approach for measurements of the same elements determined by XRF spectrometry. After a special ashing 

procedure and fusion of the resulting ash with NaOH, 

fluorine concentrations are measured by ISE. An automated, semiquantitative direct-current (de) arc AES 

method is applied to the analysis of all coal ashes for the 

determination of 64 elements. Lower determination 

limits for the methods used for the analysis of coal ash 

are listed in table 1. 

For the routine quantitative analysis of whole 

coal, Hg is determined by cold-vapor AAS; Cl and Pare 

measured by XRF spectrometry; and As, Ba, Br, Ce, 

Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Lu, Na, Nd, Rb, Sb, 

Sc, Se, Sm, Sr, Ta, Tb, Th, U, W, Yb, and Zn are 

determined by INAA. Total sulfur and sulfur species 

(forms of sulfur) are determined by gas-phase infrared 

absorption spectrometry that is combined with chemical 

separation methods. Lower determination limits for 

these methods are summarized in table 1. 

In addition to analyzing coal for the elements 

indicated in table 1, the U.S. Geological Survey routinely analyzes coals by methods recommended by the 

American Society for Testing and Materials (ASTM) for 

calorific value, proximate analysis (moisture, ash, volatile matter, and fixed carbon), ultimate analysis (C, H, 

N, 0, and S), and physical parameters, such as Hardgrove grindability, ash-fusion temperature, specific gravity, and free-swelling index. Equilibrium moisture is 

determined on selected samples. The "1984 Annual 

Book of ASTM Standards" (ASTM, 1984) provides 

Introduction 
I>.) 

s: 

!l 

::r 

0 

c.. 

"' 

~ Ill 

11.1 

3 

'E. 

:;· 

()Q 

11.1 

::l 

c.. 

::l 

s; 

()Q 

11.1 

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Table 1. Lower determination limits (in p,g/g) for elements in whole coal or coal ash, listed by method of analysis 

H 

Li 2 Be 

68 1 

Na 1 Mg 1 

100 100 

10 

22 22 

K Ca Sc 

100 100 

100 

680 10 

Rb Sr y 

5 50 

1 

Cs Ba La 

0.1 100 

1.5 

Fr Ra Ac 

- ---- --

Key: 

Element 

Ti 

100 

0.01 

1 32 

Zr 

100 

1.5 3 

Hf 

0.02 0.1 

10 15 

Ce 

0.5 

43 

Th 

0.1 

46 

Na AAS 

XRF 

INAA 

DCA 

B 

AI 

v Cr Mn 2 Fe Co Ni Cu 10 Zn 1 Ga 

100 100 

1 1 100 0.2 500 1 

1 1 1 74 1 1.5 1 10 

Nb Mo Tc Ru Rh Pd Ag Cd .02 

10 

7 1 2 2 1 0.1 32 

Ta w Re Os Ir Pt Au Hg .01 

CVAAS 

0.03 0.1 0.01 0.005 1 

320 15 10 15 15 2 7 

Pr Nd Pm Sm Eu Gd Tb Dy 

2 0.5 0.02 2 0.1 

100 32 10 2 32 32 

Pa u Np Pu Am Cm Bk Cf 

0.5 

220 

Lower determination limit, p,g/g, in the coal or coal ash measured by: 

Atomic Absorption Spectrometry [ash], Hg by Cold-Vapor AAS [whole coal]; 

X-Ray Fluorescence spectrometry [ash, whole coal]; 

Instrumental Neutron Activation Analysis [whole coal]; 

Direct-Current Arc spectrography, semiquantitative [ash]. 

ISE: Ion-Selective Electrode (fluorine only). 

In 

Tl 

10 

22 

He I 

I 

I 

c N 0 F 20 Ne 

I 

ISE 

3 I 

Si p s Cl Ar I 

100 500 100 100 100 I 

460 46 680 I 

Ge As Se Br Kr I 

I 5 1 1 1 

1.5 5 100 I 

Sn Sb Te I Xe 

I 

0.1 

I 

10 5 68 

Pb 20 Bi Po At Rn 

10 7 10 

Ho Er Tm Yb Lu 

0.5 0.5 0.2 0.01 

7 5 5 0.2 15 

Es Fm Md No Lw 

I 
FIELD SAMPLE 

(3 to 15 kg) 

I 

RECORDS 

(Data base, Labels. Routing) 

PREPARATION 

(Grinding, Splitting, Ashing) 

Delayed INAA ISA 

Neutron [29) [S) 

[U, Th) 

Proximate Analysis 

[ Moisture, Volatile Matter, 

Fixed Carbon, Ash] 

AAS XRF ISE 

[Hg) [CI,P] [F) 

ASH 

I XRF + AAS AES 

Ultimate 

Analysis 

[C. H. N, 0, S] 

I 

Physical Tests 

[FSI, HGI, AFT, SPGR, CAL] 

AAS :atomic absorption spectrometry 

AES :optical emission spectrography 

AFT : ash fusion temperature 

CAL : calorific value 

FSI :free-swelling index 

[10) [8) [64) 

HGI :Hardgrove grindability index 

INAA : instrumental neutron activation analysis 

ISA :infrared spectrometric sulfur analyzer 

ISE : ion-selective electrode 

SPGR: Specific gravity 

XRF :x-ray fluorescence spectrometry 

[) :square brackets indicate the property 

measured, the elements determined, or 

the number of elements determined. 

Figure 1. Flowchart for samples and analyses of coals. 

detailed descriptions of the standard procedures used. A 

list of the pertinent ASTM methods appears in table 2. 

All data for coals and associated rocks analyzed 

by the U.S. Geological Survey reside in the National 

Coal Resources Data System (NCRDS) (Carter and 

others, 1981). The NCRDS is an interactive computerized storage, retrieval, and display system created to 

assess the quantity and quality of the nation's coal 

resources. Currently, the NCRDS USCHEM data bases 

contain analytical data on approximately 10,000 pointlocated coal and associated rock samples from all coal 

regions of the United States. Other data bases contain 

information on approximately 50,000 samples that are 

area located. In addition, the geochemical data bases 

contain geologic and geographic data for each sample. 

A total of 128 parameters, including the analytical data, 

can be stored for each sample. The geologic and geographic data include State, county, latitude, longitude, 

coal province, region, coal field, district, formation 

group, coal bed, member, zone, series, location name, 

quadrangle, collector, point identification, date, estimated rank, calculated rank, laboratory identification 

number, and sample type. 

The accuracy of analysis by the U.S. Geological 

Survey methods, each of which is the topic of a section 

of this bulletin, is ultimately linked to a standard 

reference material (Uriano and Gravatt, 1977). These 

standard coals and coal ashes are provided by various 

agencies, such as the National Bureau of Standards, and 

commercial laboratories, such as Alpha Resources, Inc. 

Representative materials are described in the appendix 

to this bulletin, where the addresses of suppliers are also 

given. A significant new development is underway at the 

Argonne National Laboratory where eight premium 

coal standards are being prepared (see the appendix). 

In addition to this bulletin, a large body of 

information on the chemical and physical characterizations of coal is available to the coal scientist. The general 

methodologies used for inorganic analysis of coal, critically reviewed recently by Swaine (1985) for bituminous 

coal, are described in various journal articles and books. 

Valkovic ( 1983) has provided a comprehensive review of 

both the chemistry and the methodology used for the 

characterization of coal. Mills and Belcher (1981) surveyed atomic spectrometric methods for the analysis of 

coal, coke, ash, and mineral matter. The "1984 Annual 

Book of ASTM Standards" (ASTM, 1984) provides 

detailed descriptions of standard procedures for sampling, grinding, and analyzing coal and coke. Volumes 

edited by Babu (1975) and Karr (1978) describe numerous instrumental and chemical methods for the characterization of coal. Mineral matter and trace-element 

associations are treated in these two books and in a 

recently published book by Vorres (1986). 

REFERENCES 

American Society for Testing and Materials (ASTM), 1984, 

annual book of ASTM standards, petroleum products, 

lubricants, and fossil fuels, sect. 5 of v. 05.05: Gaseous 

fuels, coal, and coke: Philadelphia, ASTM, p. 207-523. 

Averitt, Paul, and Lopez, Lorreda, 1972, Bibliography and 

index of U.S. Geological Survey publications relating to 

coal, 1882-1970: U.S. Geological Survey Bulletin 1377, 

173 p. 

Babu, S.P ., ed., 1975, Trace elements in fuel, in Advances in 

chemistry series 141: Washington, D.C., American Chemical Society, 216 p. 

Carter, M.D., Medlin, A.L., and Krohn, K.K., 1981, The 

national coal resources data system: a status report: 

Geological Society of America Bulletin, v. 92, pt. 1, p. 

563-573. 

Golightly, D.W., Dorrzapf, A.F., Jr., Larson, R.R., Aruscavage, P.J., and Palmer, C.A., 1986, Current analytical 

methods for determining the inorganic composition of 

coal, in Garbini, Susan, and Schweinfurth, S.P., eds., A 

National Agenda for Coal-Quality Research, April 9-11, 

1985 Symposium Proceedings: U.S. Geological Survey 

Circular 979, p. 232. 

Introduction 3 
Table 2. Selected ASTM standard methods (ASTM, 1984) 

Designation 

D121-78(1983) 

D167-73(1979) 

D388-82 

D409-71(1978) 

D-720-83 

D1412-74(1979) 

D1757-80 

D1857-68(1980) 

D2013-72(1978) 

D2015-77(1978) 

D2234-82 

D2361-83 

D2492-84 

D2795-84 

D2796-82 

D3172-73(1979) 

D3173-73( 1979) 

D3174-82 

D3175-82 

D3176-84 

D3177-84 

D3178-84 

D3179-84 

D3180-84 

D3286-82 

D3302-82 

D3682-78(1983) 

D3683-78(1983) 

D3684-78( 1983) 

D3761-79(1984) 

D4208-83 

D4239-83 

D4326-84 

D4182-82 

Title 

Standard Definitions of Terms Relating to Coal and Coke, p. 207-208. 

Standard Test Method for Specific Gravity and Porosity of Lump Coke, p. 209-212. 

Standard Classification of Coals by Rank, p. 242-246. 

Standard Test Method for Grindability of Coal by the Hargrove-Machine Method, p. 247-253. 

Standard Test Method for Free-Swelling Index of Coal, p. 272-278. 

Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 percent Relative Humidity and 

30° C, p. 279-281. 

Standard Test Methods for Sulfur in Ash from Coal and Coke, p. 286-290. 

Standard Test Method for Fusibility of Coal and Coke Ash, p. 292-297. 

Standard Method of Preparing Coal Samples for Analysis, p. 298-312. 

Standard Test Method for Gross Calorific Value of Solid Fuel by the Adiabatic Bomb Calorimeter, p. 

320-328. 

Standard Methods for Collection of a Gross Sample of Coal, p. 329-345. 

Standard Test Method for Chlorine in Coal, p. 346-349. 

Standard Test Methods for Forms of Sulfur in Coal, p. 350-354. 

Standard Methods of Analysis of Coal and Coke Ash, p. 366-373. 

Standard Definitions of Terms Relating to Megascopic Description of Coal and Coal Seams and 

Microscopical Description and Analysis of Coal, p. 374-377. 

Standard Method for Proximate Analysis of Coal and Coke [moisture, volatile matter, fixed carbon 

(by difference), and ash], p.397. 

Standard Test Method for Moisture in the Analysis Sample of Coal and Coke, p. 398-400. 

Standard Test Method for Ash in the Analysis Sample of Coal and Coke From Coal, p. 401-404. 

Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke, p. 405-408. 

Standard Method for Ultimate Analysis of Coal and Coke [C,H,S,N,O,Ash], p. 409-412. 

Standard Test Methods for Total Sulfur in the Analysis Sample of Coal and Coke, p. 413-417. 

Standard Test Methods for Carbon and Hydrogen in the Analysis Sample of Coal and Coke, p. 

418-423. 

Standard Test Methods for Nitrogen in the Analysis Sample of Coal and Coke, p. 424-430. 

Standard Test Method for Calculating Coal and Coal Analysis from the As-Determined to Different 

Bases, p. 431-434. 

Standard Test Method for Gross Calorific Value of Solid Fuel by the Isothermal-jacket Bomb 

Calorimeter, p. 435-444. 

Standard Test Method for Total Moisture in Coal, p. 445-454. 

Standard Test Methods for Major and Minor Elements in Coal and Coke Ash by Atomic Absorption 

[Si,Al,Fe,Ca,Mg,Na,K,Ti,Mn,P] p. 458-465. 

Standard Test Method for Trace Elements in Coal and Coke Ash by Atomic Absorption [Be,Cd,Cr, 

Cu,Mn,Ni,Pb,V,Zn], p. 466-469. 

Standard Test Method for Total Mercury in coal by the Oxygen Bomb Combustion - Atomic 

Absorption Method, p. 470-473. 

Standard Test Method for Total Fluorine by the Oxygen Bomb Combustion - Ion Selective Electrode 

Method, p. 474-477. 

Standard Test Method for Total Chlorine in Coal by the Oxygen Bomb Combustion - Selective Ion 

Electrode Method, p. 480-483. 

Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke using High Temperature 

Tube Furnace Combustion Methods, p. 484-495. 

Standard Test Method for Major and Minor Elements in Coal and Coke Ash by X-Ray Fluorescence, 

p. 496-499. 

Standard Practice for Evaluation of Laboratories using ASTM Procedures in the Sampling and 

Analysis of Coal and Coke, p. 478-479. 

4 Methods for Sampling and Inorganic Analysis of Coal 
Karr, Clarence, ed., 1978, Analytical methods for coal and 

coke products, v. 1-3: New York, Academic Press. 

Mills, J.C., and Belcher, C.B., 1981, Analysis of coal, coke, 

ash, and mineral matter by atomic spectroscopy: Progress 

in Analytical Atomic Spectroscopy, v. 4, p. 49-80. 

O'Gorman, J.V., and Walker, P.L., 1972, Mineral matter and 

trace elements in U.S. coals: Washington, D.C., U.S. 

Government Printing Office, 183 p. 

Simon, F.O., and Huffman, Claude, Jr., 1978, Analytical 

methods used by the U.S. Geological Survey for determining the composition of coal: Paper no. 82, Meeting of 

the American Chemical Society, 173rd, New Orleans, 

March 20-25. 

Swaine, D .J., 1985, Modern methods in bituminous coal 

analysis: Trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 315-346. 

Swanson, V.E., and Huffman, Claude, Jr., 1976, Guidelines 

for sample collecting and analytical methods used in the 

U.S. Geological Survey for determining chemical composition of coal: U.S. Geological Survey Circular 735, 11 p. 

Uriano, G.A., and Gravatt, C. C., 1977, The role of reference 

materials and reference methods in chemical analysis: 

CRC Critical Reviews in Analytical Chemistry, v. 6, p. 

361-411. 

Valkovic, Vlado, 1983, Trace elements in coal, v. I, II: CRC 

Press, Boca Raton, Florida, 491 p. 

Vorres, K.S., ed., 1986, Mineral matter and ash in coal, in 

American Chemical Society symposium series no. 301: 

Washington, D.C., American Chemical Society, p. 538. 

Zubovic, Peter, Oman, C.L., Bragg, L.J., Coleman, S.L., 

Rega, N.H., Lemaster, M.E., Rose, H.J., Golightly, 

D.W., and Puskas, John, 1980, Chemical analysis of 659 

coal samples from the eastern United States: U.S. Geological Survey Open-File Report 80-2003, 513 p. 

Introduction 5 

Si\MPLING OF COAL BEDS FOR ANALYSIS 

By Ronald W. Stanton 

Abstract 

Channel and core samples are the primary types of 

samples collected and analyzed to establish the chemical 

composition, or quality, of coal beds. The choice between 

channel or core samples may be predicated on cost and 

accessibility to the coal bed. The purpose of the investigation 

or program determines the nature of the sample to be taken 

and the materials to be included in the sample. Impurities, 

such as mineral-rich layers, may be included in the sample, 

depending on the intended use of the data. 

A channel or core sample should (1) represent an equal 

volume from the top to the bottom of the coal bed and (2) 

experience minimal comminution and (3) not be split in the 

field. Discrimination between impure coal, carbonaceous 

shale, and coal sometimes is subjective and consequently 

affects the precision of the sampling method. A coal bed can 

be described and sampled by facies by delimiting the laterally 

continuous subunits of the bed and by evaluating their effect 

on bed quality, particularly in the collection of channel samples. Descriptions of core samples are facilitated by geophysical logging techniques and by X-ray radiography. 

The number of samples required to characterize adequately a coal bed depends on the thickness, quality variability, and size of the deposit. In general, the locations for 

sampling in mines should be separated by distances that are 

comparable to spacings of other outcrop or core locations in 

the same bed. Additionally, two to three closely spaced 

locations (10 to 100m) may yield useful data on local variability of certain quality parameters. 

PURPOSES OF SAMPLING A COAL BED 

Samples submitted for chemical and physical analyses are collected for a variety of reasons, but the 

collection of each sample should always conform to 

certain guidelines. The application of precise techniques 

in sample collection helps to ensure that data from each 

analysis performed on the samples will be useful. For 

interpretations and comparisons of elemental compositions of coal beds to be valid, the samples must be 

collected so that they are comparably representative of 

the coal bed. Such interpretations and comparisons 

should never be based on data from different types of 

samples. 

The purpose in sample collection and the kinds of 

analyses to be performed on the sample dictate the type 

and nature of the sample that should be collected (see 

table 3). For samples used in determining rank, mineralrich layers greater than 1 em must be excluded so that 

only the coal intervals are sampled (ASTM, 1986a). In 

contrast, samples intended for chemical analysis commonly include mineral-rich layers that are less than 10 

em thick (Swanson and Huffman, 1976); samples 

obtained for petrographic analysis generally consist of 

lithologically distinct parts of the coal bed taken at 

separate intervals; and samples intended for washability 

testing may consist of all material, rock and coal, 

between the roof and the floor of the coal bed. 

Table 3. Types of samples and purposes for which samples 

are commonly collected 

>- :::£ Iz :::J 

<( <( 

~ ::l 

>- r.f) r.f) a >- CCI ~ L.U >- ...J Iz :::£ 0 0 I- <( :::J 

0 z ::l ::l :::J I- <( 

<( I- I- <( z ::l i= ~ r.f) r.f) ::l L.U a <( 

u I- ~ L.U a ~ I- z lJ u L.U z u u::: L.U 0 ~ 

> 0 ::l Vi ~ ::l 

<( ...J 0 ~ ~ r.f) 0 0 L.U <( > 0 Q.. r.f) r.f) 

...J Q.. L.U L.U L.U z ~ u <( lJ ~ ~ L.U Q.. 

...J 

L.U COAL ONLY X X ? z WHOLE BED X X X X z 

<( BENCH X X X ? I 

u FACIES X X X X 

COAL ONLY X X ? L.U 

~ WHOLE BED X X X X 

0 BENCH X X X ? u 

FACIES X X X X ? 

COAL ONLY = Sample taken using exclusionary rule 

WHOLE BED = All material between roof and floor of bed 

BENCH = All mineral layers and coal between mineral layers 

FACIES = Laterally extensive subunits of coal bed 

? = Possible sampling for product quality 

lJ 

z 

i= 

r.f) 

L.U 

I-

>- I-

:::J 

CCI 

<( 

I 

r.f) 

<( 

$ 

X 

X 

X 

X 

X 

X 

Sampling of Coal Beds for Analysis 7 
Other purposes may also be best served by channel 

or core samples. If the objective is to represent the 

resources of a coal bed for mine planning and future 

extraction methods, channel and core samples are necessary. In resource and reserve characterization, coal 

sample subtypes include those that represent the whole 

bed, coal facies (laterally extensive parts of the bed), and 

total coal interval. Stratigraphic descriptions of the coal 

bed at and between sample localities should enable 

correlations of subunits, or facies, of the coal bed (fig. 

2). This procedure will aid in understanding abrupt 

quality or thickness changes in the bed. In contrast, if 

the purpose in sample collection is to represent a mined 

product, a properly obtained conveyor-belt sample 

(ASTM, 1986c) may be preferable to channel or core 

samples. 

In some cases, obtaining channel samples may not 

be possible, thus leaving core samples as the only 

practical alternative. Some supplementary coal-quality 

data can be obtained by down-hole geophysical techniques (Lavers and Smits, 1976), regardless of whether a 

core is recovered. 

HISTORICAL PERSPECTIVE OF SAMPLING 

The methods of sampling described by Burrows 

(1907) and Holmes (1911) involve an exclusionary procedure in which the sampler eliminates partings or 

impurities (mineral-rich layers) greater than 1 em and 

lenses or concretions of sulfur or other impurities 

greater than 5 em in diameter and 1.3 em thick "if in the 

judgement of the sampler, they are being excluded by 

the miner from the coal as loaded out of the mine or as 

shipped" (Holmes, 1911, p. 1). The reason for such a 

procedure is "to obtain samples that represent, as nearly 

as possible, the coal that is produced commercially from 

the mine" (Holmes, 1911, p. 8). This was the purpose of 

sampling coal during the early 1900's by the U.S. Bureau 

of Mines and the U.S. Geological Survey (Burrows, 

1907; Campbell, 1907). For the fuel inspectors of the 

U.S. Bureau of Mines, the sampling purpose was qualified to represent the particular mining practice at an 

individual mine and at a specific time. In contrast, the 

samplers from the U.S. Geological Survey attempted to 

approximate the average composition of produced coal 

without regard to site-specific mining practices; therefore, their samplers strictly followed the exclusionary 

procedure. In both methods, partings and pyrite of 

certain thicknesses were excluded from the sample. The 

U.S. Bureau of Mines inspectors excluded only those 

partings excluded by the miner, and the U.S. Geological 

Survey samplers excluded layered, mineral-rich material 

of certain thicknesses. 

8 Methods for Sampling and Inorganic Analysis of Coal 

em in 25110 

0 0 

UNDERCLAY 

Figure 2. Correlation of facies of a single coal bed. 

SAMPLING FOR RANK CLASSIFICATION 

To classify coal by rank, the American Society for 

Testing and Materials (ASTM) refers to the publication 

by Holmes (1911) as the method of sampling (ASTM, 

1986a). In addition, the procedure described by Schopf 

(1960), which restates the rule for exclusion of material, 

attempts to discriminate obvious partings from impure 

coal; the latter is sampled as part of the coal bed. For 

purposes of rank classification, perhaps either variation 

of the procedure is adequate. However, objective criteria 

to distinguish precisely coal from noncoallayers are not 

available. In the calculation of rank-determining values, 

the fixed carbon or calorific-value mineral matter is 

"removed mathematically." This continued practice of 

excluding mineral layers in samples from a bed, even by 

a mathematical correction for mineral matter, is probably an outgrowth of concerns by such early workers as 

Fieldner and Selvig (1930), who proposed that coal rank 

be calculated on a pure-coal or unit-coal basis. 

If an approximation of the characteristics of the 

mined product is needed, perhaps a better sample for 

determining rank would be some mechanical separation 

of a whole-bed sample. The original purpose of the 

exclusion of partings was to approximate or verify more 

closely ash and sulfur concentrations for coal delivered 

by train cars from mined areas (Burrows, 1907; Campbell, 1907). During the days of blasting and hand 

loading of coal, discrimination among impurities could 

be made by those handling the coal. However, highproduction equipment, such as a continuous miner or 

long-wall mining equipment, does not differentiate 

between the coal and the partings during extraction. 

Parting material generally is removed by jigs or air 

tables in the first stage of coal preparation. 
SAMPLING FOR CHEMICAL ANALYSIS 

Another purpose for collecting a channel or core 

sample is to evaluate the chemical composition of the 

coal. Known concentrations and distributions of major, 

minor, and trace elements in a coal bed enable an 

assessment of the possible environmental impacts and 

technological problems that could occur from use of the 

coal. A modification of the exclusionary procedure is 

commonly used because rock partings may contribute to 

the variability in concentrations of certain elements or 

to quality parameters. Shale, siltstone, or nonbanded, 

impure-coal (bone) layers less than 10 em thick are 

included in whole-bed channel samples if it is probable 

that these materials will be mined along with the coal 

(Swanson and Huffman, 1976). Swanson and Huffman 

(1976) also recommended that special samples of noncoal materials be collected to determine their contribution to abnormal elemental concentrations. However, 

"judgement ... must be applied toward obtaining samples which will be most representative of the coal bed" 

(Swanson and Huffman, 1976, p. 2). 

SAMPLING FOR OTHER PURPOSES 

Other purposes of sampling, such as determining 

the coal and the noncoal facies and predicting the 

geometry and quality of a coal bed, may require detailed 

sampling procedures by bench or by coal facies. In these 

procedures, the effects of including or excluding parting 

materials must be assessed. The combined effects of the 

laterally extensive layers of the bed on the quality of the 

whole bed also can be evaluated. 

In all attempts to sample coal beds, the purpose of 

collecting a coal sample determines the criteria applied 

to sampling. Precautions must be taken when comparing certain elemental concentration values so that samples taken for different purposes are not directly compared. For example, in samples collected and analyzed 

to estimate rank, mineral layers greater than 1 em thick 

are excluded, and for samples collected and analyzed to 

determine the trace-element composition, mineral layers 

less than 10 em thick are excluded. Direct comparisons 

of data from these two suites of samples are suspect. 

Thus, ash or sulfur isopleth maps generated from this 

mixed-sample-type set should not be interpreted as being 

related to coal-forming processes. Furthermore, the 

application of the exclusionary procedure does not 

reflect present mining practices. Other questionable 

comparisons may be made if data from bench or facies 

samples are mixed with data from whole-bed samples. 

PROCEDURE FOR CHANNEL SAMPLING 

For both surface and deep mines, the ASTM 

(1986a) standard for collecting channel samples of coal 

should be followed. The following procedures are used 

to collect channel samples of coal. 

1. Select a freshly exposed face to sample. Avoid coal 

ribs or faces that have been "rock dusted" or show 

obvious signs of oxidation, such as red-brown 

stains or efflorescence. In a deep mine, sampling 

of a new face may be possible just after the roof 

has been bolted and before the next cut is made. In 

a surface mine, a fresh face can be sampled 

following the loading stage of mining. 

2. Select a face having a plane that is normal to bedding. 

Coal may be cut back with a hand pick at the top 

and bottom to produce a proper surface. 

3. Spread a 3- x 4-m nylon-reinforced vinyl tarpaulin 

on the floor. 

4. Mark two parallel, vertical lines (using crayon) about 

10 em apart on the coal face, and select the units 

to be included in the sample. If the exclusionary 

procedure is to be followed, the excluded layers 

should be clearly marked. 

5. Using a pick, begin at the bottom of the coal bed and 

chip out the coal between the lines to a depth of 

approximately 8 em; repeat this step from the 

bottom to the top of the channel. 

6. Carefully square the back of the channel so that the 

channel cut is of uniform volume. In surface 

mines, gas-powered masonry cut-off saws may be 

used to cut small channels on either side of the 

10-cm-wide block to be sampled. In deep mines, 

an analogous procedure involves drilling a series 

of holes by hand auger, from top to bottom, on 

both sides of the 10-cm wide block to expose a 

column for sampling. 

7. Transfer the entire sample into polyethylene-lined 

canvas bags or drums. Representative splitting can 

be done later in the laboratory. In the past, 

samples were split in the mine to prevent loss of 

moisture from the freshly removed material. 

Schopf (1960) suggests that a separate sample, 

solely for moisture determination, be taken from 

part of the coal bed and sealed in an air-tight 

container. 

8. Place a properly marked sample tag inside the innermost bag, label the outside container, and seal 

each container separately. 

9. Record a description of the channel, with particular 

emphasis on the thickness of the coal bed subunits. 

PROCEDURE FOR SAMPLING DRILL CORE 

The drill core should be the most representative 

type of sample of a coal bed. However, in some cases, 

coal is lost during coring, and the complete bed is not 

represented by the recovered drill core. In any case, 

geophysical techniques, such as gamma and gammagamma (density) logs, should be used to compare the 

Sampling of Coal Beds for Analysis 9 
NATURAL GAMMA 

em in 

25 ro 

0 0 

HIGH-RESOLUTION 

DENSITY 

\ 

COAL/PARTING 

~PURE 

Figure 3. Natural gamma and high-resolution density 

logs of a coal bed showing log responses of coal and 

impure coal or parting. 

thickness of the bed to the thickness of the core recovered (fig. 3). 

After the drill core barrel is brought to the surface, 

the collection of a core should involve the following 

procedure: 

1. For the split barrel, remove half of the barrel from the 

core. Position split polyvinylchloride (PVC) pipe 

over the exposed core. Remove the barrel after the 

core, barrel, and pipe are rolled over together. For 

the solid barrel, place the PVC pipe at one end of 

the barrel; extrude the core onto the PVC pipe. 

2. Arrange the core with no gaps between pieces. Then, 

measure and describe the core. 

3. Place the second half of the PVC pipe over the core, 

cap and tape the ends of the pipe, and clearly label 

the pipe. 

4. Pull a polyethylene sleeve over the pipe, and seal the 

ends to prevent moisture loss. A moist sponge can 

be placed in the sleeve to prevent further moisture 

loss. 

Next, X-ray radiography (Standards Association of 

Australia, 1982; Stanton and others, 1983) should 

be performed on the core. If the exclusionary 

procedure is used, radiography is a reliable technique for discerning coal from noncoallayers. The 

use of PVC pipe (fig. 4) to encase the coal core 

provides a way to transport the core without 

major disorientation and, in many cases, without 

further breakage. 

10 Methods for Sampling and Inorganic Analysis of Coal 

COAL BED DESCRIPTIONS 

Channel-sampled coal faces should be described 

as completely as possible. Minimally, the thickness of 

the bed, the thickness and stratigraphic positions of 

partings, the pyrite layers, and the mineral-cleat fillings 

should be measured and described. Subunits, or facies, 

that are lithologically distinct and that have lateral 

continuity can be identified by the frequency and thickness of vitrain bands and attritus (Schopf, 1960). Individual layers, such as vitrain (bright, homogeneous 

layers greater than 1 mm thick) and fusain ("charcoal"), 

generally are not laterally continuous; they are commonly lenticular because they form from compressed 

plant stems, leaves, and roots. For the most part, facies 

are composed of assemblages of vitrain and attrital 

layers or other rock that can be identified and recognized in the coal bed (fig. 5). These facies frequently can 

be mapped for miles, and commonly have a narrow 

range of coal quality (fig. 6). 

Visual descriptions of core are difficult to make 

unless the core is broken. Visual descriptions can be 

complemented with data from common down-hole, 

geophysical measurement techniques, such as gamma, 

gamma-gamma (density), and resistivity (Lavers and 

Smits, 1976). A high-resolution geophysical density log 

can provide data that aid in the identification of coal 

facies (fig. 3). High-resolution density logging also can 

provide measurements of thickness to the nearest 3 em 

and a profile of the quality of the coal bed (fig. 3). X-ray 

radiography (fig. 7), combined with visual observation 

of the core and density log, provides another tool for 

recognizing the dominant facies in a core. Comparison 

of an X-ray radiograph to a density log can be used to 

(1) discriminate between layers of pyrite and clay, 

impure coal, and coal, (2) determine which parts of the 

PLASTIC END 

CAPS 

ctJ 

Figure 4. Container for collection of core samples. 
coal bed were not recovered in the core, and (3) identify 

the different facies of the coal bed. 

IDENTIFICATION OF CARBONACEOUS SHALE 

LAYERS 

High-ash coal or mineral-rich partings generally 

are visually distinct in a coal bed. However, in most 

cases, criteria or tests cannot be applied objectively in 

the field to differentiate impure coal (25 to 50 weight 

percent ash) from carbonaceous shale (>50 weight percent ash). Any classification that involves such terms as 

"bone," "billy coal," or "rash" generally has only local 

significance and is not useful for coals of different rank 

or type (Schopf, 1960). Some field methods may provide 

aid in discriminating carbonaceous shale from coal. In 

surface mines, a gamma-ray scintillometer (a hand-held 

instrument) is used to locate impure layers in low-ash 

coal. For the drill core, an X-ray radiograph and a 

gamma-gamma (density) down-hole geophysical log can 

be compared with the coal core. 

FACIES A- Hard, blocky, nonbanded, impure 

coal; shaley, sometimes displaying 

fissility; calcite along cleats. 

FACIES B- Hard, blocky, banded coal with bright 

bands 2 to 3 mm thick alternating with 

attrital (dull) bands 3 to 20 mm thick; fusain 

abundant at top of facies; scattered 

pyrite lenses in basal portion. 

FACIES A'-Hard, blocky, non banded, impure coal; 

conchoidal fracture; moderately bright, 

resinous luster; granular texture; facies 

absent in some places. 

PARTING (ROOF) 

FACIES- Very dark, gray claystone and shale; 

basal portions commonly dark gray 

grading upward into medium gray. 

FACIES C- Bright, banded coal, columnar fracture; 

bright bands 3 to 4 mm thick altemating 

with attrital bands 5 mm thick; distinct 

fusain layers associated with pyrite; 

fusain chips at top; calcite and pyrite 

commonly fill cleats. 

FACIES D- Hard, banded coal broken in large 

blocks; dull luster; bright bands 3 to 

15 mm thick; some cleat calcite, very 

little pyrite; some fusain layers and chips. 

LOWER 

PARTING- Dark gray shale to claystone, 

some places absent. 

FACIES E-Very hard, blocky, banded coal; very 

dull luster; numerous shale layers; 

abundant pyrite in lenses and cleats; 

some calcite in cleats; bright bands 

3 to 4 mm thick; dull bands 2 to 3 em 

thick; slickensides parallel stratification 

in shale layers near base. 

Figure 5. Example of description of generalized stratigraphic section of the Upper Freeport coal bed. 

0 

FACIES 8 

f----e------1 

FACIES C 

~ 

FACIES D 

~ 

FACIES E 

• 

20 

FACIES A ~ 

FACIES A' 

~ 

LOWER PARTING 

40 

ASH YIELD (WEIGHT-PERCENT) 

60 

Figure 6. Ash yields of 134 facies samples of the 

Upper Freeport coal bed. 

For sample collection from deep mines, no comparable instrument that is "mine safe" is available. This 

deficiency in instrumentation creates difficulty when 

applying the exclusionary procedure. However, even if 

this procedure is not followed, another difficulty exists in 

precisely sampling a coal bed at the points of contact 

with adjacent rock strata. Commonly, coal bed contacts 

between the floor and roof rocks are sharp. However, in 

places, contacts are interbedded, transitional, or located 

in a nonbanded layer, particularly at the top of the bed. 

SAMPLING THICK COAL BEDS 

A common practice of sampling thick coal beds 

(greater than 10m thick), either by core or by channel, 

is to divide the bed into intervals no thicker than 1.5 m. 

In many cases, thick coals are sampled in 0. 7 m sections; 

such sampling provides a detailed stratigraphic section 

of the bed. Core samples are best for thick-bed sampling. Beds greater than approximately 3 m thick are 

difficult to sample reliably by the channel method, and 

in many places the thick beds are mined in layers in 

surface mines, thus decreasing the probability of obtaining a fresh sample of the entire bed. Where a high 

resolution density log is obtained, the core can be 

subdivided into lithologically distinct units. 

SUMMARY 

Proper collection of coal samples requires representative material from a coal bed. Uniform volumes by 

core samples, by channel samples, or by properly collected stream (run-of-mine) samples (ASTM, 1986b) are 

the common types. The selection of sample types is 

determined by the purposes of the sampling project or 

program. Certain sample types may not be appropriate 

for particular analyses or comparisons. 

Sampling of Coal Beds for Analysis 11 
0 

I 

TOP 

CM 

5 

I 

BOTTOM 

Figure 7. X-ray radiograph of an undisturbed coal core showing mineral impurities and coal lithotype layers. 

12 Methods for Sampling and Inorganic Analysis ofCoal 
Valid comparisons of analytical data are the user's 

responsibility and depend largely on (1) the types of 

samples, (2) the nature of the samples, such as whole bed 

or bench, and (3) whether mineral layers or coal partings 

are excluded from the sample or are sampled separately. 

REFERENCES 

American Society for Testing and Materials (ASTM), 1986a, 

Standard practice for collection of channel samples of 

coal in the mine (D4596), in 1986 annual book of ASTM 

standards, pt. 5.05, p. 519-521. 

-- 1986b, Classification of coals by rank (D388), in 1986 

annual book of ASTM standards, pt. 5.05, p. 247-252. 

-- 1986c, Standard methods for collection of a gross 

sample of coal (D2234), in 1986 annual book of ASTM 

standards, pt. 5 .05. p. 336-352. 

Burrows, J.S., 1907, The importance of uniform and systematic coal-mine sampling: U.S. Geological Survey Bulletin 

316, p. 486-517. 

Campbell, M.R., 1907, The value of coal-mine sampling: 

Economic Geology, v. 2, no. 1, p. 48-57. 

Fieldner, A. C., and Selvig, W.A., 1930, Present status of ash 

corrections in coal analysis: Classification of coal, American Institute of Mining and Metallurgical Engineers 

(A.I.M.M.E.), p. 51-65. 

Holmes, J .A., 1911, The sampling of coal in the mine: U.S. 

Bureau of Mines Technical Paper 1, 22 p. 

Lavers, B.A., and Smits, L.J.M., 1976, Recent developments 

in coal petrophysics: Transactions of Annual Logging 

Symposium of the Society of Professional Well Log 

Analysis, 17th, Denver, June 9-12, 1976. 

Schopf, J .M., 1960, Field description and sampling of coal 

beds: U.S. Geological Survey Bulletin 1111-B, 67 p. 

Standards Association of Australia, 1982, Guide to the evaluation of hard coal deposits using borehole techniques: 

Australian Standard 2519-1982, North Sydney, Standards Association of Australia, 58 p. 

Stanton, R.W., Moore, T.A., Ruppert, L.F., and Cecil, C.B., 

1983, X-ray radiographic description of coal core as an 

aid for estimating coal quality: Geological Society of 

America Annual Meeting Abstracts, v. 15, no. 6, p. 695. 

Swanson, V.E., and Huffman, Claude, Jr., 1976, Guidelines 

for sample collecting and analytical methods used in the 

U.S. Geological Survey for determining chemical composition of coal: U.S. Geological Survey Circular 735, 11 p. 

Sampling of Coal Beds for Analysis 13 

PREPARATION OF COAL FOR ANALYSIS 

By F.G. Walthall and S.L. Fleming, II 

Abstract 

Bulk quantities of coal weighing 3 to 15 kg are individually reduced to approximately 150 p,m (1 00 mesh) by comminution procedures that minimize contamination by grinding surfaces or by other samples. Seventy grams of each 

pulverized coal sample is oxidized at 525 °C for 36 h to 

determine the percent ash and to provide ash required for 

chemical and instrumental analyses. 

INTRODUCTION 

All procedures described in subsequent sections of 

this bulletin on the chemical and instrumental analysis 

of coals depend upon the comminution step. The pulverization of bulk coal samples from the field serves 

both to homogenize the coal, which typically is quite 

heterogeneous, and to reduce the material to small 

particles needed for rapid ashing and dissolution. The 

comminution of a field sample and the splitting of the 

resulting pulverized sample into portions to be distributed to various laboratories, while minimizing contamination from grinding surfaces, sieves, and other coals, 

are essential to the success of all subsequent chemical 

measurements. Thus, the comminution process is of 

critical importance, and all aspects of the laboratory 

arrangement and of procedures for grinding coals must 

be carefully planned (Swaine, 1985). 

Coals submitted for chemical analysis are first 

received and prepared by the sample preparation (grinding) laboratory. The typical sizes of individual field 

samples vary from 3 to 15 kg. The normal preparation 

procedure requires that each air-dried coal sample pass 

through a jaw crusher; one subsample (split) of the 

crushed material (2 to 4 mm, or 5 to 10 mesh) is then 

taken for the ultimate and proximate analyses, and 

another split is reduced to approximately 150 p,m (100 

mesh) by a vertical grinder for chemical analysis. An 

additional split is kept for archival storage, and the 

excess sample is returned to the submitter. 

EQUIPMENT AND PROCEDURES 

Sample Preparation (Grinding) LaboratoryEquipment 

The instrumentation, equipment, and related items 

required for the safe operation and maintenance of a 

grinding laboratory for coal are listed here. The kiln and 

balance are included because this laboratory both determines the ash from coal and supplies coal ash to other 

laboratories for chemical analysis. 

1. Jaw crusher, partially corrugated manganese steel 

jaw plates, model2X6, Sturtevant Mill Company, 

Boston, MA. 

2. Vertical grinder, alumina ceramic plates with aluminum ring, aluminum ore pan, model 6R (catalog 

no. 242-72A), Bico Braun, Inc., Burbank, CA. 

3. Rolls crusher, 8X5, Sturtevant Mill Company, Boston, MA. 

4. Mixer-mill, model 8000, Spex Industries, Edison, 

NJ. 

. 5. Kiln, 6 kW. 

6. Laboratory balance, 0.005 to 500 g. 

7. Riffle splitter, with pans, Wards Natural Science 

Establishment, Inc., Rochester, NY. 

8. Plastic bag sealmaster, Packaging Aids Corporation, San Francisco, CA. 

9. Sieves, nylon screen in methacrylate rings, 100 mesh, 

Spex Industries, Edison, NJ. 

10. Exhaust hoods, size and location shown in figure 8. 

11. Aluminum pans (23 em circular "pie" pans). 

12. Plastic drying pans, sides less than 38 mm high, 

sample spread less than 25 mm deep. 

13. Porcelain crucibles, 65 to 70 g. 

14. Wire brush, stainless steel. 

15. Spatula, stainless steel. 

16. Polystyrene jars, 120 mL, 5.8-cm diameter, with 

lids. 

17. Polystyrene vials (26 mL) with caps. 

18. Polyethylene vials (polyvials, 3.7 mL) with snap 

caps. 

19. Paper cartons, 0.55 L, 8.5-cm diameter. 

Preparation of Coal for Analysis 15 
20. Plastic bags, 15 x 30 em, sealed by plastic bag 

sealmaster (item 8). 

21. Wax paper, 30 x 46 em. 

22. Lint-free paper towels. 

23. Cleaning sand (clean quartz sand). 

24. Compressed-air supply, filtered, with hose and nozzle. (For safety, the pressure at which the compressed air is supplied should be kept below 0.2 

kPa (30 psi).) 

Safety Equipment and Provisions 

1. Safety goggles for protection of eyes from small 

projectiles and dust from grinding machines, 

Macalaster Bicknell Company, Millville, NJ. 

2. Ear covers (muff type) or inserts for protection from 

loud noises emitted by grinding machinery. 

3. Laboratory coats or coveralls. 

4. Plastic gloves, disposable. 

5. Safety shoes with protective steel toes. 

6. Fire extinguishers (ABC tri-class dry chemical, 5.25 

kg). 

7. Explosion-proof switches and light fixtures in grinding laboratory. 

8. Respirator masks with interchangeable paper filters. 

Safety Procedures 

As in all procedures for the comminution of 

geologic materials, precautions must be taken to protect 

the operator of grinding equipment from dust inhalation, the noise of the machinery, small projectiles emanating from the grinding process for a sample, and 

injury (especially to the hands) that can be inflicted by 

the powerful machinery required for grinding of samples. Moreover, high concentrations of coal dust in air 

can constitute an explosion hazard. Thus, an adequate 

ventilation system and the complete absence of hightemperature sources (cigarettes, sparks from electrical 

switches, electrostatic sparks, flames, etc.) are essential 

for a safe grinding facility for coal. 

Safety goggles, ear protection, a laboratory coat, 

and an air-filter mask should be used at all times while 

operating the crushing and grinding equipment. A rapid 

stream of compressed air, used in cleaning grinder 

surfaces, should always be directed away from the 

operator. Electrical power to grinding equipment should 

be switched off before hands or tools are inserted into 

the machinery. Periodic medical examinations, which 

may include chest X-ray examinations to reveal developing respiratory disorders such as silicosis, are generally considered to be a good preventive measure. 

16 Methods for Sampling and Inorganic Analysis of Coal 

Maintenance of Equipment 

Adequate maintenance of equipment basically consists of regular lubrication and replacement of worn 

components. The following procedure is suggested for 

the grinding laboratory. 

1. Identify all grease fittings and keep the fittings 

capped. 

2. Lubricate each piece of equipment in accordance with 

an established schedule that is posted near the 

device. 

3. Replace worn parts on jaw crusher. 

4. Resurface worn ceramic plates that are used on the 

vertical grinder. 

5. Replace worn drive belts. 

6. Keep drawings and brochures related to equipment 

on file for lists of proper replacement parts and for 

instructions on proper lubrication. 

Sample Preparation (Grinding) LaboratoryFacilities 

The grinding laboratory, which contains heavy 

machinery that is capable of producing significant floor 

vibrations, should be located on the ground floor of a 

building. The laboratory should have no overhead water 

plumbing, including fire-sprinkler systems, because the 

failure, or breakup, of such plumbing presents a serious 

hazard to both the equipment and the operator. Fire 

extinguishers that use carbon dioxide or halon TM are 

suggested. 

The arrangement of the laboratory currently used 

by the U.S. Geological Survey for all grinding procedures on coal is shown in figure 8. This laboratory 

occupies an area of 51 m2 and has four specially 

constructed exhaust hoods that are ducted to a "rotacone" dust collector. Electrical power for equipment is 

made available through eight duplex outlets (single 

phase, 110-V alternating current, 20 A) and four outlets 

providing three-phase, 220-V alternating current, 30 A. 

Compressed air is provided at five outlets, and hot and 

cold tapwater are available at the sink. A water drain is 

located in the center of the floor. 

Adjacent to the laboratory is an office area (31 

m2), in which field sa~·ples are received and information 

concerning each sample is recorded. A sample-drying 

room (20m2

) is used both for short-term storage and for 

drying of samples. Archives of samples are stored in a 

separate area of the facility. 

Crushing and Grinding 

The coal sample, as received from the field, consists of 3 to 15 kg of material that first is reduced to a 

particle size of 2 to 4 mm (5 to 10 mesh) in a jaw crusher. 

This crushed material is then divided into three splits. 
Vertical Vertical Exhaust Cone Grinder Grinder Hood Crusher #1 #2 

Exhaust 

Hood Rolls I Bag Sealer I Crusher 

Floor 

Drain Hammer 

Mill 

I Shatterbox I Jaw Jaw Cabinet Crusher Crusher fY1 Sink 

Warming Desk Coal Floor Oven Cabinet Sink 

Coal Coal 

Vial Cabinet Cabinet 

Shakers 

Balance 

Log-in 

Counter 

Exhaust Kiln Desk fY1 Hood 

Figure 8. Sample preparation laboratories. 

The first split is forwarded to a laboratory for standard 

ultimate and proximate analyses. The second split, 

which is intended for chemical analysis and archiving 

within the U.S. Geological Survey, is pulverized to 150 

Jlm (100 mesh) in a vertical grinder. The remaining split 

is returned to the submitter. These and subsequent steps 

are outlined in figure 9, which is a flowchart that shows 

the treatment and routing of each sample. 

Description of Procedure 

1. Generally, samples are received in plastic bags that 

are tightly packed into a cubic box that has a 

30-cm edge. The individual plastic bags, which 

have been labeled in the field, are removed from 

the box and necessary recordkeeping is first completed. Special grinding and routing instructions 

that accompany the sample are noted on a form 

that also has descriptive information pertaining to 

the coal. 

2. Samples that need air drying are identified. Typically, 

moisture is readily apparent on these samples, or 

the coal powder commonly present in the samples 

does not move about freely as the container is 

agitated. Each of these samples is poured into a 

plastic or aluminum pan, and each of the sample 

numbers is written on a strip of masking tape 

attached to the pan. The empty plastic bag is 

placed under the pan for later use. Wet samples 

typically are air dried for one week; however, 

longer drying times may be required for samples 

that tend to stick to surfaces during grinding. 

3. Containers needed for sample splits from the crushing process are cleaned with a stream of air and 

labeled prior to the crushing procedure. 

4. Samples are taken into the grinding laboratory to be 

crushed one at a time, while the remainder of the 

samples are stored on a cart outside the door of 

the grinding laboratory. This practice reduces the 

possibility of cross contamination. 

5. Just prior to crushing the first sample, the gap 

between the jaws of the jaw crusher is adjusted to 

approximately 4 mm. 

6. After crushing the entire sample, the sample is homogenized by rolling it on a sheet of waxed paper. 

Then, the homogeneous, crushed sample is fed 

into a riffie splitter (fig. 10) to produce splits A and 

B. A minimum of 100 g of sample from the first 

split is poured into the container for samples that 

are intended for ultimate and proximate analyses 

(fig. 10, split A). The second split (fig. 10, split B) 

is fed again into the riffie splitter (fig. 10, splits C 

and D), and a 15-cm-long plastic bag is filled from 

split D for return to the submitter. Split C (fig. 10) 

Figure 9. Sample preparation procedure for coals. 

Preparation of Coal for Analysis 17 
Split crushed sample in riffle 

splitter, filling a pan. 

Placed in a capped 

can, for ultimate and 

proximate analyses. 

(C) 

Q 

l 

Split down into a 

carton, polyvial, and 

a polystyrene vial. 

D. and 

(D) 

Q 

Split into a plastic bag. 

0 All excess sample is returned to the submitter. 

Figure 10. Splitting procedure. 

is distributed into a paper carton (550 mL), a 

polystyrene vial (26 mL), and a snap-cap polyvial 

(3. 7 mL); the paper carton and the polystyrene 

vial are filled approximately two-thirds full, and 

the polyvial is filled to within 3 mm of the top. 

These individual portions are to be used for ashing 

and for subsequent chemical and instrumental 

analyses. All remaining sample is placed in the 

original plastic bag, which is then resealed and 

returned to the submitter. 

7. The simultaneous use of two vertical grinders is 

recommended. This arrangement enables a 

machine operator to pulverize one sample while 

the previously pulverized sample is being split and 

the other grinder is being cleaned. Each sample is 

split by a riffle splitter inside a hood (46 x 61 x 

61 em). 

8. Splits must be prepared for five laboratories: a 20-g 

split for analysis by neutron activation is packaged in a paper carton; a separate 3.5-g sample for 

delayed-neutron determinations of uranium and 

thorium is placed in a polyvial; a 140-g split for 

the ultimate and proximate analyses is placed in a 

metal can; 70 g of coal is split for high-temperature 

18 Methods for Sampling and Inorganic Analysis of Coal 

(525 °C) ashing; and the submitter receives a 140-g 

portion in plastic bags. 

A similar method for preparing coal samples is 

described in the ASTM (1984a) book of standards. 

Ashing Procedure 

Pulverized coal samples are ashed in an electrically 

heated kiln that can ash 40 samples simultaneously. The 

steps followed in the ashing process are listed here. 

1. Forty sequentially numbered porcelain crucibles (or 

evaporating dishes) are cleaned and dried prior to 

ashing the coal samples. The weight of each 

crucible, approximately 70 g, is sufficiently constant to make repeated weighings unnecessary for 

each ashing cycle. 

2. Approximately 70 g of sample is weighed into each 

crucible. Appropriate records are maintained for 

the weights of the sample and the crucible and for 

the sample number or name used by the laboratory. 

3. The crucibles are placed in the kiln. The electrical 

power to the kiln is switched on, and the kiln is 

slowly heated to 200 °C. After the kiln is operated 

at 200 oc for 1.5 h, the temperature is increased to 

350 oc and is maintained at that temperature for 

2 h. Finally, the temperature is increased to 525 oc 

and the ashing is completed at that temperature; 

generally, a period of 36 h is required. 

4. After 36 h, the electrical power is switched off and the 

kiln and samples are allowed to cool (1 to 2 h). 

After the crucibles have cooled to room temperature, the "crucible-plus-ash" weight is measured 

for each sample. These data are recorded, and the 

percent ash is calculated. 

( Weight ash ) Percent ash = Weight coal X 100 

5. Forty 118 mL polystyrene jars are labeled, and three 

6-mm-diameter glass beads are placed in each jar. 

6. Ash from each crucible is then transferred into an 

individual polystyrene jar, and the jar is closed. 

Each jar subsequently is placed into a mixer-mill 

and agitated for 30 s. These homogenized samples 

are provided to the chemical laboratories for 

analysis. 

Another method for determining ash in coal and 

coke is described by the ASTM (1984a) book of standards. 

Cleaning of Work Area and Equipment 

1. Make certain .that the vents on the hoods are open; 

switch on electrical power to the exhaust system. 

2. For the jaw crusher, 

a. Remove loose dust on the plates and surrounding 

area with a fast stream of air from the 

compressed-air line. 
b. Remove buildup of sample on the crusher plates 

with a wire brush, and again blow away loose 

material with a fast stream of air from the 

compressed-air line. 

c. Wipe off the plates with a water-dampened sponge, 

and dry the plates with a stream of air from the 

compressed-air line. 

d. Finally, wipe off the plates with a KimwipeTM 

tissue soaked with acetone. 

e. Blow away loose dust from the pan with a stream 

of air; then, clean the pan with a waterdampened sponge. 

3. For the vertical grinder, 

a. Blow away loose dust from the plates and pan with 

a stream of air. 

b. Pass clean sand through the grinder, as you would 

in grinding a coal sample, and repeat step 3.a. 

4. In the work area and hood, 

a. Wipe the inside of the hood and the counter space 

with a water-dampened sponge. 

b. Dry the cleaned surfaces with a stream of air. 

c. Once each week, thoroughly clean the entire floor 

with a broom and dust pan. Vacuum cleaning 

with a cleaner that does not generate sparks is 

quite appropriate. 

REFERENCES 

American Society for Testing and Materials (ASTM), 1984a, 

D2013-72(1978) Standard method of preparing coal samples for analysis: 1984 annual book of ASTM standards, 

Petroleum products, lubricants, and fossil fuels, sect. 5, 

v. 05.05: Gaseous fuels, coal, and coke: Philadelphia, 

ASTM, p. 298-312. 

-- 1984b, D3174-82 Standard test method for ash in the 

analysis sample of coal and coke from coal: 1984 Annual 

Book of ASTM Standards, Petroleum products, lubricants, and fossil fuels, sect. 5, v. 05.05: Gaseous fuels, 

coal, and coke: Philadelphia, ASTM, p. 401-404. 

Swaine, D.J., 1985, Modern methods in bituminous coal 

analysis: trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 323. 

Preparation of Coal for Analysis 19 

AUTOMATED SEMIQUANTITATIVE 

DIRECT-CURRENT ARC SPECTROGRAPHIC 

DETERMINATION OF 64 ELEMENTS IN COAL ASH 

By A.F. Dorrzapf, Jr., C.J. Skeen, and W.B. Crandell 

Abstract 

A semiquantitative, direct-current arc spectrographic 

method is routinely used to determine 64 elements in coal 

ash. The automated method is rapid and economical for 

evaluating both major and trace-element concentrations. The 

method, a listing of the spectral lines used in the analytical 

scheme, and data from analyses of National Bureau of Standards standard reference coal fly ashes are presented. 

INTRODUCTION 

A semiquantitative, direct-current (de) arc spectrographic method is routinely used to determine 64 elements in coal ash. The automated data acquisition and 

analysis system used in conjunction with this approach 

is an outgrowth of a scanning microphotometer concept 

(Helz, 1965; Helz and others, 1969) that ultimately was 

extended to its present form. The system maintains 

long-term consistency of results and provides archival 

storage capability on both photoplates and microfiche. 

The de-arc spectrographic method is applicable in laboratories without the scanning microphotometer system. 

THE METHOD 

This semiquantitative approach achieves analytical ranges and detectability comparable to those of 

visual estimation procedures (Myers and others, 1961). 

Standards are diluted with a synthetic silicate matrix to 

provide six evenly spaced logarithmic divisions (steps) 

per decade of concentration. When available, natural 

rock standards are preferred over synthetic standards 

and are diluted to correspond to the six steps: 1, 1.47, 

2.15, 3.16, 4.64, and 6.81. Because the standards used 

generally do not match the approximate composition of 

the samples analyzed, the expected accuracy is limited to 

±1 step, which corresponds to roughly +50 or -33 

percent. The procedure is semiquantitative because the 

computer algorithm extrapolates concentrations based 

on prestored coefficients calculated from previously 

arced standards. Analytical curves are not established 

from spectra of standards on the same plate as the 

samples. 

EXPOSURE PROCEDURE 

The operating conditions and the spectrograph are 

described in table 4 (Dorrzapf, 1973). Dilution of the 

sample with graphite increases the uniformity of the 

introduction of the sample into the arc. The spectrograph has been modified to include a two-position mask 

near the focal plane (Helz, 1973). In one position, the 

mask allows only the wavelength regions adjacent to the 

cadmium lines at 274.8 and 441.5 nm to be exposed. The 

spectral lines from a cadmium Osram lamp serve as 

fiducial lines for wavelength calibration. In the other 

mask position, the cadmium "windows" are blocked, 

but the remainder of the spectral region from 230 to 470 

nm is exposed. Thus, spectra from the cadmium lamp 

and the de arc are coexposed without moving the 

photoplate. The Helz jet (Helz, 1964) was chosen rather 

than a Stallwood jet (Stallwood, 1954; Shaw and others, 

1958) because the procedure for changing samples was 

simplified if there was no jet dome to be cleaned. An 

argon-oxygen atmosphere minimizes cyanogen-band formation and thus frees the wavelength region from 

approximately 350 to 420 nm for measurments of 

sensitive lines for Cr, Eu, Gd, K, Mo, Pr, Sc, Sr, Th, Tl, 

W, and Yb. 

THE SCANNING MICROPHOTOMETER SYSTEM 

A scanning microphotometer (Helz, 1973) provides the basis for .all spectral measurements. The optical system for the microphotometer follows conventional practices for good resolution, high contrast, and 

low scattered or diffuse light detection. The fixed 

Automated Semiquantitative D.C. Arc Spectrographic Determination of 64 Elements in Coal Ash 21 
Table 4. Instrumentation and operating conditions 

Instrument or 

Function 

Spectrograph 

Dispersion 

Wavelength range 

Excitation 

Arcing of sample 

Arc gap 

Upper electrode 

Lower electrode 

Atmosphere 

Photoplates 

Operating Conditions 

3.4-m Ebert (Jarrell-Ash Mark Ill). Grating has 600 grooves per mm, and is blazed 

for the first-order ultraviolet region. A 

2-mm high central portion of the arc is 

focused on the collimator by a cylindrical 

quartz lens that has a focal length of 45 

em and is located at the slit. The slit is 

0.025 mm wide and 2.0 mm high. The 

two-step neutral density filter used for 

emulsion calibration and a 14 percent 

transmission neutral density filter are 

located near the slit. The height of the 

mask at the collimator is 18 mm. 

0.5 nm/mm reciprocal linear dispersion, 

first order. 

230.0 to 470.0 nm; first order. 

15-A direct-current arc; current is set 

with a set of graphite electrodes in place 

(the anode cup is empty). The opencircuit voltage from the power supply is 

325 volts. 

15 mg of sample, mixed with 30 mg of 

pure graphite powder, is arced for 20 s at 

a current of 5 A, then the current is 

switched (without interruption of the arc) 

to 15 A for a period of 130 s. 

4 mm, maintained constant throughout 

arcing process. 

Cathode: ASTM type C-6, 3.2-mm diameter x 50-mm long graphite rod. 

Anode: Ultra Carbon No. 3170, 6.3-mm 

diameter, thin-walled graphite. 

Mixture of 70 percent argon plus 30 

percent oxygen; flow of 6.6 L/min 

directed by a ceramic jet concentric to the 

anode (Helz, 1964). The top of the jet 

nozzle is positioned 2 mm below the top 

of the anode. 

Eastman-Kodak III-0 emulsion, 102 x 

508 mm glass plate. Exposed emulsion is 

processed in D-19 for 3.25 min, fixed for 

10 min, washed for 30 min, and dried by 

a flow of warm air for 30 min. 

entrance slit consists of a precision ruled window (1 00 

J!m wide) in a mirror. A 32-mm focal length MicroTessarTM lens focuses an image one-tenth the slit size on 

the plane of the spectrum. The optics are designed to 

sample a portion of the spectrum 1 mm high by 7 J!m 

wide (about a quarter of the width of a spectral line). 

The optical system is mounted on a MooreR no. 3 

measuring machine. Lateral motion of the milling 

machine bed, on which the photoplate rests, is accomplished by a precision lead screw. The signal produced 

by light passing through the photographic emulsion and 

detected by a solid-state detector is sampled by an 

22 Methods for Sampling and Inorganic Analysis of Coal 

analog-to-digital (A/D) converter that is gated by a 

rotating shaft encoder attached directly to the ring 

motor that drives the screw. A scanning speed of 70 s per 

spectrum provides a practical interval for data collection 

and minimizes vibrational effects on the optical system 

and thermal and mechanical wear on the screw. The 

photoelectric signal is sampled at 5-J!m increments of 

plate motion that correspond to wavelength changes of 

0.0025 nm. Spectral lines can be located with a reproducibility of ±0.005 nm. During a scan of the spectrum 

from 230.0 to 470.0 nm, approximately 92,000 transmission measurements are made, corresponding to a 

sampling rate of 1.3 kHz. 

THE MINICOMPUTER CONFIGURATION 

The heart of the signal processing system is a 

Hewlett-PackardR 2100S minicomputer that has 32 kilobytes of random-access memory. 

The operator of the microphotometer controls the 

computer via a model 2615A terminal when recording 

plates. The portion of computer memory that remains 

after installation of the real time executive operating 

system (RTE II) is divided into a small foreground (5 

kilobytes) and a large background area (16 kilobytes). 

Programs are run concurrently in both areas. The data 

acquisition program runs in the foreground, while data 

reduction programs are operating in the background. 

The Hewlett-PackardR 91000A AID converter uses a 

differential input when sampling voltages and is gated by 

a square-wave timing pulse from the shaft encoder. A 

specially written assembly language driver, which allows 

a sampling rate up to 40 kHz, controls the operation of 

the AID converter. All 92,000 voltage measurements, 

which constitute a scan, are dumped into a file on the 

Hewlett-PackardR 7900A 5-megabyte disk. Although 

the resolution of the AID converter is 1 part in 10,235, 

only 1 part in 1,000 is needed for this work. 

Within 5 min of recording the last spectrum on a 

photoplate, the necessary number of two-page report 

forms listing the concentrations of 64 elements for as 

many as 10 samples are printed on a model 2607 A line 

printer. Information about effective arc temperature 

and electron pressure during each arcing (Golightly and 

others, 1977) and the calculated total oxides (considering only major constituents) for each sample are printed 

on a separate page. The program next writes an ASCII 

magnetic tape that contains detailed data on plate 

emulsion calibration and on each spectral line. These 

data are processed on an International Business 

MachineR 370 computer to produce a second tape that is 

organized for input to the QuantorR 105 microfiche 

recorder. However, information can also be printed out 

on the line printer to provide the detailed analysis 

immediately. 
DATA HANDLING 

Programs for data collection and interpretation 

have been written by Walthall (1974) to use on a 

mainframe computer and by Thomas (1979) to use on 

the minicomputer system just described. 

WAVELENGTH CALIBRATION 

The two cadmium fiducial lines coexposed on each 

spectrum, through specially masked windows, are used 

for wavelength calibration. The computer program 

searches each of these windows for the first line with a 

transmittance below some predetermined threshold. The 

lines thus located are accepted as the cadmium fiducial 

lines. The number of readings (transmission measurements) between these cadmium lines is compared with 

the expected number of readings; a discrepancy of more 

than ± 1 reading is assumed to correspond to an expansion or contraction of the spectrum due to temperature 

variation or a change in the optics. The first task, then, 

is to calculate the estimated positions of iron and analyte 

lines relative to Fe 233.2 nm, using the dispersion of the 

spectrograph-microphotometer system in units of the 

number of percent transmission readings per nanometer. The expected positions of all the other iron or 

analyte lines are calculated by applying corrections to 

their estimated positions relative to Fe 233.2 nm. 

CONCENTRATION CALIBRATION 

Both single- and multiple-element standards are 

arced to provide the working relationships between 

concentration and spectral line intensity required for the 

analytical curve for each spectral line of each analyte 

element. For each analyte line, a series of programs 

produce a single page of output on which are tabulated 

intensities of the line in all the spectra on the photoplate. 

The tabulation includes the percent transmittances of 

the peak and background of the analyte line and neighboring lines within ±0.0175 nm, the relative intensity of 

the analytical line, and the concentration. The output 

also presents an evaluation of the suitability of the line 

for analyses that is based on the shape and intensity of 

the line and the number of readings away from the 

estimated position at which the line was located in each 

spectrum. 

The computer algorithm calculates the coefficients 

of first- and second-degree polynomials for the analytical curve of the natural logarithm of intensity versus the 

natural logarithm of concentration. It evaluates the 

curve for range, goodness of fit, and slope, and suggests 

a working concentration range for the line, with a lower 

limit defined by a signal-to-noise ratio of 2. 

The analyst evaluates the analytical usefulness of 

each line on the basis of profile, intensity, and location. 

The coefficients of the analytical curve are automatically 

entered into a data base. When the process is complete 

for each analyte line, the data base is defined as the 

wavelength table for the system. For each analyte line in 

wavelength order, the table contains the element symbol, wavelength, line priority, determination limits, and 

coefficients of the second-degree polynomial that are 

used to determine the concentration of the analyte in the 

sample. A list of the spectral lines and determination 

limits for each line are given in table 5. 

SPECTRAL-I NTE RFE RE NCE CORRECTIONS 

On the basis of elemental concentrations determined for standard reference materials, interferences 

can be identified and line priorities and concentration 

ranges adjusted to minimize systematic errors (Thomas, 

1979). 

Generalized interference treatments are of two 

types, subtraction or line switching. The subtraction 

routine makes corrections by subtracting an equivalent 

concentration contributed by the interfering line. This 

subtraction uses predetermined coefficients, relating the 

concentration of interference to apparent concentration 

of analyte. 

The line-switching treatments are of three types. 

Two are used when the analyte line is hidden by an 

interference. One type gives no estimate of concentration. The computer then checks the concentration of the 

interference to be sure that it is high enough to interfere 

and checks the computerized evaluation of the profile of 

the line to be sure that the line is obscured. In the second 

type, if both of the previous conditions are met, the 

computer algorithm switches to an auxiliary line, which 

may give a concentration greater than the upper limit of 

the last interference-free line in the priority scheme. The 

third line-switching treatment is designed to guard 

against spurious answers from band lines, scratches, or 

ghosts. Here, one or two similar, more abundant, 

elements, such as platinum and palladium for the noble 

metals series, are monitored. For this example, if platinum or palladium is not reported, the algorithm switches 

to a less-sensitive line for ruthenium and reports less 

than its lower limit of determination. 

PLATE EMU LSI ON CAll BRA liON 

A modified (Walthall, 1974) Churchill two-step 

procedure is used for emulsion calibration. The recorded 

spectrum is divided into ten 25-nm segments. Twenty-six 

iron lines are used to define the preliminary plate 

emulsion curve in each 25-nm segment. These iron lines 

Automated Semiquantitative D.C. Arc Spectrographic Determination of 64 Elements in Coal Ash 23 
Table 5. Spectral lines used in spectrographic analysis, listed in order of decreasing intensity 

Ele- Wavelength Determination limits Ele- Wavelength Determination limits Ele- Wavelength Determination limits 

ment (nm) (cg/g) ment (nm) (cg/g) ment (nm) (cg/g) 

Ag ... 328.068 0.000010 - 0.00215 Ho ... 345.600 0.000681 - 0.0147 Ru ... 349.894 0.000215 - 0.0100 

338.289 0.000100 - 0.00215 339.898 0.00100 - 0.0316 343.674 0.000464 - 0.0215 

235.792 0.100 - 1.00 328.198 0.00681 - 0.100 408.060 0.000681 - 0.0681 

AI ... 266.039 0.0464 - 1.47 In ... 451.132 0.00100 - 0.0147 291.626 0.00464 - 1.00 

265.249 0.0464 - 3.16 303.936 0.00100 - 0.0464 Sb ... 259.806 0.00681 - 0.215 

237.841 0.316 - 31.6 325.856 0.00147 - 0.147 326.750 0.0100 - 0.681 

266.917 2.15 - 31.6 293.262 0.00316 - 1.00 267.064 0.0681 - 1.00 

As ... 286.045 0.0100 - 1.00 271.027 0.0464 - 1.00 268.276 0.147 - 1.00 

234.984 0.0147 - 1.00 Ir .... 322.778 0.00147 - 0.464 Sc ... 424.683 0.000100 - 0.00316 

289.871 0.464 - 1.00 247.512 0.0147 - 1.00 391.181 0.000100 - 0.00464 

Au ... 267.595 0.000681 - 0.0316 K .... 404.414 0.0681 - 2.15 402.040 0.000147 - 0.00681 

242.795 0.00147 - 0.147 404.720 0.147 - 3.16 335.373 0.000147 - 0.0100 

B .... 249.773 0.000316 - 0.0215 344.637 1.00 - 10.4 255.236 0.00215 - 0.100 

249.679 0.000681 - 0.0464 La ... 404.291 0.00100 - 0.0681 Si ... 251.921 0.00464 - 0.0681 

Ba ... 455.404 0.000147 - 0.00316 433.373 0.00215 - 0.0464 253.238 0.100 - 14.7 

413.066 0.00215 - 0.0681 324.512 0.00215 - 0.215 243.878 0.215 - 21.5 

350.112 0.00464 - 0.681 350.999 0.0215 - 1.00 257.713 2.15 - 34.3 

307.159 0.0215 - 3.16 Li ... 323.261 0.00681 - 0.316 Sm ... 429.675 0.00100 - 0.0100 

Be ... 313.042 0.000100 - 0.00147 427.328 0.215 - 3.16 425.640 0.00316 - 0.100 

313.107 0.000100 - 0.00316 Lu ... 291.139 0.00147 - 0.100 340.867 0.00464 - 0.100 

234.861 0.000100 - 0.00681 451.857 0.0147 - 0.100 Sn ... 317.502 0.000464 - 0.0464 

332.134 0.000215 - 0.0147 Mg ... 277.983 0.00215 - 0.147 283.999 0.00147 - 0.0464 

332.109 0.000215 - 0.0147 278.142 0.00316 - 0.681 286.333 0.00681 - 0.100 

265.062 0.000215 - 0.0215 332.993 0.100 - 4.64 242.169 0.0100 - 1.00 

249.473 0.00100 - 0.0681 293.854 0.147 - 10.0 Sr ... 407.771 0.000100 - 0.000464 

Bi .... 306.772 0.00100 - 0.0215 457.115 4.64 - 30.4 460.733 0.000215 - 0.00681 

289.796 0.00316 - 0.316 Mn ... 279.827 0.000100 - 0.0147 346.446 0.00147 - 0.100 

302.464 0.00464 - 0.681 280.106 0.000147 - 0.0215 416.179 0.0147 - 0.464 

Ca ... 317.933 0.00100 - 0.147 294.921 0.000316 - 0.0464 293.183 0.316 - 14.7 

315.887 0.00464 - 0.316 293.306 0.00100 - 0.147 330.753 0.464 - 21.5 

299.731 0.0681 - 10.0 291.460 0.0215 - 3.16 256.947 1.47 - 31.6 

272.165 0.681 - 31.6 271.333 0.464 - 21.5 Ta ... 271.467 0.0316 - 1.00 

Cd ... 326.106 0.00316 - 0.147 238.702 10.0 - 46.4 296.555 0.0464 - 1.00 

346.620 0.00316 - 0.215 Mo ... 317.035 0.000100 - 0.0316 284.425 0.0464 - 1.00 

325.253 0.100 - 1.00 320.883 0.00100 - 0.100 294.022 0.100 - 1.00 

Ce ... 418.660 0.00430 - 0.136 281.615 0.00215 - 0.100 Tb ... 329.307 0.00316 - 0.100 

416.561 0.00632 - 0.200 Na ... 330.232 0.00215 - 0.464 365.888 0.00464 - 0.100 

320.171 0.0200 - 0.928 330.299 0.00681 - 1.00 427.851 0.0215 - 0.100 

314.528 0.0200 - 2.00 285.303 0.100 - 7.96 Th ... 401.913 0.00464 - 0.215 

Co ... 345.351 0.000100 - 0.00681 285.283 0.147 - 7.96 340.270 0.0100 - 1.00 

341.234 0.000215 - 0.0147 Nb ... 316.340 0.000681 - 0.100 332.513 0.0147 - 0.681 

344.917 0.000215 - 0.0316 319.498 0.000681 - 0.100 411.672 0.0316 - 0.681 

341.263 0.000464 - 0.0464 295.088 0.00100 - 0.100 287.041 0.0147 - 1.00 

339.538 0.00215 - 0.0681 Nd ... 430.357 0.00316 - 0.0681 Ti ... 264.426 0.00316 - 2.15 

335.438 0.00316 - 0.316 435.817 0.00681 - 0.316 264.110 0.0100 - 2.15 

326.082 0.0316 - 1.47 438.566 0.0215 - 0.464 267.993 0.0464 - 10.0 

238.346 0.0316 - 2.15 436.863 0.0464 - 1.00 245.044 1.47 - 46.4 

Cr ... 357.869 0.000100 - 0.00147 Ni ... 305.082 0.000147 - 0.0316 Tl ... 377.572 0.00100 - 0.0215 

302.435 0.000681 - 0.100 342.371 0.000316 - 0.0464 351.924 0.00100 - 0.0464 

301.519 0.00100 - 0.100 310.188 0.000681 - 0.0681 276.787 0.00215 - 0.316 

342.121 0.00316 - 0.681 294.391 0.00464 - 0.316 352.943 0.0147 - 0.316 

Cu ... 324.754 0.000100 - 0.00147 299.260 0.00464 - 0.316 237.969 0.100 - 1.00 

327.396 0.000100 - 0.00464 282.129 0.0316 - 1.00 Tm ... 346.220 0.000464 - 0.0215 

282.437 0.00316 - 0.147 340.953 0.0464 - 1.47 409.418 0.00215 - 0.0464 

301.084 0.0215 - 0.147 Os ... 330.156 0.00147 - 0.464 325.804 0.00215 - 0.100 

Dy ... 345.433 0.00215 - 0.100 326.795 0.00316 - 0.464 339.995 0.00464 - 0.100 

331.989 0.00464 - 0.100 290.906 0.00316 - 0.681 u .... 286.568 0.0215 - 1.00 

Er ... 323.059 0.000464 - 0.0681 P .... 255.493 0.0681 - 6.81 378.284 0.0464 - 1.00 

332.320 0.00147 - 0.100 Pb ... 283.307 0.000681 - 0.0316 424.437 0.100 - 1.00 

322.073 0.0100 - 0.100 368.347 0.000681 - 0.0316 v .... 310.230 0.000100 - 0.0215 

Eu ... 412.973 0.000215 - 0.00681 363.958 0.00147 - 0.0464 318.341 0.000215 - 0.0316 

420.504 0.000316 - 0.00681 261.418 0.00215 - 0.100 311.838 0.000215 - 0.0464 

281.395 0.00147 - 0.100 266.317 0.00681 - 0.100 319.801 0.00147 - 0.100 

290.668 0.00464 - 0.100 Pd ... 324.270 0.000100 - 0.0100 267.932 0.00464 - 0.100 

272.778 0.00464 - 0.100 351.694 0.000464 - 0.0147 w ... 400.875 0.00147 - 0.215 

Fe ... 283.244 0.00743 - 1.60 346.077 0.000681 - 0.0215 289.645 0.00681 - 1.00 

294.134 0.0160 - 3.45 306.531 0.00316 - 0.464 294.698 0.0100 - 1.00 

317.545 0.0743 - 7.43 Pr ... 405.654 0.0100 - 0.100 Y .... 321.668 0.000147 - 0.0147 

236.202 0.345 - 23.5 414.126 0.0147 - 0.100 324.228 0.000147 - 0.0147 

239.147 1.09 - 23.5 403.936 0.0147 - 0.100 332.788 0.000147 - 0.0316 

Ga ... 294.364 0.000147 - 0.0316 Pt ... 306.471 0.000215 - 0.0464 319.562 0.000681 - 0.0681 

294.418 0.00147 - 0.100 299.797 0.000681 - 0.100 434.879 0.0464 - 1.00 

Gd ... 354.937 0.00316 - 0.100 265.945 0.000681 - 0.100 Yb ... 328.937 0.000015 - 0.00215 

302.761 0.00316 - 0.100 283.030 0.00315 - 0.215 398.799 0.000100 - 0.00316 

333.139 0.00464 - 0.100 262.803 0.0215 - 0.464 289.138 0.000681 - 0.0464 

Ge ... 265.118 0.000464 - 0.0316 331.505 0.0316 - 1.00 345.407 0.00316 - 0.100 

303.906 0.000464 - 0.0316 Re ... 346.047 0.00100 - 0.147 Zn ... 334.502 0.00100 - 0.100 

326.949 0.00147 - 0.147 346.472 0.00147 - 0.147 334.557 0.00681 - 0.681 

265.158 0.00316 - 0.147 334.620 0.100 - 1.00 277.087 0.0681 - 1.00 

241.737 0.0147 - 1.00 350.306 0.147 - 1.00 Zr ... 327.305 0.000316 - 0.100 

Hf ... 291.648 0.00147 - 0.464 264.905 0.316 - 1.00 327.927 0.000464 - 0.147 

339.980 0.00316 - 0.464 Rh 339.685 0.000215 - 0.0100 347.939 0.000681 - 0.316 

310.912 0.0147 - 1.00 346.204 0.000464 - 0.0316 348.115 0.00464 - 0.316 

318.905 0.0215 - 1.00 408.122 0.00681 - 0.464 

272.261 0.0100 - 2.15 

270.013 0.0147 - 2.15 

24 Methods for Sampling and Inorganic Analysis of Coal 
and the exposure time for the two-step iron spectrum are 

selected so that the transmittance regions <20 percent, 

20 to 80 percent, and >SO percent are approximately 

equally represented. The preliminary emulsion calibration curve (natural logarithm of percent transmittance 

of filtered step versus the natural logarithm of percent 

transmittance of unfiltered step) is represented by a 

quadratic equation. The 45° tangent to the curve is used 

as a starting place for finding the inflection point of the 

logarithm of relative intensity versus the logarithm of 

percent transmittance of the final plate emulsion curve. 

The actual inflection point is defined as the point from 

which one step of the filter factor on either side produces 

an equal change on the logarithm percent transmittance 

scale. The Newton method of successive approximation 

(Abramowitz, 1964) is used to find this point on the 

preliminary curve. The inflection point is then translocated to the final curve so that it falls on the line with a 

45 o slope that passes through the point where the 

relative intensity equals 106 and the percent transmittance equals 0.1 percent. 

QUALITY CONTROL 

Two other computer programs detect possible 

analysis errors. Each photoplate contains spectra from 

one to three reference materials in addition to spectra 

from up to 23 samples and an iron two-step calibration 

spectrum. The reference materials are selected from 20 

well-characterized standards, such as U.S. Geological 

Survey (USGS) diabase W -2, USGS granite G-2, or 

National Bureau of Standards (NBS) 1633a coal ash, 

chosen to represent the variety of materials commonly 

analyzed. The analyst selects standards that are compositionally similar to the samples on the basis of the 

description of the samples provided by the scientist 

requesting the analyses. The computer program recognizes these standards and compares the concentrations 

determined for Si, Al, Fe, Ca, Mg, Ti, Co, Pb, and Zr 

with accepted analyte concentrations for these standards. These nine elements include the major rock 

constituents, have a wide range of volatility in the de 

arc, and enable checks for loss of refractory elements 

that would occur if a molten bead is lost from the anode 

during the arcing process. If the concentration computed for any of these elements is more than one step 

away from the accepted concentration, a message is 

printed comparing the reported value with the accepted 

value. Another program computes and tabulates total 

oxides, effective temperature, and electron pressure for 

each sample. Total concentration of oxides is computed 

by converting concentrations of the rock-forming elements (Si, AI, Fe, Mg, Ca, Na, K, Ti, P, and Mn) to 

concentrations of the individual oxides and by summing 

the results. Ideally, the total concentration of oxides for 

a silicate rock equals 100 percent. 

In the analyses of coal ash, for evaluation of both 

precision and accuracy of this method, NBS standard 

reference materials 1633 and 1633a (NBS, 1975, 1979) 

are routinely included as control samples in the analytical procedure. Table 6 lists the concentrations provided 

by NBS certificates, the mean concentrations determined 

in U.S. Geological Survey laboratories over an 11-month 

period, and the associated relative standard deviations. 

These data were accumulated during a period that 

coincides with the analyses of over 2,000 coal-ash 

samples. 

CONCLUSIONS 

The automated de arc em1ss1on spectrographic 

analysis of coal ash is a rapid, economical method for 

evaluating both major and trace-element concentrations. Concentrations determined for coal ash are within 

the limits of precision and accuracy for which the 

method was designed. The high relative standard deviations for barium and zirconium indicate the heterogeneity documented for these reference materials (Filby, 

1985). The system has the capability for the analysis of 

4,000 samples, or 256,000 determinations, per year of 

effort by a single analyst. 

REFERENCES 

Abramowitz, Milton, 1964, Elementary analytical methods, in 

Abramowitz, Milton, and Stegun, LA., eds., Handbook 

of mathematical functions: National Bureau of Standards 

applied mathematics series 55, Washington, D.C., U.S. 

Government Printing Office, chap. 3, p. 18. 

Dorrzapf, A.F., Jr., 1973, Spectrochemical computer analysis-argon-oxygen D.C. arc method for silicate rocks: 

U.S. Geological Survey Journal of Research, v. 1, no. 5, 

p. 559-562. 

Filby, R.H., Nguyen, Son, Grimm, C.A., Markowski, G.R., 

Ekambaram, Vanavan, Tanaka, Tsuyoshi, and Grossman, Lawrence, 1985, Evaluation of geochemical standard reference materials for microanalysis: Analytical 

Chemistry, v. 57, no. 2, p. 551-555. 

Golightly, D.W., Dorrzapf, A.F., Jr., and Thomas, C.P., 

1977, Sets of spectral lines for spectrographic thermometry and monometry in D.C. arcs of geologic materials: 

Spectrochimica Acta, v. 32B, p. 313-325. 

Helz, A.W., 1964, A gas jet for D.C. arc spectroscopy: U.S. 

Geological Survey Professional Paper 475-C, p. 

D176-D178. 

__ 1965, The problem of automatic plate reading and 

computer interpretation for spectrochemical analysis: 

U.S. Geological Survey Professional Paper 525-B, p. 

B160. 

__ 1973, Spectrochemical computer analysis instrumentation: U.S. Geological Survey Journal of Research, v. 1, 

no. 4, p. 475-487. 

Helz, A.W., Walthall, F.G., and Berman, Sol, 1969, Computer analysis of photographed optical emission spectra: 

Applied Spectroscopy, v. 23, no. 5, p. 508-518. 

Automated Semiquantitative D.C. Arc Spectrographic .Determination of 64 Elements in Coal Ash 25 
Table 6. D.C. Arc Spectrographic Analyses of NBS Standard Reference Material Coal Fly Ash 

[Concentration units are % (cg/g) for the first group of elements, including Si through Mn, and ppm (~-tg/g) for the group of elements that 

includes As through Zr.] 

1633 1633A 

ELEMENT NBS VALUEa USGS AVERAGEb NBS VALUEa USGS AVERAGEC 

Si (OJo) 27 ± 3.3 22.8 ± 0.8* 26 ± 2.6 

AI 17 ± 2.8 14 18 ± 3.1 

Fe 8.0 ± 0.93 9.40 ± 0.10* 11 ± 1.7 

Mg 2.2 ± 0.32 0.455 ± 0.010* 0.71 ± 0.14 

Ca 5.4 ± 1.2 1.11 ± 0.01 * 1.3 ± 0.31 

Na 0.25 ± 0.03 0.17 ± 0.01 * 0.16 ± 0.03 

K 1.72 1.3 ± 0.15 1.88 ± 0.06* 1.5 ± 0.19 

Ti 0.80 ± 0.15 0.8 0.85 ± 0.18 

Mn 0.0493 ± 0.0007* 0.076 ± 0.011 0.0190 0.026 ± 0.0777 

As(ppm) 61 ± 6* <100ct 

B 

Ba 

Be 

Ce 

Co 

Cr 

Cu 

Eu 

Ga 

La 

Mo 

Nd 

Ni 

Pb 

Sc 

Sr 

v 

y 

Yb 

Zn 

Zr 

430 440 

1600 

12 15 

170 

38 38 

131 ± 2* 120 

128 ± 5* 100 

3.1 

49 39 

96 

-

60 

98 ± 3* 110 

70 ± 4* 74 

25 

1380 1700 

214 ± 8* 200 

53 

6.6 

210 ± 20* 260 

180 

a certified values indicated with *; others not certified 

b average of 35 determinations 2/83 to 7/83 

c average of 31 determinations 6/83 to 3/84 

d lower limit of determination 

± 46 

± 490 

± 1.5 

± 29 

± 4.9 

± 23 

± 25 

± 0.5 

± 5.8 

± 13 

-

± 15 

± 15 

± 9.0 

± 4.0 

± 230 

± 24 

± 7.8 

± 0.9 

± 21 

± 29 

Myers, A.T., Havens, R.G., and Dunton, P.J., 1961, A 

spectrochemical method for the semiquantitative analysis 

of rocks, minerals, and ores: U.S. Geological Survey 

Bulletin 1084-I, p. Il-1229. 

National Bureau of Standards (NBS), 1975, Certificates of 

analysis, standard reference material 1633: Washington, 

D.C., Office of Standard Reference Materials, U.S. 

Department of Commerce. 

-- 1979, Certificate of analysis, standard reference material 1633a: Washington, D.C., Office of Standard Reference Materials, U.S. Department of Commerce. 

Shaw, D.M., Wickremasenghe, 0., and Yip, C., 1958, A 

26 Methods for Sampling and Inorganic Analysis of Coal 

145 ± 15* 190 ± 49 

32 ± 4.0 

1500 910 ± 160 

12 14 ± 1.9 

180 160 ± 53 

46 38 ± 6.2 

196 ± 6* 180 ± 33 

118 ± 3* 93 ± 21 

4 3.4 ± 0.6 

58 54 ± 11 

29 28 ± 6.2 

100 ± 29 

127 ± 4* 140 ± 19 

72.4 ± 0.4* 76 ± 12 

40 29 ± 5.7 

830 ± 30* 900 ± 140 

300 240 ± 36 

220 ± 10 270 ± 41 

simple device for the spectrochemical analysis of minerals 

in an inert atmosphere using the Stallwood jet: Spectrochimica Acta, v. 13, no. 3, p. 197-201. 

Stallwood, B.J., 1954, Air-cooled electrodes for the spectrochemical analysis of powders: Journal of the Optical 

Society of America, v. 44, no. 2, p. 171-176. 

Thomas, C.P., 1979, A minicomputer-based emission spectrographic analysis system dependent on scanning microphotometry: Applied Spectroscopy, v. 33, no. 6, p. 604-612. 

Walthall, F.G., 1974, Spectrochemical computer analysisProgram description: U.S. Geological Survey Journal of 

Research, v. 2, no. 1, p. 61-71. 
THE DETERMINATION OF 41 ELEMENTS IN 

WHOLE COAL BY INSTRUMENTAL NEUTRON 

ACTIVATION ANALYSIS 

By C.A. Palmer and P.A. Baedecker 

Abstract 

Forty-one elements have been determined in coal by a 

combination of short and long irradiations using instrumental 

neutron activation analysis (I NAA). The factors that lead to 

errors in analysis, such as spectral overlaps, low sensitivity, 

and multiple sources of the indicator radionuclide, are discussed. Detection limits for the elements determinable by 

INAA are given and data for National Bureau of Standards coal 

and fly ash standards are presented. 

INTRODUCTION 

Instrumental neutron activation analysis (INAA) 

is a versatile technique for elemental analysis because it 

has very low detection limits for many elements, lends 

itself to automation, and provides precise data for many 

major, minor, and trace elements. The application of 

INAA to the analysis of coal has been described in a 

number of publications (e.g., Block and Dams, 1973; 

Ondov and others, 1975; Rowe and Steinnes, 1977a, b; 

Swaine, 1985). For analyses based on the measurement 

of long-lived nuclides (t Y

2 > 1 day), 30 elements can be 

determined routinely in most coal samples. Two additional elements can be determined in certain coals. 

Extension of the technique to the measurement of 

short-lived activities, with rapid sample transfer and 

short irradiation and counting times, makes possible the 

determination of an additional nine elements. 

ACT IVA liON ANALYSIS 

Activation analysis is based on the measurement 

of the activity from radionuclides that are produced by 

nuclear reactions on naturally occurring isotopes of the 

element to be determined in the sample. Reactor neutrons are most commonly used for inducing the nuclear 

transformations because of their availability, their relatively high probability for neutron-induced reactions, 

and their relative freedom from problems due to matrix 

effects (self-shielding). For example, the determination 

of arsenic is carried out by the following reaction: 

75 As + n - 76 As + 'Y 

76 As t_Y:_2 __ 26_._3_h 76Se + {3 + 'Y 

where the amount of arsenic in the sample is determined 

by counting the induced 76 As activity. The activity of the 

indicator radionuclide produced during the irradiation 

is directly proportional to the amount of element of 

interest in the sample, and the analytical determination 

is generally made by comparing the activity induced in 

the sample against the activity measured for wellcharacterized standard samples. The activities of the 

samples and standards are most commonly measured by 

gamma-ray spectroscopy because potentially interfering 

activities can generally be discriminated against by 

looking at gamma-rays having unique energies for the 

indicator radionuclide and because gamma counting is 

relatively free from matrix effects (self-absorption). 

Semiconductor detectors, such as high-purity germanium and lithium-drifted germanium (Ge(Li)) diodes, 

are generally used for gamma-ray spectroscopy because 

of their excellent resolution, which permits the s~paration of closely spaced lines. These devices convert the 

gamma-ray signal for the irradiated samples to electrical 

signals that can be sorted according to amplitude by an 

analog-to-digital converter; the pulses within each amplitude interval are counted by a multichannel scaler, with 

each channel corresponding to a given interval of gamma 

energy. A typical gamma-ray spectrum of an irradiated 

coal sample, measured 5 days after irradiation, is shown 

in figure 11. The radioactivity in the sample is thus 

measured by determining the area of a specific gamma 

photopeak of interest above an underlying background 

continuum. 

If only relatively long-lived (tY2 > 12 h) indicator 

radionuclides are employed in the analysis, up to 32 

The Determination of 41 Elements in Whole Coal by Instrumental Neutron Activation Analysis 27 
::J' 

w 

z 

z 

<( 

:I: 

0 

a: 

w 

a.. 3.0 

(/) 

1-

z 

::::> 

0 

Q 2.0 

(!) 

0 

....J 

1.0 

Br 

Br Br 

Br Br Br Na 

Br 

Br La 

Na 

K 

CHANNEL NUMBER 

Figure 11. Spectrum of NBS coal standard 1632 collected 5 days after irradiation. 

elements can be determined using relatively long irradiations and two sample counts following irradiation. The 

elements, their indicator radionuclides, half-lives, 

gamma-ray lines, detection limits, and potential spectral 

interferences are listed in table 7. The estimation of 

detection limits for INAA is subject to considerable 

uncertainty. This uncertainty exists because the estimate 

is based on the signal-to-background ratio for each 

photopeak of each sample being counted and the Ge(Li) 

~ detector employed, where the Compton continuum from 

higher-energy gamma-rays contributes to the background. The detection limits are therefore dependent on 

sample composition. These detection limits, presented in 

table 7, are for coal samples having concentrations of 

Na, Sc, Fe, Co, and La similar to National Bureau of 

Standards (NBS) standard coal 1632, because the 

gamma-rays from the activation products of these elements dominate the spectrum of most activated coal 

samples and limit the sensitivities for the determinations 

of other elements. 

The pertinent information for the short-lived species that can be measured for the determination of nine 

additional elements is listed in table 8. Those species 

with half-lives of less than 1 h are generally measured 

after irradiation for 5 min at a flux of 3 x 1012 units in 

the pneumatic tube system of the U.S. Geological 

Survey 1 MW TRIGA reactor in Denver, Colo., and 

counted after approximately 10 min of decay. Manganese and dysprosium are measured after a 2 h irradiation and approximately 3 h of decay. 

28 Methods for Sampling and Inorganic Analysis of Coal 

EXPERIMENTAL METHODS AND PROCEDURES 

Sample Preparation 

The TRIGA research reactor facility of the U.S. 

Geological Survey is utilized for most of the INAA work 

conducted in our laboratories. Powdered samples, weighing 500 mg, are heat sealed in 1.5-cm3 polyethylene vials. 

Eighty samples, including standards, can be irradiated 

in the "lazy susan" facility of the reactor for 8 hat a flux 

of 6 x 1012 n/ cm2 s. The samples are packaged in 7 .4-cm3 

snap-top polyethylene vials and inserted into a single 

TRIGA tube in the "lazy susan." Because of a modest 

flux variation along the tube, the 40 samples and 

standards on each level are treated as separate sample 

sets during the subsequent counting and data processing 

procedures. 

Samples, as small as 2 mg, can be analyzed after 

irradiation in the U.S. Geological Survey TRIGA reactor by increasing the irradiation time to 16 or 24 h. The 

sensitivity is reduced for the determination of several 

elements in samples weighing less than 200 mg, and less 

than 20 elements can be detected for most samples 

weighing less than 10 mg. 

Standards 

Three multiple-element standards, or flux monitors, are currently used for the routine analysis of coal: 

NBS 1632 (coal) and 1633 (fly ash) and Eastman-
Table 7. Long-lived ( >1 0 h) radionuclides 

Limit of Potential Spectral Interferences 

Determination 

Indicator Preferred ppm (p,g/g) except RadioElement Radionuclide Half-life 'Y -energy % (cg/g) as indicated Radio-nuclide Energy nuclide Energy 

Na 24Na 15.0 h 1368.6 10 

2753.9 

K 42K 12.4 h 1524.7 0.01 OJo 

Sc 46Sc 84 d 1120.5 0.01 

Cr 5ICr 27.8 d 320.1 0.5 I77Lu 321.3 I47Nd 319.4 

Fe 59Fe 45.6 d 1099.3 50 1s2Ta 1289.1 

1291.5 75 

Co 6oco 5.3 yr 1173.2 0.2 

1332.5 0.2 

Zn 6szn 245 d 1115.4 1 I6oTb 1115.1 

Ga 72Ga 14.1 h 834.1 0.1 54Mn 834.8 

As 76As 26.4 h 559.0 0.1 

Se 75Se 120.0 d 264.6 0.1 1s2Ta 264.1 

Br s2Br 35.4 h 554.3 0.5 

776.5 0.5 

Rb s6Rb 18.7 d 1076.8 5 

Sr sssr 64.0 d 514.0 50 

Zr 95Nb 35.1 d 765.8 200 1s2Eu 764.8 I6oTb 765.3 

9szr 65.0 d 756.7 200 I54Eu 756.8 

Mo 99Mo 66.7 h 140.5 10 

Sb 122Sb 67.2 h 564.0 0.05 

I24Sb 60.0 d 1691.0 0.1 

Cs I34Cs 2.1 yr 795.8 0.1 

Ba IOIBa 12.0 d 496.3 100 I03Ru 497.0 

La I4oLa 40.2 h 1596.6 0.02 

487.0 0.05 

Ce I4ICe 32.5 d 145.4 0.5 I54Eu 145.6 

Nd I47Nd 11.1d 531.0 2 

Sm I53Sm 46.8 h 103.2 0.5 239Np 103.7 

Eu 1s2Eu 12.7 yr 779.1 0.04 

1408.1 0.01 

Tb I6oTb 72.1 d 298.6 0.05 233pa 299.9 

1178.1 0.1 

Yb nsyb 101.0 h 396.1 0.1 I47Nd 398.2 233pa 398.2 

282.6 0.2 

Lu I77Lu 6.7 d 208.4 0.01 239Np 209.7 

Hf I81Hf 42.5 d 482.2 0.1 

133.1 0.05 

Ta 1s2Ta 115.1 d 1221.3 0.02 

1189.2 0.03 

w 1s7w 24.0 h 479.5 0.1 

685.7 0.1 I47Nd 685.9 

Hg 2o3Hg 46.6 d 279.2 0.1 75Se 279.5 

Th 233pa 27.0 d 311.9 0.1 

u 239Np 2.3 d 277.6 0.5 

The Determination of 41 Elements in Whole Coal by Instrumental Neutron Activation Analysis 29 
Table 8. Short-lived indicator radionuclides 

Preferred Limits of Potential Spectral 

Indicator Half- )'-energy Determination Interferences 

Element Radionuclide life (keV) (keV) 

tY2 > 1 h, < 3 h 

Mn 56Mn 2.58 h 846.7 

1811.2 

Dy t6sDy 2.36 h 94.7 0.1 

tY2 < 1 h 

Mg 27Mg 9.5 min 844.0 1 OJo s6Mn 846.7 

1014.1 

AI 2sAI 2.27 min 1778.9 50 

s 37s 5.04 min 2081.8 1% 

3103.8 

Cl 3sCI 37.3 min 1642.0 100 

Ca 49Ca 8.8 min 2062.5 0.5% 

Ti stTi 5.8 min 320.1 0.1% 

v s2v 3.76 min 1434.0 50 

Kodak gelatin multicomponent reference material 

(TEG-50-B). The concentration values used for NBS 

1632 and 1633 are those of Ondov and others (1975). 

Standard TEG-50-B has been calibrated against singleelement standards for As, Co, Cu, Hg, Sb, Se, and Zn. 

In addition, NBS standard reference materials 1632a 

and 1633a have been characterized in the U.S. Geological Survey laboratories for use as standards. Data for 

-all five standard samples are listed in table 9. Antimony 

has been observed to be inhomogeneous in NBS 1632 

(Ondov and others, 1975) and has a low concentration in 

NBS 1633. Thus, TEG-50-B is used as a standard for 

antimony. For short irradiations, these standards are 

supplemented with analytical-grade sulfur and spectroscopic grade CaC03 and MgO. Recently, work has 

begun on a new U.S. Geological Survey standard that 

will consist of a spiked coal from the Lower Bakerstown 

coal bed. After testing of this standard is complete, the 

NBS standards will probably be used only for qualitycontrol purposes. 

Counting Facilities 

Following an 8-h irradiation in the U.S. Geological Survey reactor in Denver, Colo., and the subsequent 

four days of transcontinental shipping of the samples, 

all samples are placed in 7 .4-cm3 polyethylene vials. 

These vials serve as transfer containers for the automatic 

sample changers used with the high-resolution coaxial 

Ge(Li) detectors for gamma-ray spectroscopy. The detectors are coupled to multichannel pulse-height analyzers, 

which are capable of dividing the spectrum into 4,096 

energy increments or channels. The analyzers automatically repeat a cycle of data acquisition, sample changing, and read-out of the spectral data to disk storage. 

The automatic sample changer used with each detector is 

mechanically identical to that described by Massoni and 

30 Methods for Sampling and Inorganic Analysis of Coal 

others (1973), but the electronic interface has been 

completely redesigned to employ solid-state circuitry. 

Eight sample changers are controlled by a single interface. At the end of each preset counting period, the 

multichannel analyzer signals the controller to change 

samples. The sample changer is a gravity feed device that 

uses compressed air to eject a sample from the counting 

station after counting is completed. 

Data Reduction 

All spectra are processed using the computer 

program SPECTRA (Baedecker, 1976, 1980; Grossman 

and Baedecker, 1986). The program contains algorithms 

for smoothing the spectral data; searching out all peaks 

in the spectrum; determining the areas of both wellresolved, single peaks and unresolved (or overlapping) 

multiple peaks; and determining the energies of the 

photopeaks (including corrections for zero and gain 

drift of the spectrometer). The calculations of elemental 

concentrations include corrections for spectral interferences, decay, and neutron-flux variations, as well as 

pulse pileup effects. When a gamma-ray line has been 

specified for use in the analysis and has been observed in 

a standard material but not in a sample, the program 

computes an upper limit to the concentration of the 

element in question. The peak area used for the calculation is 10 times the standard deviation of the background within the normal integration limits at the 

expected peak location in the spectrum. The program 

corrects for overlapping spectral lines that are too 

poorly resolved to be recognized as multiplets when an 

interference-free line of the interfering radionuclide can 

be observed in the spectrum and used for correction. For 

example, the area of the 264.6-keV line of 75Se can be 

corrected for interference from the 264.1-keV line of 

182Ta. This correction is accomplished by using the peak 

area of the 1221.3-keV line of 182Ta and the known ratio 

of the intensity of the 264.1-ke V line to the intensity of 

the 1221.3-keV line. 

Thus, elemental concentration data, based on each 

specified peak, are stored in a disk file that is generated 

during execution of the SPECTRA program. A second 

program, SUMMARY I, is executed after the successful 

execution of SPECTRA, to average the results from 

multiple lines for a given element and to generate a 

report of analysis for a single counting of a sample set. 

Peaks that are averaged are specified to the program in 

order of decreasing priority. Results from lower-priority 

peaks are included in the reported result only if they 

agree within 2 standard deviations of the mean based on 

the peak(s) given higher priority. Each result included in 

the mean is weighted by its estimated standard deviation 

based on counting statistics. The weighted average results 

and the estimated standard deviations for each element 

are stored in a disk file for long-term storage. 
Table 9. Concentrations of 40 elements in multiple-element standards used for the analysis 

of coal (J.tg/g, unless percent indicated) 

[Sulfur was not included because it was below the detection limit for all these standards, and elemental sulfur 

was used as a standard. j 

Standards 

Element 1632* 1632a 1633* 1633a TEG-50-B 

Na 414 ± 20 90 ± 1 3200 ± 400 2000 ± 100 397 ± 5 

Mg OJo 0.20 ± 0.05 1.8 ± 0.4 

AI% 1.85 ± 0.13 12.7 ± 0.5 

Cl 890 ± 125 42 ± 10 

K% 0.28 ± 0.03 0.40 ± 0.02 1.61 ± 0.15 2.1 ± 0.3 

Ca% 0.43 ± 0.05 4.7 ± 0.6 

Sc 3.7 ± 0.3 6.0 ± 0.1 27 ± 1 41.8 ± 0.4 

Ti 1040 ± 110 7400 ± 300 

v 36 ± 3 235 ± 13 

Cr 19.7 ± 0.9 32.4 ± 0.4 127 ± 6 212 ± 6 47 ± 3 

Mn 43 ± 4 496 ± 19 

Fe 0.84 ± 0.04 1.09 ± 0.02 6.2 ± 0.3 10.4 ± 0.2 

Co 5.7 ± 0.4 6.2±0.18 41.5 ± 1.2 44.5 ± 0.5 46 ± 2 

Zn 30 ± 10 30 ± 2 216 ± 25 260 ± 15 53± 4 

Ga 5.8 ± 0.4t 7.0 ± 0.05 40.7 ± 1.2t 

As 6.5 ± 1.4 9.6±0.1 58± 4 177 ± 4 105 ± 5 

Se 3.4 ± 0.2 2.35 ± 0.05 10.2±1.4 10.9 ± 0.9 43 ± 3 

Br 19.3 ± 1.9 44 ± 1 12 ± 4 7.8 ± 0.6 

Rb 19.4 ± 2.3t 110 ± 9t 

Sb 3.9 ± 1.3 0.61 ± 0.03 6.9 ± 0.6 6.2 44 ± 4 

Sr 161 ± 16 88 ± 6 1700 ± 300 940 ± 40 

Zr 301 ± 20 

Mo 3.1 ± 0.1t 25 ± 2t 

Cs 1.4 ± 0.1 2.1±0.5 8.6 ± 1.1 11.0 ± 0.3 

Ba 352 ± 30 127 ± 8 2700 ± 200 1500 ± 60 

La 10.7 ± 1.2 15 ± 7 82 ± 2 94 ± 1 

Ce 19.5 ± 1 28 ± 1 146 ± 15 184 ± 8 

Nd 8.7 ± 1.0t 12 ± 1 57.8 ± 1.6t 79 ± 3 

Sm 1.7 ± 0.2 2.0 ± 0.1 12.4 ± 0.9 14 ± 2 

Eu 0.33 ± 0.04 0.49 ± 0.01 2.5 ± 0.4 3.9 ± 0.1 

Tb 0.23 ± 0.05 0.31 ± 0.01 1.9 ± 0.3 2.8 ± 0.2 

Dy 1.12 ± o.o6t 9.4 ± o.5t 

Yb 0.7±0.1 1.2 ± 0.1 7 ± 3 9.2 ± 0.2 

Lu 0.14 ± 0.01 0.15 ± 0.01 1.0±0.1 1.2 ± 0.1 

Hf 0.96 ± 0.05 1.23 ± 0.02 7.9 ± 0.4 6.5 ± 0.1 

Ta 0.24 ± 0.04 0.41 ± 0.01 1.8 ± 0.3 2.4 ± 0.1 

w 0.75 ± 0.17 0.76 ± 0.03 4.6 ± 1.6 5 ± 1 

Hg 0.22 ± 0.03 60 ± 5 

Th 3.2 ± 0.2 4.3±0.1 24.8 ± 2.2 27.5 ± 5 

u 1.41 ± 0.07 1.3±0.1 12.0 ± 0.5 11.4±0.3 

* From Ondov and others (1975) (except as noted). 

t From Rowe and Steinnes (1977 a). 

Errors based on standard deviation of 12 replicates. 

The Determination of 41 Elements in Whole Coal by Instrumental Neutron Activation Analysis 31 
Following the completion of all counts on each set 

of samples during a 2-month decay period, a third 

program, SUMMAR Y2, is executed to average the 

results from multiple counts and to generate a report of 

analysis. Again, the mean value for each element is a 

weighted mean based on the estimated counting error. If 

uranium has been determined via the 2.35-day 239Np, 

SUMMARY2 corrects for fission product interferences 

in the determination of Zr, Mo, La, Ce, Nd, and Sm 

using the correction factors listed in table 10. Where the 

magnitude of the correction exceeds 20 percent of the 

value reported, the value is flagged in the report of 

analysis. The calculation of the fission product interference for lanthanum is complicated by the fact that the 

fission product 140Ba has a longer half-life (12. 7 days) 

than its daughter product, the indicator radionuclide 140La. We have not measured the fission product interference for lanthanum at the normal decay time of 6 

days for coal samples. We use the calculated value of 

0.02 part per million of lanthanum per part per million 

of uranium for computing the fission product interference, which is generally less than 1 percent for most coal 

samples. The experimental values for other elements 

listed in table 10 are not decay dependent and were 

measured at a decay time of 10 days after irradiation. 

Because the experimental values agree with the calculated values to within 25 percent and the fission product 

interferences for most coals are below 2 percent, small 

errors in the interference-correction factor result in 

negligible errors in the data. 

Quality Control 

An estimate of the precision for each sample set is 

made by using replicate samples to determine the reproducibility of the measurements. Several replicate samples are generally determined within each sample set. In 

addition, many elements are determined by two or more 

counting cycles. 

Agreement in both cases is usually within errors 

determined by counting statistics. When this is not the 

case, the results are flagged in the data reduction 

procedures using programs described by Grossman and 

Baedecker (1986). An estimate of the accuracy of the 

data is obtained by running control standards that can 

then be compared to "best values" determined from the 

literature or from previously determined averages. Reference materials 1632a and 1633a are most commonly 

used as control standards. "Best values" for these are 

given in table 9. This procedure also allows for an 

estimate of the precision of the data between different 

sample sets. Computerized procedures (including 

graphic presentation of the quality-control data) for 

comparing measured values with "best values" were also 

described by Grossman and Baedecker (1986). 

32 Methods for Sampling and Inorganic Analysis of Coal 

Table 10. Interferences in INAA due to neutron-induced 

fission of 235U (in 11g of the elements (apparent) per 11g of U) 

Fission (n, -y) Cross 

Isotope Yield Section (barns) I (calc.)* I (exp.)* 

9szr 6.5 0.08 7.5 11.5 ± 0.3 

99Mo 6.1 0.51 0.85 1.01 ± 0.13 

14oLa 6.3 8.9 0.020t 

141Ce 5.9 0.6 0.27 0.29 ± 0.01 

147Nd 2.26 2 0.17 0.22 ± 0.01 

1s3Sm 0.16 210 0.00008 

* Error estimates are 70 percent confidence limits on the mean of 

four determinations. 

t 6 days following irradiation. 

* Calculation assumes that the cross section for fission of 235U is 

equal to 580 barns. 

DISCUSSION 

Up to 41 elements can be determined in coal and 

fly ash by a combination of short and long irradiations 

for INAA. Except for dysprosium, all the elements 

determined using short-lived indicator radionuclides are 

light or first-row transition elements, which can be better 

determined by other multiple-element instrumental techniques. The use of short irradiations and counting times 

is primarily useful for the analysis of small samples 

where it is desirable to get as complete an analysis as is 

possible on a single sample (e.g., mineral, size, or 

density separates). Of the elements with half-lives of less 

than 1 h, the lines from the activation products of Mg, 

Al, and V are most readily observed in the spectra 

obtained within 10 min of irradiation. The remaining 

four elements listed in table 8 (S, Cl, Ca, and Ti) are 

determinable with a detectability poorer than that for 

Mg, AI, and V. 

The following discussions provide more detailed 

evaluations of the problems associated with the determination of specific elements. 

Sulfur is determined in the short counting cycle, 5 

min after irradiation. It is determined from the reaction 

36s + n - 37s + 'Y 

t y2 5 07 . 37S = . mm 37Cl + {3 + 'Y 

The determination of sulfur is subject to error due to 

natural variation in the isotopic abundance of 36S. A 

maximum error of ±29 percent has been calculated, but 

errors from + 4.4 to -6.5 percent have been observed 

for results on natural material when compared with a 

standard with o 34S = 0. Because of the low natural 

abundance of 36S (0.01 percent) and its low cross section 

(0.14 b), the determination of sulfur has poor sensitivity, and errors from counting statistics are likely to be 

much higher than errors in isotopic composition for 

most moderate- to low-sulfur coals. 
Although the concentration of magnesium is moderately high in most coal samples, it is relatively difficult 

to measure, because 27Mg is produced in the reactor 

from two sources: from the (n, ')')reaction or 26Mg and 

from the (n, p) reaction or 27 AI. Because most coal 

samples having high magnesium concentrations commonly have even higher aluminum concentrations, large 

corrections must be made. The correction, which 

depends on the neutron spectrum for a given reactor, is 

about 35 percent for NBS 1632 irradiated in the 

pneunmatic tube of the U.S. Geological Survey Denver 

reactor. 

The accuracy for the determination of gallium is 

greatly dependent on concentrations of iron and the 

speed with which the sample is counted. The major 

photopeak of 31Ga (834 keV) has an interference from 

the 835-keV photopeak of 54Mn that is formed from the 

(n, p) reaction of 54Fe. Although the 54Fe peak is 

relatively small for most coal samples, the half-life of 

gallium is only 14 h. For samples having high concentrations of iron or a large counting delay, this interference can be a major problem. For NBS 1632, the relative 

error is 1.2 percent after 3 days, but the error increases 

to 70 percent after 6 days. 

The determination of chromium suffers from 

potential spectral interference from 177Lu and 147Nd. 

For NBS 1632, the corrections for these interferences 

amount to :51 percent, but they can be higher in coals 

with lower concentrations of chromium or higher contents of the lanthanide elements. 

The 1,115-keV photopeak of 65Zn falls on the 

low-energy tail from the 1,120-keV photopeak from 46Sc, which complicates the evaluation of the base area 

for the photopeak. This 65Zn photopeak is normally 

treated by the computer algorithm as part of a triplet 

along with the 1,112-keV photopeak of 152Eu. Also, a 

small interference exists from 160Tb, which amounts to 

1 percent zinc in NBS 1632. 

The 264.6-keV photopeak from selenium is best 

measured in coal samples in a count taken from 3 weeks 

to 2 months after irradiation. A correction must generally be made for an interference from 182Ta. The 

correction is 8 percent of the measured selenium in NBS 

1632. 

Zirconium is difficult to determine by INAA due 

to spectral interferences from 152Eu, 154Eu, and 160Tb, 

which interfere with the lines from 92Zr and its daughter 

product, 35.1-day 95Nb. For NBS 1632, the correction 

on the 95Nb 765.8-keV line is 10 percent. Also, a 

correction is necessary for the fission product interference based on the measured uranium content, which for 

fly ash NBS 1632 amounts to 45 percent. For these 

reasons, the determination of zirconium is semiquantitative at best. 

Molybdenum, like zirconium, falls near the lowmass maximum of the fission yield curve of 235U, and a 

large fission-interference correction is generally required. 

The interference correction would be roughly 46 percent 

of the value for NBS 1632 and 1633. 

The determination of barium is based on the 

measurement of the most intense 131Ba line at 496.3 keV 

in the Ge(Li) spectrum taken within a week of irradiation. There is a potential spectral interference from 

fission product 103Ru, which cannot be corrected because 

of the absence of any other interference-free line from 103Ru of sufficient intensity. An estimate of the interference calculated from fundamental parameters and confirmed by experiment is 2.9 x e0 ·

0402 t (apparent parts per 

million of barium per part per million of uranium), 

where t is the time after irradiation in days. For NBS 

1632, 103Ru contributes 1.5 percent to the intensity of 

the barium photopeak seven days after irradiation, and 

for NBS 1633, it contributes 1.7 percent. 

The determination of lanthanum also can be 

affected by fission product interferences. The measurement is complicated by the relatively long lived, 12.8-day 140Ba, which is a fission product precursor to the 

indicator radionuclide 140La. Four days after irradiation, the interference from 140Ba is 0.0084 (apparent 

parts per million of lanthanum per part per million of 

uranium), or a 0.1-percent correction for NBS 1632. For 

later counts, the correction will increase; at a counting 

time of 10 days, the interference is 0.092, or a 1.2-

percent correction for NBS 1632. 

The determination of terbium is made difficult by 

spectral interferences. The most intense line in the 

Ge(Li) spectrum, at 298.6 keV, occasionally suffers 

from interferences from the 233Pa 299.9-keV line. The 

computer program must first check to see if both lines 

have been detected and resolved by the multiplet analysis 

algorithm; if not, the program then applies a correction 

for the interference, which for NBS 1632 will be 50 

percent, at a decay time of two months. The 879.4-keV 

line is also observed in most spectra as a weak line on the 

low-energy tail of the generally intense 146Sc 889.3-keV 

line, which renders the base area difficult to evaluate. 

The 965.8-keV line may suffer from interference from 152Eu, and while the 1,177.9-keV line is free from 

interferences, it has much poorer sensitivity. 

Photopeaks from 101-h 175Yb and 32-day 169Yb 

are normally detected in Ge(Li) spectra of activated 

coal. Most photopeaks from both nuclides incur spectral interferences, although ytterbium is generally well 

determined using the 396.1-keV line of the shorter-lived 

isotope. There are minor interferences from 147Nd and 233Pa; the correction is 3 percent for NBS 1632. 

Mercury can be determined in many coal samples 

by measuring the intensity of the 279.2-keV line of the 

46.6-day 203Hg. A substantial spectral-interference correction is generally required due to 75Se (60 percent for 

NBS 1632). Because the 175Se 264.6-keV line, which is 

used to make the correction, suffers from a generally 

The Determination of 41 Elements in Whole Coal by Instrumental Neutron Activation Analysis 33 
small interference from 182Ta, the algorithm must treat 

the 264.6-keV line before computing a mercury content 

from the 279.2-keV photopeak. 

Rowe and Steinnes (1977a, b) have described the 

application of epithermal neutron irradiations to the 

analysis of coal. Many of the spectral and fission 

product interferences discussed in this section can be 

reduced and greater sensitivity realized by this technique, particularly for the determination of Ni, Mo, Rb, 

Sr, Cs, Tb, Ta, W, and U. However, the technique is 

limited to small (-50 mg) samples and requires special 

packaging in aluminum foil and irradiation inside cadmium capsules. Because of the added cost and labor 

involved in the special handling of samples for epithermal neutron activation analysis (and increased radiological hazard of handling radioactive coal powders), the 

technique is not suitable for routine application but is 

useful for special problems. 

REFERENCES 

Baedecker, P.A., 1976, SPECTRA: computer reduction of 

gamma-ray spectroscopic data, in Taylor, R.E., ed., 

Advances in obsidian glass studies: Park Ridge, New 

Jersey, Noyes Press, p. 334-349. 

-- 1980, Comparisons of peak-search and photopeakintegration methods in the computer analysis of gammaray spectra, in Vogt, J .R., ed., International Conference 

34 Methods for Sampling and Inorganic Analysis of Coal 

on Nuclear Methods in Environmental and Energy 

Research, 4th, 1980, Proceedings: U.S. Department of 

Energy CONF-800433, p. 15-24. 

Block, C., and Dams, R., 1973, Determination of trace 

elements in coal by instrumental neutron activation analysis: Analytica Chimica Acta, v. 68, no. 1, p. 11-24. 

Grossman, J.N., and Baedecker, P.A., 1986, Computer 

graphics for quality control in the INAA of geological 

samples, Proceedings: Modern Trends in Activation 

Analysis, Copenhagen, Denmark, June 23-27, 1986, p. 

571-578. 

Massoni, C.J., Fones, R.V., and Simon, F.O., 1973, A 

pneumatic sample changer for gamma-ray spectroscopy: 

Review of Scientific Instruments, v. 44, no. 9, p. 

1350-1352. 

Ondov, J.M., Zoller, W.H., Olmez, Ilhan, Aras, N.K., 

Gordon, G.E., Rancitelli, L.A., Abel, K.H., Filby, R.H., 

Shah, K.R., and Ragaini, R.C., 1975, Elemental concentrations in the National Bureau of Standards' environmental coal and fly ash standard reference materials: 

Analytical Chemistry, v. 47, no. 7, p. 1102-1109. 

Rowe, J.J., and Steinnes, E., 1977a, Determination of 30 

elements in coal and fly ash by thermal and epithermal 

neutron-activation analysis: Talanta, v. 24, p. 433-439. 

-- 1977b, Instrumental activation analysis of coal and fly 

ash with thermal and epithermal neutrons: Journal of 

Radioanalytical Chemistry, v. 37, no. 2, p. 849-856. 

Swaine, D.J., 1985, Modern methods in bituminous coal 

analysis: Trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 315-346. 
THE DETERMINATION OF MAJOR AND MINOR 

ELEMENTS IN COAL ASH AND OF CHLORINE AND PHOSPHORUS IN 

WHOLE COAL BY X-RAY 

FLUORESCENCE SPECTROMETRY 

By R.G. Johnson, G.A. Sellers, and S.L. Fleming, II 

Abstract 

Methods for the X-ray fluorescence spectrometric analysis of 11 elements in coal ash (Na, Mg, AI, Si, P, S, K, Ca, Ti, 

Mn, and Fe) and of two elements in whole coal (CI and P) are 

described. Coal-ash samples are fused with lithium tetraborate 

to produce glass disks; whole-coal samples are briquetted 

with a cellulose binder prior to analysis. Calibration for all 

elements in both whole coal and coal ash is accomplished by 

using a simple linear regression of X-ray intensity versus 

concentration. Silicate rock standards are used for calibration 

in coal ash analysis, and whole-coal analyses are based on 

coal standards from the National Bureau of Standards (NBS), 

on coals analyzed by independent methods, and on synthetic 

standards. Precision, expressed as the relative standard deviation, is 2 to 5 percent for coal ash and 10 percent for 

determinations of elements in the whole coal. 

INTRODUCTION 

X-ray fluorescence (XRF) spectrometry is a rapid 

technique for accurate and precise elemental analysis of 

solid and liquid specimens. As such, it is suited to the 

determination of certain important elements that occur 

in coal and has been used extensively for the analysis of 

both whole coal and coal ash (Kuhn and others, 1975; 

Giauque and others, 1979; Mills and others, 1981; 

Wheeler, 1983). In practice, most XRF spectrometer 

systems are not able to detect elements having atomic 

numbers lower than 11, the atomic number of sodium. 

Thus, concentrations of the most abundant elements in 

the coal matrix (C, H, N, and 0) must be determined by 

other methods. 

In general, the accuracy of XRF spectrometric 

determinations of inorganic elements depends on concentration, particle size, matrix effects, surface roughness, the quality of standard materials, and other related 

factors. The accuracy of analysis usually falls between 2 

and 10 percent (relative) depending on how well these 

factors have been controlled. The lower limit of determination is as low as 1 11g/ g for elements having atomic 

numbers greater than 26, the atomic number of iron, 

and ranges to several hundred micrograms per gram for 

aluminum and silicon and to several thousand micrograms per gram for sodium. The upper limits for 

quantitative XRF spectrometric analysis are determined 

by the availability of standard reference materials. 

This section describes procedures for the analysis 

of 2 minor elements (Cl and P) in whole-coal samples, 

and 11 major elements (Na, Mg, AI, Si, P, S, K, Ca, Ti, 

Mn, and Fe) in the corresponding high-temperature (525 

°C) coal ash. 

EXPERIMENTAL METHODS AND PROCEDURES 

Equipment and Supplies 

The instruments and reagents required in the XRF 

spectrometric methods are listed here. 

1. For the preparation of a coal-ash fusion disk the 

following items are required. 

Analytical balance 

Automatic fluxer 

Pt-Au crucibles and 

molds (95 percent Pt 

alloyed with 5 percent 

Au) 

Lithium tetraborate 

1-mg sensitivity 

Corporation Scientifique 

Claisse, Quebec, Canada 

Johnson Matthey, Inc. 

Seabrook, NH 

Spectroflux 100 

Johnson Matthey, Inc. 

Seabrook, NH 

The Determination of Major and Minor Elements in Coal by X-ray Fluorescence Spectrometry 35 
Storage desiccators 

2. For the preparation of whole-coal briquettes the 

following items are required. 

Analytical balance 

Mixer-mill and 

accessories 

Cellulose powders 

Hydraulic press 

1-mg sensitivity 

Spex Industries 

Whatman microgranular 

(CC-31), Whatman 

fibrous (CF-1) 

276 MPa (40,000-psi) 

capacity, minimum 

3. Standard reference materials can be obtained from 

the National Bureau of Standards (NBS), Office of 

Standard Reference Materials, Room B311, Chemistry Building, Gaithersburg, MD 20899. 

Coal Ash 

Because coal ash represents the dominant mineral 

portion of coal, XRF spectrometric analysis of this 

material is very similar to the XRF analysis of silicate 

rocks (Rose and others, 1963; Norrish and Hutton, 

1969). Samples are prepared by fusion with lithium 

tetraborate flux, and silicate rock standards are used to 

construct calibration curves for each element. Extensive 

matrix correction techniques are not required because of 

the almost eightfold dilution of the sample by the flux. 

Fusion is the preferred method of preparation because it 

eliminates particle-size effects and mineralogical heterogeneity and thus allows for the highest precision possible. 

A sample is prepared by thoroughly mixing 600 

mg of coal ash with 5.400 g of lithium tetra borate in a 

Pt-Au crucible (95 percent Pt and 5 percent Au). To this 

mixture is added 5 drops of a 15-percent hydrobromic 

acid solution, which acts as a nonwetting agent during 

the fusion. Samples are fused for 20 min by a commercial fluxer (ClaisseR) that produces a temperature in the 

range of 1, 100 to 1 ,200 o C. Alternatively, samples may 

be fused for 1 hat 1,100 oc by a U.S. Geological Survey 

"in-furnace" device (Taggart and Wahlberg, 1980a), and 

finally cast in Pt-Au molds (Taggart and Wahlberg, 

1980b) to produce glass disks. Caution is advised here. 

Preliminary evidence indicates that the higher temperature effected by the Meeker burner in the ClaisseR fluxer 

may volatilize sodium from certain samples during the 

fusion process. 

A DianoR model XRD-8300 wavelength-dispersive 

XRF (WDXRF) spectrometer is used to make all intensity measurements; instrumental parameters and operating conditions are listed in table 11. 

Calibration of the instrument consists of plotting 

X-ray intensity versus concentration of the standard 

36 Methods for Sampling and Inorganic Analysis of Coal 

Table 11. Instrumental operating conditions for XRF 

analysis of coal ash 

Element Anode kV mA Crystal 

Na Cr 60 33 Ovonyxa 

Mg Cr 60 33 Ovonyx 

AI Cr 50 40 PET 

Si Cr 50 40 PET 

p Cr 50 40 Ge 

s Cr 50 40 PET 

K Cr 50 10 LiF(200) 

Ca Cr 50 10 LiF(200) 

Ti Cr 50 30 LiF(200) 

Mn w 50 40 LiF(200) 

Fe w 50 10 LiF(200) 

a The Ovonyx crystal is a synthetic multiple-layer structure with 

a d-spacing of 2.28 nm. 

reference materials for each element and calculating 

slope and intercept through simple linear regression 

analysis. Silicate rock standards are used for every 

element except sulfur because of their availability and 

similarity to the composition of most coal ashes. The 

ranges of concentration (Abbey, 1983) covered by these 

reference materials for 10 elements (excluding sulfur) 

are listed in table 12. Results from a typical calibration 

for iron are shown in table 13 in the form of accepted 

and calculated concentrations generated by the simple 

linear regression model. 

Because many coal ashes contain much higher 

levels of sulfur than do the available reference materials, 

the preparation of separate standards for use in determining sulfur is necessary. To prepare these standards, a 

typical rock standard is spiked with sulfur and diluted in 

steps with the unspiked material to produce a set of 

secondary standards covering the intended concentration range. The mixture is fused with lithium tetraborate 

flux, and sulfur in the product is determined by an 

independent method (LECOR sulfur analyzer) because 

some sulfur is lost during the fusion process. 

Table 12. Concentration ranges provided by rock standards 

for the XRF analysis of coal ash 

Oxide 

Na20 

MgO 

Al20 3 

Si02 

P20s 

K20 

CaO 

Ti02 

MnO 

Fe20 3 

Concetration (percent) 

Lowest standard Highest standard 

0.06 

0.10 

0.73 

4.43 

0.01 

0.03 

0.08 

0.01 

0.01 

1.00 

8.37 

43.50 

54.53 

87.21 

34.50 

10.03 

50.50 

2.69 

0.77 

25.76 
Table 13. XRF calibration of iron in coal ash: simple linear 

regression analysis results 

Standard 

AGV-1 

DNC-1 

W-1 

QL0-1 

G-1 

ANY 

SC0-1 

SDC-1 

ANQ 

ANY 

BCR-1 

BHV0-1 

GSP-1 

STM-1 

W-2 

CRPG-Fe 

G-2 

RGM-1 

ANW 

ANX 

BIR-1 

Concentration (percent) 

Accepted 

6.78 

9.85 

11.11 

4.29 

1.94 

7.48 

5.22 

6.85 

2.26 

13.85 

13.41 

12.23 

4.30 

5.20 

10.77 

25.76 

2.69 

1.89 

5.33 

4.25 

11.25 

Calculated 

6.83 

9.72 

10.90 

4.15 

1.49 

7.56 

5.47 

7.27 

2.10 

14.19 

13.73 

12.07 

4.05 

5.47 

10.97 

24.92 

2.36 

1.55 

5.51 

4.37 

11.45 

The sulfur reference standards used for this work 

were produced by spiking U.S. Geological Survey basalt 

BIR-1 with ignited calcium sulfate. Serial dilutions of 

this mixture with BIR-1 were made to cover the concentration range of 0.1 to 10 percent sulfur. Samples were 

prepared in duplicate, and one of each was crushed, 

ground, and analyzed by a LECOR sulfur analyzer. 

Calibration for sulfur is accomplished in the same way 

as the calibrations for other elements. 

The XRF spectrometric determinations of major 

elements in coal ash compare well with other analytical 

methods. Because the chemistry (or at least the range of 

composition of the major elements) of coal ash is similar 

to that of silicate rocks, the accuracy is approximately 

the same. This accuracy is estimated to be ±2 to 5 

percent (relative error) depending on the element and the 

concentration level. 

Whole Coal 

One advantage of analyzing whole coal is that 

volatile elements normally lost in ashing or fusion can be 

determined. The analysis of whole coal may include 

practically any element, at concentrations approaching 

1 /J-g/g for many. One problem, however, is that calibration standards for XRF spectrometric analysis of whole 

coal must themselves be whole coals. Only a few coal 

standards exist, and these are certified for only a few 

elements. Thus, additional reference materials must be 

established by analysis of existing coals by other methods or by preparation of synthetic standards. 

Specimen preparation normally involves grinding 

a coal sample with a binder, followed by compression to 

form a briquette. A low weight-ratio of sample to binder 

is used because the XRF spectrometric analysis of whole 

coal usually involves the determination of certain trace 

elements for which the best possible detection limits are 

desired. This section describes procedures used in the 

determination of phosphorus and chlorine in whole 

coal. Similar procedures could be used for the determination of other elements. 

Air-dried coal samples (80 mesh) to be prepared 

for XRF analysis are further dried for three hours at 105 

°C. Then, 0.500 g of coal is mixed with an equal portion 

of micro granular cellulose that serves as a binder. The 

mixture is transferred to a 26-mL polystyrene vial 

containing two 6-mm-diameter polycarbonate beads (to 

aid mixing) and is shaken on a mixer-mill for 10 min to 

ensure homogeneity. This mixture is pressed against an 

equal volume of fibrous cellulose (to provide a strong 

backing) in a hydraulic press at 276 MPa (40,000 psi) for 

30 s to produce a 2.54-cm-diameter briquette. 

Measurements are made by a DianoR model XRD8300 WDXRF spectrometer; instrumental operating conditions are listed in table 14. 

Table 14. Operating conditions for XRF analysis of whole 

coal 

Element 

p 

Cl 

Anode 

Cr 

Cr 

kV 

50 

50 

mA 

40 

40 

Crystal 

Ge 

PET 

Standards used for the determination of chlorine 

and phosphorus in whole coal include three NBS reference materials, coals that have been analyzed by other 

methods, and synthetic standards. The NBS coal standards include NBS 1633, 1633a, and 1635. NBS 1633 is 

no longer available, and NBS 1632b has only recently 

become available. The NBS coals are used in determinations of both chlorine and phosphorus; concentration 

values are taken from Germani and others (1980) and 

from Ondov and others (1975) because the concentrations of these elements are not certified by NBS. 

Standards for the determination of chlorine in 

whole coal consist of a set of coals from three power 

plants. These coals were analyzed by instrumental neutron activation analysis (R.B. Finkelman, written commun., 1980) for 18 elements, including chlorine. A 

second set of five coals was the subject of an American 

Society for Testing and Materials (ASTM) cooperative 

program investigating XRF analysis of whole coals 

(ASTM D.05.29.02); although the coal samples were not 

intended to be distributed as standards, they were extensively analyzed by a variety of methods for the 10 major 

elements and phosphorus. 

The Determination of Major and Minor Elements in Coal by X-ray Fluorescence Spectrometry 37 
Finally, when the available standard reference 

material is not sufficient to meet analytical needs, it is 

possible to produce synthetic standards. The use of 

synthetic standards is the least desirable alternative 

because of the uncertainty in the composition of the 

final product due to preparation error and the considerable time and effort required to produce such material. 

Phosphorus standards can be produced by thoroughly mixing a sample with a known concentration of 

phosphorus (for example, NBS 120a, a phosphate rock 

standard) or a pure compound (Na3P04) with spectrographically pure graphite and then diluting this mixture 

in steps to give a series of samples that define the 

concentration range needed. These samples are then 

mixed with cellulose and briquetted as described previously. 

Likewise, chlorine standards are prepared by spiking graphite with a substance such as sodium chloride 

and then diluting the mixture with graphite in steps to 

produce a series of standards. Standards for other 

elements can be prepared in a similar fashion. 

Calibration for each element is accomplished by 

plotting concentration and intensity for all the available 

standards and calculating slope and intercept by a 

simple linear regression analysis. Results from a typical 

calibration for phosphorus are shown in table 15, where 

accepted and calculated concentrations are given. {The 

standards Syn-C through Syn-H were prepared synthetically, as described in the text. RM-120 through RM-124 

were analyzed by other methods. The value for NBS 

1632 is from Ondov and others (1975), and the value for 

NBS 1632a is from Germani and others (1980).) 

Although mathematical correction for absorption and 

enhancement by the other matrix elements may improve 

results (because minimal dilution is used), in practice, 

such corrections are difficult to accomplish because of 

the lack of well-characterized standards. Most matrix 

correction algorithms require that concentrations for all 

major and minor elements for the standards be known. 

Table 15. XRF calibration of P20 5 in whole coal: simple linear regression analysis results 

Standard 

Syn-C 

Syn-D 

Syn-E 

Syn-F 

Syn-G 

Syn-H 

RM-120 

RM-121 

RM-122 

RM-123 

RM-124 

NBS-1632 

NBS-1632a 

Concentration (P-g/g) 

Accepted Calculated 

2,610 

1,310 

653 

327 

163 

82 

300 

350 

600 

270 

160 

300 

500 

2,590 

1,310 

622 

321 

153 

77 

304 

354 

650 

200 

150 

280 

512 

38 Methods for Sampling and Inorganic Analysis of Coal 

Precision is determined by the sample preparation, instrument stability, and counting time and is 

generally in the 1- to 2-percent range. Because of the 

lack of appropriate standard reference materials and 

because of the uncertainty associated with those materials that are being used as reference standards in the 

calibrations, assessment of the accuracy of the chlorine 

and phosphorus determinations is difficult. In addition, 

there are no other methods for determining either of 

these two elements now in routine use at the U.S. 

Geological Survey to provide values for comparison. 

However, based on the few primary standards available, 

we estimate the relative precision of the method to be 

approximately 10 percent. 

CONCLUSIONS 

Methods based on XRF spectrometry are capable 

of determining 11 inorganic elements in coal, providing 

relative precision and accuracy of 2 to 5 percent for the 

determination of sulfur and major oxides in coal ash, 

and 10 percent for the determinations of chlorine and 

phosphorus in whole coal. The most important factor 

limiting the accuracy of analysis is the restricted availability of standard reference materials. Another significant factor that affects accuracy is that many coal 

samples not stored in a cool, dry, inert atmosphere 

decompose over time and, consequently, are subject to 

changes in composition. In addition, other elements, 

such as Mg, AI, Si, K, Ca, Ti, Mn, Fe, Cu, Ni, Zn, Rb, 

Sr, Y, Zr, Nb, and Ba have been determined in whole 

coal by methods quite similar to those previously 

described. 

REFERENCES 

Abbey, Sydney, 1983, Studies in "standard samples" of silicate 

rocks and minerals, 1969-1982: Geological Survey Canada Paper 83-15, 114 p. 

Germani, M.S., Gokmen, Inci, Sigleo, A.C., Kowalczyk, 

G.S., Olmez, Ilhan, Small, A.M., Anderson, D.L., Failey, 

M.P., Gulovali, M.C., Choquette, C.E., Lepel, E.A., 

Gordon, G.E., and Zoller, W.H., 1980, Concentration of 

elements in the National Bureau of Standards' bituminous 

and subbituminous coal standard reference materials: 

Analytical Chemistry, v. 52, no. 2, p. 240-245. 

Giauque, R.D., Garrett, R.B., and Goda, L.Y., 1979, Determination of trace elements in light element matrices by 

X-ray fluorescence spectrometry with incoherent scattered 

radiation as an internal standard: Analytical Chemistry, 

v. 51, no. 4, p. 511-519. 

Kuhn, J.K., Harfst, W.F., and Shimp, N.F., 1975, X-ray 

fluorescence analysis of whole coal, in Babu, S.P ., ed., 

Trace elements in fuel: Washington, D.C., American 

Chemical Society, p. 66-73. 

Mills, J.C., Turner, K.E., Roller, P.W., and Belcher, C.B., 

1981, Direct determination of trace elements in coal: 

X-Ray Spectrometry, v. 10, no. 3, p. 131-137. 
Norrish, K., and Hutton, J.T., 1969, An accurate X-ray 

spectrographic method for the analysis of a wide range of 

geological samples: Geochimica et Cosmochimica Acta, 

v. 33, no. 4, p. 431-453. 

Ondov, J.M., Zoller, W.H., Olmez, Ilhan, Aras, N.K., 

Gordon, G.E., Rancitelli, L.A., Abel, K.H., Filby, R.H., 

Shah, K.R., and Ragaini, R.C., 1975, Elemental concentrations in the National Bureau of Standards' environmental coal and fly ash reference materials: Analytical 

Chemistry, v. 47, no. 7, p. 1102-1109. 

Rose, H.J. Jr., Adler, Isidore, and Flanagan, F.J., 1963, 

X-ray fluorescence analysis of light elements in rocks and 

minerals: Applied Spectroscopy, v. 17, no. 4, p. 81-85. 

Taggart, J.E. Jr., and Wahlberg, J.S., 1980a, A new in-muffle 

automatic fluxer design for casting glass disks for X-ray 

fluorescence analysis: Conference of the Federation of 

Analytical Chemistry and Spectroscopy Societies, 7th, 

Philadelphia, paper 327a. 

-- 1980b, New mold design for casting fused samples, in 

Barrett, C.S., Leyden, D.E., Newkirk, J.B., Predecki, 

P.K., and Ruud, C.O., eds., Advances in X-ray analysis, 

v. 23: New York, Plenum Press, p. 257-261. 

Wheeler, B.D., 1983, Chemical analysis of coal by energydispersive X-ray fluorescence utilizing artificial standards, 

in Hubbard, C.R., Barrett, C.S., Predecki, P.K., and 

Leyden, D.E., eds., Advances in X-ray analysis, v. 26: 

New York, Plenum Press, p. 457-466. 

The Determination of Major and Minor Elements in Coal by X-ray Fluorescence Spectrometry 39 

ANALYSIS OF COAL ASH BY ATOMIC ABSORPTION 

SPECTROMETRIC AND SPECTROPHOTOMETRIC 

METHODS 

By Floyd W. Brown and Hezekiah Smith 

Abstract 

Methods for determining AI, Ca, Fe, Mg, Mn, P, K, Si, 

Na, and Ti in coal ash are described. A bead formed by fusing 

a mixture of sample and lithium metaborate-lithium tetraborate flux at 1,000 oc for 45 min is dissolved in dilute nitric acid. 

Measurements are made by atomic absorption spectrometry 

and by spectrophotometry on portions of the resulting solution. Selected silicate standards are used as control samr:>les to 

assure the quality of measurements. The precision of the 

methods commonly ranges from 1 to 10 percent relative 

standard deviation. The methods are both accurate and inexpensive and provide a good alternative to measurements by 

X-ray fluorescence spectrometry. 

INTRODUCTION 

The determination of major elements in coal ash 

requires the analysis of high-temperature ash residues 

having compositions that resemble those of silicate 

rocks. Thus, methods used in U.S. Geological Survey 

laboratories for routinely determining major elements 

(AI, Ca, Fe, K, Mg, Mn, Na, P, Si, and Ti} in silicate 

rocks (Shapiro, 1975) are, with certain modifications, 

applicable to coal-ash residues. The elements AI, P, Si, 

and Ti are determined spectrophotometrically, and the 

other six elements (Ca, Fe, K, Mg, Mn, and Na) are 

determined by flame atomic absorption spectrometry 

(AAS). The procedures were developed to facilitate the 

analysis of large numbers of samples. 

Each sample, which consists of 100 to 200 mg of 

coal ash ground to pass through a 100-mesh sieve, is 

mixed with a reagent-grade lithium metaborate-lithium tetraborate flux and fused at 1,000 oc for 45 min in 

a graphite crucible. Use of a mixed flux (1 part anhydrous lithium metaborate (LiB02) and 2 parts anhydrous lithium tetraborate (Li2B40 7)) prevents strong 

adhesion of the final bead to the wall of the graphite 

crucible. This feature is particularly important for samples having iron concentrations greater than 15 percent. 

Also, the use of the mixed flux produces more reliable 

values for silica than do fusions with only lithium 

tetra borate. 

In a practical procedure for determining major 

elements, the flux-to-sample ratio should be kept low to 

avoid the introduction of impurities, but the ratio must 

be high enough to assure complete decomposition of the 

sample. Concentrations of the major elements in solution must be sufficiently high to accommodate the least 

sensitive determinations but low enough to prevent silica 

from precipitating. These requirements are satisfied if 

0.2 g of sample is used with 1.2 g of flux. The same 

flux-to-sample ratio (6 to 1) is used with different sample 

sizes. The bead that results from the fusion of 0.2 g of 

sample is dissolved in dilute nitric acid and diluted to 

250 mL. Concentrations of major elements in this 

solution are determined by either spectrophotometry or 

by AAS. 

SPECTROPHOTOMETRIC PROCEDURES 

Silicon (as Si02) is determined spectrophotometrically by measuring the absorbance of a molybdenum complex at 640 nm (Bunting, 1944). In concentrations greater than 200 J.tg/mL, silica forms polyiJlers 

that do not react with the molybdate reagent. Formation 

of these polymers is prevented by the addition of 

fluoride, as sodium fluoride, to each solution. Because 

the fluoride solution dissolves glass, thus giving erratic 

results in determinations of silica, containers made of 

polyethylene, Teflon TM, or some similar material should 

be used. The interference caused by phosphate, which 

forms a phosphomolybdic acid complex, is avoided by 

adding tartaric acid to destroy the complex. 

Aluminum (as Al2 0 3) is determined spectrophotometrically by measuring the absorbance at 475 nm of the 

aluminum complex with calcium alizarin red-S (Parker 

and Goddard, 1950). Iron and titanium also form 

colored complexes that absorb at 475 nm, but these 

Analysis of Coal Ash by Atomic Absorption Spectrometric and Spectrophotometric Methods 41 
interferences are eliminated by the addition of potassium ferricyanide and thioglycolic acid as complexing 

agents. 

The titanium determination (as Ti02) is based on 

the use of disodium-1,2-dihydroxybenzene-3,5-disulfonate (Tiron) as a spectrophotometric reagent. The 

reagent forms a lemon-yellow titanium complex that has 

a high molar absorptivity (Yoe and Armstrong, 1947). 

The absorbance of this titanium complex is nearly 

independent of pH over the range 4.3 to 9.6. Ferric iron 

also reacts with Tiron to produce a purple complex, but 

this interference is eliminated by reducing the ferric iron 

with sodium dithionate solution buffered at pH 4. 7. The 

absorbance of the yellow titanium complex at 430 nm is 

measured spectrophotometrically. 

Phosphorus (as P 20 5) is determined spectrophotometrically by measurement of the absorbance of a 

heteropoly molybdenum-blue complex that forms upon 

reduction of heteropoly phosphomolybdic acid with 

stannous chloride solution. For the conditions used, 

only the molybdenuffi combined with phosphorus is 

reduced, and the excess molybdic acid is unaffected. 

ATOMIC ABSORPTION SPECTROMETRIC 

METHODS 

An aliquot of the original sample solution is 

diluted with lanthanum solution, and the absorption for 

Ca, Fe, K, Mg, Mn, or Na is measured by AAS. 

Operating conditions for the AAS instrument are presented in table 16. 

Table 16. Operating conditions for atomic absorption spectrometry 

Hollow Cathode Spectral 

Wavelength Lamp Current Bandpass 

Element (nm) (rnA) (nm) Flame Type 

Ca 422.673 10 to 25 0.7 Air-Acetylene 

Reducing 

Fe 248.327 30 0.2 Air-Acetylene 

Oxidizing 

(lean, blue) 

K 766.491 12 2.0 Air-Acetylene 

Oxidizing 

(lean, blue) 

Mg 285.213 6 to 15 0.7 Air-Acetylene 

Oxidizing 

(lean, blue) 

Mn 279.482 20 to 30 0.2 Air-Acetylene 

Oxidizing 

(lean, blue) 

Na 588.995 8 to 10 0.7 Air-Acetylene 

Oxidizing 

(lean, blue) 

42 Methods for Sampling and Inorganic Analysis of Coal 

PRECISION OF ANALYSIS 

The precision for major-element analyses, which is 

defined as the reproducibility of replicate determinations of a particular analyte, is described in table 17. 

The values of relative standard deviation in this table are 

estimates based on replicate determinations of major 

elements in both standards and samples. 

Table 17. Estimated precision of analysis 

Concentration 

(percent, w/w) 

>10 

1 to 10 

0.1 to 1 

<0.1 

Relative Standard Deviation 

(percent) 

1 to 2 

2 to 10 

10 to 50 

50 to 100 

PREPARATION OF SAMPLE SOLUTION 

Reagents and Supplies 

1. Flux mixture: 1 part reagent grade lithium metaborate (LiB02) and 2 parts anhydrous lithium tetraborate (Li2B40 7) are thoroughly mixed and stored in 

a closed container. Several hundred grams of the 

flux mixture should be prepared at one time. 

2. Standard control samples: Several U.S. Geological 

Survey silicate standards, such as W -2, BHV0-1, 

AGV-1, G-2, and RGM-1 and National Bureau of 

Standards (NBS) 1633a coal fly ash are analyzed 

along with the samples. Other established standards may be substituted. 

3. Graphite crucibles: Cylindrical, 25-mm outside diameter (20-mm inside diameter), high-purity 

graphite. 

4. Dilute nitric acid, 8 M: Prepare several liters. 

5. Polyethylene bottles: 250 mL, with caps. 

Procedure 

1. Weigh 0.2000 g of coal ash sample and mix thoroughly with 1.2 g of flux mixture on glassine 

paper. Transfer the sample-flux mixture into a 

graphite crucible. 

2. Weigh the standard control samples along with the 

other samples. Also, take through the procedure a 

crucible that contains only the flux mixture as a 

blank. 

3. Fuse the sample-flux mixtures in a muffle furnace at 

1,000 oc for 45 min. 
4. Remove the crucibles from the furnace and allow 

them to cool to room temperature. In most cases, 

the beads produced are easily dislodged from the 

crucibles by gentle tapping. If the iron content of 

a particular sample is exceptionally high, a spatula 

may be needed to remove the bead. 

5. Place each bead into a 250-mL polyethylene bottle, 

and add a Teflon TM-covered, 39-mm magnetic 

stirring bar. 

6. Add 50 mL of boiling distilled water to each bottle 

from a polyethylene graduated cylinder, and transfer the bottle to a magnetic stirrer. Then, add '5 

mL of 8 M nitric acid to each bottle. 

7. Stir each solution rapidly for approximately 60 min. 

Visually examine the bottle to be sure that dissolution of the bead is complete before going to the 

next step of the procedure. 

8. Remove the bottles from the stirrer, and add approximately 100 mL of distilled water to each. Catch 

the magnetic stirring bar in a funnel while pouring 

each solution into a separate 250-mL volumetric 

flask. Rinse the bottle, add water to the volumetric 

flask to mark, and mix. Pour the solution back 

into the polyethylene bottle for storage. 

DETERMINATION OF SILICON (AS Si02) 

Reagents and Equipment 

1. Ammonium molybdate solution: Dissolve 6.0 g of 

ammonium molybdate [(NH4) 6Mo70 24 · 4H20] in 

1 L of distilled water. 

2. Tartaric acid solution: Dissolve 16 g of tartaric acid 

[H2C2H4 0 6] in 1 L of distilled water. 

3. Reducing solution: Dissolve 0.28 g of sodium sulfite, 

3.6 g of sodium bisulfite, and 0.06 g of 1-amino2-naphthol-4-sulfonic acid in 1 L of distilled water. 

Prepare this solution within 48 h of use. 

4. Dilute sodium fluoride solution: Dilute 20 mL of a 

3-percent sodium fluoride solution and 5 mL of 9 

M sulfuric acid to 1 L with distilled water. 

5. Ultraviolet-visible spectrophotometer, with 1-cm cell. 

Procedure 

1. Transfer 0.500-mL aliquots of solutions of the blank, 

the standards, and the samples into a series of 

100-mL polyethylene beakers. Use a highprecision, 0.500-mL piston-type pipet to make 

these transfers. If the silica concentration is 

expected to be low, larger aliquots of sample 

solutions should be used. The following reagents 

then are added by a pipeting machine. 

2. Add 25 mL of the dilute sodium fluoride solution to 

each beaker and let the mixture sit for 5 min. 

3. Add 25 mL of the molybdate solution to each beaker, 

and let the mixture sit for 10 min. · 

4. Add 25 mL of the tartaric acid solution to each 

beaker. 

5. Add 25 mL of the reducing solution to each beaker, 

and let the mixture sit for at least 45 min. The 

color of the complex is stable for at least 6 h. 

6. Set the concentration scale of the spectrophotometer 

to zero for a wavelength of 640 nm with the blank 

solution in the absorption cell. Then, set the 

concentration scale with a solution having a known 

concentration of silica (standard silicate reference 

material), and determine directly the percent silica 

in each of the samples. 

DETERMINATION OF ALUMINUM (AS Al 20 3) 

Reagents, Supplies, and Equipment 

1. Complexing solution: To 880 mL of distilled water 

add 0.3 g of potassium ferricyanide [K3Fe(CN)6], 

40 mL of 10 percent hydroxylamine hydrochloride 

[NH20H · HCl] solution, and 80 mL of calcium 

chloride solution. The calcium chloride solution is 

prepared by dissolving 14 g of calcium carbonate 

(CaC03) in 30 mL of concentrated hydrochloric 

acid and diluting to 1 L. The complexing solution 

should be prepared on the same day that it is to be 

used. 

2. Thioglycolic acid solution: Dilute 3 mL of the pure 

acid to 1 L with distilled water. 

3. Buffer solution: Dissolve 80 g of sodium acetate 

[NaC2H30 2 · 3H20] in 975 mL of distilled water 

and add 24 mL of glacial acetic acid. 

4. Alizarin red-S stock solution, 0.10 percent: Dissolve 

1.0 g of the pure dye in 1 L of distilled water and 

filter the resulting solution. 

5. Alizarin red-S, 0.02 percent: Dilute 200 mL of the 

stock solution to 1 L with distilled water. 

6. Ultraviolet-visible spectrophotometer, with 1-cm cell. 

Procedure 

1. Transfer 0. 750 mL of the blank, standard solution, 

and each of the sample solutions into a series of 

150-mL beakers using a high-precision piston 

pipet. Add the following reagents to each beaker 

by pipeting machine. 

2. Add 25 mL of the complexing solution. 

3. Add 25 mL of the thioglycolic acid solution, and let 

the mixture sit for 5 min. 

Analysis of Coal Ash by Atomic Absorption Spectrometric and Spectrophotometric Methods 43 
4. Add 25 mL of the buffer solution, and let the mixture 

sit for 10 min. 

5. Add 25 mL of the 0.02-percent alizarin red-S solution, and let the mixture sit for 45 to 75 min. 

6. Set the concentration scale of the spectrophotometer 

to zero for a wavelength of 475 nm with the blank 

solution in the absorption cell. Then, set the 

concentration scale with a solution having a known 

concentration of alumina (standard silicate reference material), and determine directly the percent 

alumina in each of the samples. 

DETERMINATION OF PHOSPHORUS (ASPL05 ) 

Reagents and Equipment 

1. Ammonium molybdate stock solution: Dissolve 

12.5 g of ammonium molybdate 

[(NH4) 6Mo70 24 • 4H20] in 340 mL of distilled 

water. Then, add 160 mL of 9 M sulfuric acid. 

2. Dilute ammonium molybdate solution: Dilute 20 mL 

of stock ammonium molybdate solution to 1 L. 

3. Stannous chloride solution: Dissolve 0.600 g of stannous chloride [SnC12 • 2H20] in 25 mL of concentrated hydrochloric acid and dilute to 1 L with 

distilled water. This solution should be freshly 

prepared just prior to use. 

4. Ultraviolet-visible spectrophotometer, with 1-cm cell. 

Procedure 

1. Transfer 10-mL aliquots of the blank, standards, and 

the sample solution to a series of 100-mL polyethylene beakers. 

2. Add 25 mL of the dilute molybdate solution, and let 

the mixture sit for 10 min. 

3. Add 25 mL of the stannous chloride solution. The 

developed color is stable for approximately 40 

min. 

4. Set the concentration scale of the spectrophotometer 

to zero for a wavelength of 640 nm with the blank 

solution in the absorption cell. Then, set the 

concentration scale with a solution having a known 

concentration of phosphorus pentoxide (standard 

silicate reference material), and determine directly 

the percent phosphorus pentoxide in each of the 

samples. 

DETERMINATION OF TITANIUM (AS Ti02) 

Reagents and Equipment 

1. Disodium-1 ,2-dihydroxybenzene-3,5-disulfonate 

(Tiron): Dry reagent powder. 

44 Methods for Sampling and Inorganic Analysis of Coal 

2. Buffer solution: Dissolve 80 g of ammonium acetate 

[NH4C2H30 2] and 30 mL of glacial acetic acid in 

2 L of distilled water. 

3. Sodium dithionate [Na2S20 4] (sometimes sold as 

sodium hydrosulfite): Dry reagent powder. 

Procedure 

1. Transfer 10-mL aliquots of the blank, each of the 

standards, and each of the sample solutions to a 

series of 150-mL beakers. 

2. Add 125 mg of Tiron reagent powder to each beaker. 

3. Add, by pipeting machine, 25 mL of the buffer 

solution to each beaker. Then, add 50 mL of 

distilled water to each beaker. 

4. Add 10 to 20 mg of sodium dithionate to the blank 

and mix gently. Avoid vigorous mixing, which 

causes sulfur to precipitate. Then, set the concentration scale of the spectrophotometer to zero for 

a wavelength of 430 nm with the blank solution in 

the absorption cell. 

5. Add sodium dithionate to one of the standard solutions and set the concentration scale of the spectrophotometer to the known concentration value 

(standard silicate reference material). Determine 

directly the percent Ti02 in each of the samples. 

Sodium dithionate may be added to six solutions 

at a time. 

DETERMINATION OF CALCIUM, IRON, 

MAGNESIUM, MANGANESE, POTASSIUM, AND 

SODIUM 

Reagents and Equipment 

1. Lanthanum solution: Transfer 140 g of lanthanum 

oxide (La20 3 , 99.997 percent pure) into a 2-L 

beaker. Slowly add 300 mL of concentrated hydrochloric acid, allowing time for the reaction to be 

completed after each addition of acid. Then, add 

200 mL of distilled water. Each 4 mL of the final 

solution contains approximately 1 g of lanthanum. 

2. Manganese stock solution: Transfer 0.3872 g of pure 

manganese metal into a glass beaker, add 20 mL 

of hot 8 M nitric acid, and gently boil the nitric 

acid for several minutes. After the resulting solution has cooled to room temperature, transfer the 

solution to a 500-mL volumetric flask and dilute to 

volume with distilled water. The concentration of 

MnO in this solution is 1 ,000 t-tglmL. 

3. Stock multiple-element standard solution: Transfer 

0.8924 g of CaC03 , 0.9435 g of NaCl, 0.7915 g of 

KCI, and 2.4556 of FeSOiNH4hS04 • 6H20, [all 
reagent-grade purity] and 0.3045 g of magnesium 

ribbon to a 500-mL volumetric flask. (Magnesium 

ribbon generally is 99 percent magnesium; therefore, the weight of the ribbon includes a 1-percent 

correction.) Add 50 mL of distilled water and 10 

mL of concentrated hydrochloric acid. Boil the 

dilute acid to dissolve all the constituents. After 

the solution cools to room temperature, add 50.0 

mL of the manganese stock solution (1 ,000 J.tg/mL 

of MnO), dilute to volume with distilled water, 

and thoroughly mix the final solution. This solution contains the equivalent of 1.00 mg/mL each 

of Fe20 3 , CaO, MgO, Na20, and K20, and 0.1 

mg/mL of MnO. 

4. Working standard solutions: To six 250-mL volumetric flasks, add 0, 6, 12, 18, 24, and 30 mL of the 

standard stock solution. Then, add 1.2 g of flux 

mixture, 5 mL of 8 M nitric acid, and approximately 200 mL of distilled water. Agitate the nitric 

acid solution to dissolve the flux mixture. Then, 

add distilled water to make the final volume 250 

mL and make the solution homogeneous by vigorous mixing. These six solutions represent a 

blank and 3-, 6-, 9-, 12-, and 15-percent (equivalent in the sample) standard solutions. For MnO, 

the same six solutions represent a blank and 0.3-, 

0.6-, 0.9-, 1.2-, and 1.5-percent standard solutions. 

Procedure for Calcium, Iron, Magnesium, 

and Manganese 

1. Transfer 0. 750 mL of blank, sample, and standard 

solutions into small vials or beakers. 

2. Dilute 8 mL of lanthanum solution with 200 mL of 

distilled water. Add 6.5 mL of this solution to all 

standards, samples, and blanks. 

3. Calibrate the atomic absorption spectrometer by setting the concentration scale to zero for the recommended wavelength (table 16) while the blank 

solution is nebulized into the flame. Then, set the 

concentration scale with the 6-percent working 

standard, and verify this setting with solutions of 

silicate standards. Directly measure the concentrations of calcium, iron, magnesium, and manganese in each of the samples. Most available atomic 

absorption spectrometers are suitable for these 

measurements; the optimum operating conditions 

for each element usually are discussed in the 

manual provided with the spectrometer. Importantly, the individual measurements of concentration (or, absorbance) for a sample should be 

"bracketed" between those of standards because 

the instrumental responses are usually not linear. 

Procedure for Potassium and Sodium 

1. Transfer 0.200 mL of blank, sample solutions, working standards, and silicate standards into a small 

vial or beaker. 

2. Dilute 1.2 mL of lanthanum solution with 200 mL of 

distilled water. Add 5.0 mL of this solution to the 

blank and to each of the standards and samples. 

3. Calibrate the atomic absorption spectrometer using 

the concentration mode with the 6-percent working standard, and check appropriate silicate standards for known values. Measure directly the 

concentration of samples. 

CONCLUSIONS 

Methods based on AAS and spectrophotometry 

provide accurate determinations of 10 inorganic elements in coal ash. Although not as rapid as X-ray 

fluorescence (XRF) spectrometry, these methods furnish 

an approach to determining major oxides in coal ash 

that is both inexpensive and accurate (table 18). The 

agreement between our measurements and the NBScertified concentrations for 10 elements in NBS 1633a 

coal fly ash, demonstrated by data in table 18, is quite 

acceptable. Results from XRF spectrometry for Si02 , 

Al20 3 , and Fe20 3 in ash sample number 1 and for Si02 

in sample number 7 (table 18) are outside the range 

covered by the standards used for calibration. Thus, 

extrapolations beyond this range could introduce error 

into these determinations. 

REFERENCES 

Bunting, W.E., 1944, The determination of soluble silica in 

very low concentrations: Industrial and Engineering 

Chemistry (analytical ed.), v. 16, p. 612-615. 

Parker, C.A., and Goddard, A.P., 1950, The reaction of 

aluminum ions with alizarin-3-sulfonate, with particular 

reference to the effect of calcium ions: Analytica Chimica 

Acta, v. 4, no. 5, p. 517-536. 

Shapiro, L., 1975, Rapid analysis of silicate, carbonate, and 

phosphate rocks: U.S. Geological Survey Bulletin 1401, 

revised ed., 76 p. 

Yoe, J.H., and Armstrong, A.R., 1947, Colorimetric determination of titanium with disodium-1 ,2-dihydroxybenzene3,5-disulfonate: Analytical Chemistry, v. 19, p. 100-102. 

Analysis of Coal Ash by Atomic Absorption Spectrometric and Spectrophotometric Methods 45 
ol:> 

0'1 

~ I'D 

:r 

0 

c. 

Ill 

~ Ill 

I» 

3 

"'2.. 

:;· 

CJCI 

I» 

::;, 

c. 

::;, 

0 

al 

I» 

::;, 

r:;· 

> ::;, 

I» 

-< Ill 

iii" 

s. 

n 

0 

e!.. 

Table 18. Compositions of coal ashes determined by methods based on atomic absorption spectrometry (AAS) or spectrophotometry (Sa) and on X-ray fluorescence 

(XRF) spectrometryb 

Sample Si02 Al203 Fe203 d MgO 

AAS,S XRF AAS,S XRF AAS,S XRF AAS,S XRF 

NBS 1633A 48.6 48.8 27.1 27.0 13.5 13.4 0.78 0.75 

Ash 1 6.2 9.9 4.0 4.1 67.4 60.3 0.28 ND 

Ash 2 37.5 38.1 24.2 25.2 12.3 11.9 0.52 ND 

Ash 3 53.4 54.5 22.3 23.8 13.4 15.3 1.0 ND 

Ash 4 26.2 26.3 12.0 10.9 47.6 45.5 0.59 ND 

Ash 5 56.9 57.6 24.5 25.3 7.3 7.5 1.2 ND 

Ash 6 51.5 47.6 30.3 30.4 6.2 6.1 0.96 ND 

Ash 7 15.1 18.9 22.0 21.2 26.6 28.2 1.2 ND 

Ash 8 48.6 47.5 26.9 29.8 15.8 16.9 0.40 ND 

Ash 9 45.4 48.5 15.4 18.7 4.7 4.4 2.2 ND 

a Only Al203 , P20 5 , Si02 , and Ti02 were determined by spectrophotometric methods. 

b Analyst: George Sellers. 

c ND: not determined. 

d Total Fe is reported as Fe203 • 

Concentration (percentc) 

CaO Na20 K20 Ti02 P20s Mno 

AAS,S XRF AAS,S XRF AAS,S XRF AAS,S XRF AAS,S XRF AAS,S XRF 

1.6 1.6 0.19 0.23 2.2 2.3 1.4 1.3 0.42 ND 0.05 0.02 

9.0 9.4 0.26 ND 0.30 0.26 0.18 0.13 0.02 0.05 0.08 0.09 

9.5 9.5 0.75 ND 1.2 1.2 1.0 0.97 0.21 0.18 0.06 0.06 

0.44 0.40 0.49 ND 2.9 2.8 1.0 1.2 0.16 0.09 0.03 0.03 

3.4 3.6 0.38 ND 1.2 1.2 0.59 0.64 0.15 0.12 0.06 0.07 

0.67 0.57 0.43 ND 3.3 3.3 1.2 1.3 0.39 0.30 0.02 0.02 

0.40 0.40 0.25 ND 4.1 4.0 1.2 1.1 0.12 0.15 0.01 0.05 

9.3 10.2 0.43 ND 0.10 0.13 0.88 0.87 2.4 2.8 0.02 0.03 

1.8 1.7 0.15 ND 0.57 0.62 0.94 0.94 0.17 0.12 0.01 0.03 

16.6 17.3 0.12 ND 1.1 1.1 1.4 1.3 0.15 0.25 0.10 0.11 
THE DETERMINATION OF SELECTED ELEMENTS IN 

COAL ASH BY ATOMIC ABSORPTION 

SPECTROMETRY 

By Jean S. Kane 

Abstract 

Methods for the determination of eight elements in coal 

ash by atomic absorption spectrometry are described. Results 

from analyses of two National Bureau of Standards (NBS) 

standard reference materials, coal fly ashes NBS 1633 and 

1633a, and four quality-control samples are reported. Possible 

sources of error in each method are discussed, and steps in the 

procedure critical to accuracy and precision are identified. 

Accuracy of the methods is established by comparisons of 

measured concentrations for elements in NBS standards 1633 

and 1633a with certified values and with other values reported 

in the literature. 

INTRODUCTION 

The elements Cd, Cu, Li, Mg, Mn, Na, Pb, and 

Zn are determined in coal ash by methods based on 

atomic absorption spectrometry (AAS). These methods 

are described, and results are reported from the analyses 

of two National Bureau of Standards (NBS) standard 

reference materials, coal ashes NBS 1633 and 1633a, 

and four U.S. Geological Survey in-house, qualitycontrol samples. Comparisons of elemental concentrations determined for NBS 1633 and NBS 1633a to 

certified concentrations and to other values reported in 

the literature establish the accuracy of the methods. 

EXPERIMENTAL METHODS AND PROCEDURES 

Dissolution of Samples 

A coal-ash sample, 500 ±1 mg, is weighed into a 

50-mL Teflon TM beaker to which 10 mL of hydrochloric 

acid, 3 mL of perchloric acid, and 10 mL of hydrofluoric 

acid are added. Each of these acids is concentrated and 

of reagent-grade quality. The mixture of acids and 

sample is heated in an uncovered beaker for 1 h on a hot 

plate having a surface temperature of 200 °C. Then, the 

beaker is removed from the hot plate and allowed to cool 

for 5 min, and 2 mL of nitric acid is added. The beaker 

is returned to the hot plate and heated until dense fumes 

of perchloric acid are formed and the acid volume has 

been reduced to :53 mL. The beaker is again removed 

from the hot plate and allowed to cool for 5 min, and 2 

mL of nitric acid plus 5 mL of hydrochloric acid are 

added. The beaker is returned to the hot plate, and the 

mixture within is evaporated overnight to complete 

dryness. Finally, the beaker and its contents are cooled 

for 5 min, 2.5 mL hydrochloric acid is added, and the 

wall of the beaker is washed with approximately 5 mL of 

distilled water to dissolve the residue. Gentle warming of 

this solution for 5 to 10 min completes the dissolution 

and produces a clear solution that is transferred to a 

50-mL linear polyethylene volumetric flask. This flask is 

filled to the volume mark with water after the solution 

reaches room temperature. For this approach, the concentration of an element in a sample of coal ash equals 

the concentration of the element in the sample solution 

times 100. 

Determinations of Cu, Li, Pb, Mn, and Zn are 

made directly on each final solution. However, determinations of Na and Mg are made only after diluting each 

solution 1 to 100 with a matrix-modifier solution ~ontaining lanthanum at a concentration of 1,000 J.tg/mL. 

The cadmium determination requires extraction of the 

element with dithizone into xylene. 

Cadmium Extraction 

Typically, 12 samples, 2 blanks, and 4 calibration 

standards are extracted as a set. The concentrations of 

the calibration standards should range from 1 to 15 

ng/mL in solutions freshly prepared by diluting a stock 

solution that contains 100 J.tg/mL of cadmium. 

The Determination of Selected Elements in Coal Ash by Atomic Absorption Spectrometry 47 
Pipet 5 mL of the sample solution, blank, or 

calibration solution, described later, into a 60-mL 

separatory funnel. Add 0.50 mL of 20 percent (w/v) 

hydroxylamine hydrochloride, 5 mL of 10 percent (w/v) 

sodium potassium tartrate, and 5 mL of 10 percent 

(w/v) sodium hydroxide. Then, add 15 mL 0.10 percent 

(w/v) dithizone in xylene, and mix for 5 min by an air 

bubbler or by a mechanical shaker. Allow the layers to 

separate, and discard the aqueous layer. 

The xylene (upper) layer varies in color from pale 

straw to pink to a deep, almost-black purple, depending 

on the amounts of Zn, Pb, and Mn that coextract with 

the Cd. The coextracted elements are not extracted from 

the xylene layer in subsequent steps. The aqueous layer 

should be distinctively orange. 

After discarding the aqueous layer, wash the xylene phase twice with 5 mL of 0.10 percent (w /v) 

ammonium hydroxide, agitate the mixture for 1 min, 

and discard the aqueous wash solution each time. 

Back extract the cadmium into 5 percent (v /v) 

hydrochloric acid by adding 10 mL of 5 percent hydrochloric acid to the xylene phase in each funnel, and then 

mix each solution for 10 min with either an air bubbler 

or a mechanical shaker. Rinse the stem of each 

separatory funnel with distilled water, and dry each stem 

with a Kim wipe TM. Then, collect the aqueous phase, 

which is needed for the AAS measurement. The concentration of cadmium in the coal-ash sample is equal to the 

concentration of cadmium measured in the stripped 

solution times 200. 

Calibration Solutions 

Solutions for calibration of the atomic absorption 

spectrometer are prepared to contain Cu, Li, Mn, and 

Zn in 5 percent (v /v) hydrochloric acid at concentrations ranging from 0.10 to 20 11g/mL by serial dilutions 

of single-element stock solutions in which each element 

has a concentration of 1,000 11g/mL. Four to five 

solutions are prepared to calibrate over each decade of 

concentration. 

Solutions of lead, which have the same range of 

concentrations as the previous multiple-element solutions, are matched to the matrix of a typical coal ash by 

adding an aliquot of a concentrated iron solution to give 

a final iron concentration of 5,000 11g!mL. The use of 

solutions that contain the principal elements aluminum, 

calcium, and iron provide no improvement in matrix 

matching over the iron solution alone. 

Concentrations of magnesium and sodium in calibration solutions range from 0.05 to 2.0 11g!mL. These 

calibration solutions contain 0.10 percent lanthanum to 

minimize errors originating from matrix suppression of 

the magnesium absorption and from ionization effects 

on sodium. 

48 Methods for Sampling and Inorganic Analysisof Coal 

Calibration solutions for cadmium are taken 

through the extraction procedure previously described. 

Without this extraction, background correction by use 

of a deuterium lamp is inadequate in the determination 

of cadmium. 

INSTRUMENTATION 

All measurements by flame AAS are made by 

either a Perkin-ElmerR model603 or model5000 atomic 

absorption spectrometer that has background correction 

based on a deuterium arc lamp. Measurements of 

cadmium by electrothermal-atomization AAS are 

accomplished with a Perkin-ElmerR model 603 atomic 

absorption spectrometer that has deuterium-lamp background correction, a graphite atomizer (model 500 or 

model 2100), a model AS40 autosampler, and a model 

56 strip chart recorder. Solution volumes of 20 11L are 

injected into nonpyrolytic graphite tubes that are purged 

by argon. Each hollow cathode lamp used in these 

measurements is operated at the current recommended 

by the manufacturer. 

Instrumental operating parameters for each of the 

elements determined are listed in table 19. Although the 

Table 19. Operating parameters: flame and graphitefurnace atomization 

Wavelength Bandpass Background 

Element (nm) (nm) Correction Cell a Matrix 

Cd 228.8 0.7 Yes Graphite 0.5o/o ash 

Furnace solution; 

extract in 

5% HCl 

Cu 324.7 0.7 No Flame 1% ash 

solution in 

5% HCl 

Li 670.8 1.4 No Flame 1% ash 

solution in 

5% HCl 

Mg 285.2 0.7 No Flame 0.01% ash 

solution in 

5% HCl 

Mn 279.5 0.2 No Flame 1% ash 

solution in 

5% HCl 

Na 589.0 0.2 No Flame 0.1% ash 

solution in 

5% HCl 

Pb 217.0 0.7 Yes Flame 0.1% ash 

solution in 

5% HCl 

Zn 213.9 0.7 Yes Flame 1% ash 

solution in 

5% HCl 

a Flame: Fuel-lean air-acetylene. 

Graphite furnace: 20-JA.L sample, argon sheath gas, conventional graphite tube. Furnace sequence: (1) Dry for 20 sat 110 oc. (2) 

Char for 25 sat 250 °C. (3) Atomize for 5 sat 2,100 oc with 1 s ramp 

to temperature. Interrupt gas flow (default to 50 mL/min with the 

model 2100 HGA.) 
Table 20. Detection limits, sensitivities, and calibration ranges for flame and graphite-furnace atomic absorption spectrometry 

Wavelength 

Element (nm) 

Cda 228.8 

Cub 324.7 

Lib 670.8 

Mgb 285.2 

Mnb 279.5 

Nab 589.0 

Pbb 217.0 

znb 213.9 

a Graphite-furnace AAS (ng/mL). 

b Flame AAS (t-tg/mL). 

c For 0.0044 absorbance. 

Detection Limit 

0.05 

0.02 

0.02 

0.04 

0.08 

0.01 

operation ofa fuel-lean (blue) flame and the use of an 

observation height of five units on the vernier of the 

burner head are common to all measurements reported 

here, the accuracy of these measurements is relatively 

insensitive to variations in flame stoichiometry and 

observation height. Thus, an inability to reset exactly 

these parameters on a day-to-day basis should be of no 

consequence. 

Detection limits, sensitivities, and approximate 

upper limits of linearity for calibration curves are listed 

in table 20. Detection limits for the cited elements are a 

simple function of dilution and thus can be improved by 

as much as a factor of 5 by decreasing the extent to 

which the dissolved sample is diluted. For cadmium, a 

change in the extraction factor can improve the detection limit by up to a factor of 10. For most coal ashes, 

the sensitivities for individual elements need to be 

reduced much more frequently than the detection limits 

need to be improved. Such a reduction in sensitivity can 

be accomplished either through serial dilutions of the 

sample solution until the analyte concentration is within 

the linear calibration range or through a reduction of 

the effective length of the flame that is accomplished by 

rotation of the burner head. Only positions at 30°, 60°, 

Concentrationa,b in Solution for 

Upper Limit of Usable Nonlinear 

Sensitivityc Linear Calibration Range 

0.065 5.0 5 -20 

0.07 5.0 5 - 15 

0.035 2.0 2 - 10 

0.008 0.5 0.5 - 2 

0.07 3.0 3 -10 

0.02 1.0 1 - 5 

0.2 5.0 5 - 25 

0.02 2.0 2 -10 

and 90° can be reproducibly set on the Perkin-ElmerR 

model 603 spectrometer, but the model 5000 permits the 

continuous variation of the burner position through 

90°. For copper, manganese, and lead, the option of 

using less-sensitive spectral lines for measurements is 

available. Alternate operating parameters that can produce reduced sensitivity are listed along with detection 

limits, sensitivities, and calibration ranges in table 21. 

Also, alternative approaches are available through standard methods described in American Society for Testing 

and Materials (1984a, b) publications. 

DISCUSSION OF RESULTS 

The accuracy of analysis for the AAS methods 

described here is verified by comparisons of measurements on NBS standard reference materials 1633 (table 

22) and 1633a (table 23) with certified concentrations 

and with concentrations determined by instrumental 

neutron activation analysis (Ondov and others, 1975; 

Rowe and Steinnes, 1977). U.S. Geological Survey "inhouse" standards, designated ASH1, S1, S2, and S3 in 

table 23, are used as references to provide long-term 

accuracy and to conserve supplies of NBS standard 

Table 21. Alternate operating parameters for flame atomic absorption spectrometry and calibration ranges 

Burner Head Calibration Range 

Wavelength Bandpass Background Position, (~.~-glmL in solution) 

Element (nm) (nm) Correction Oxidant Fuel Linear Nonlinear 

Cu 324.7 0.7 No Rotated 60°, 5- 300 300- 700 

Air-acetylene 

Mg 285.2 0.7 No Rotated 60°, 2- 10 

Air-acetylene 

Mn 280.1 0.2 No Rotated 60°, 5- 50 50- 200 

Air-acetylene 

Zn 213.9 0.7 Yes Rotated 60°, 1 - 20 

Air-acetylene 

Rotated 90°, 5 - 50 

Nitrous oxideacetylene 

The Determination of Selected Elements in Coal Ash by Atomic Absorption Spectrometry 49 
Table 22. Concentrations of eight elements in the NBS 1633 coal fly ash determined by atomic absorption spectrometric 

methods 

Concentration (f.tg/g) 

EPA-NBS 

This Work Certificate of Round Robinb 

Element (n)a analysis (Range) Literaure Reference 

Cd 1.56 ± 0.26(17) 1.45 ± 0.06 0.88- 6.0 1.5 ± 0.2 Gladney (1980) 

Cu 130 ± 6(16) 128 ± 5 127 ± 8 Gladney (1980) 

115±8 Rowe and Steinnes (1977) 

Li 170 ± 13(17) 110±? Gladney (1980) 

Mg 1.17 ± 0.049(14) 1.6 ± 0.3 Gladney (1980) 

1.78 ± 0.20 Rowe and Steinnes ( 1977) 

Mn 496 ± 34(17) 493 ± 7 181 - 636 492 ± 24 Gladney (1980) 

509 ± 20 Ondov and others (1975) 

488 ± 14 Rowe and Steinnes ( 1977) 

Na 0.295 ± 0.023(11) 0.320 ± 0.034 Gladney ( 1980) 

0.283 ± 0.014 Rowe and Steinnes ( 1977) 

Pb 67 ± 4(10) 70 ± 4 18.7 - 110 72 ± 5 Gladney ( 1980) 

Zn 210 ± 10(18) 210 ± 20 54.2- 244 213 ± 13 Gladney (1980) 

a The number of replicate determinations = n. 

b Laboratory averagts from round-robin analyses by AAS 

(EPA, 1977). 

EPA: U.S. Environmental Protection Agency. 

NBS: National Bureau of Standards. 

reference materials. The precision of each method is 

expressed as the standard deviation for 10 or more 

replicate determinations. Factors that are important to 

the maintenance of accuracy and precision are treated in 

the following discussions on individual elements. 

Manganese 

In general, determinations of manganese are 

biased low for measurements on Mn 279.42 nm if 

spectral background corrections are based on the use of 

a deuterium arc lamp. Iron lines at 279.42, 279.47, and 

216 ± 25 Ondov and others ( 197 5) 

201 ± 6 Rowe and Steinnes (1977) 

279.50 nm, which occur within the spectrometer bandpass for the Mn 279.42-nm line, absorb the continuum 

radiation from the deuterium lamp and thus produce an 

overcorrection for background (Zander, 1976). Because 

of the close proximity of the iron lines to Mn 279.42 nm, 

reduction of the spectrometer slit width produces no 

improvement. Also, at minimal slit widths, analyte 

absorption of the continuum radiation produces overcorrection for background. Furthermore, matrix matching cannot be used to eliminate this error because of the 

variability of concentrations of iron in coal ashes. For 

best accuracy, a background correction should not be 

made for manganese. 

Table 23. Concentrations of analytes determined for NBS standard reference material1633a and for quality-control samples 

(p,g/g)a 

NBS 1633a 

Analyte This Work Certificate ASH1 

Cd 0.98 ± 0.08 1.0±0.15 0.71 ± 0.13 

Cu 114±7 118±3 141 ± 7 

Li 184 ± 14 153 ± 10 

Mg(o/o) 0.436 ± 0.005 0.455 ± 0.01 0.51 ± 0.03 

Mn 160 ± 12 190b 160 ± 11 

190c 

Na(%) 0.158 ± 0.014 0.170 ± 0.01 0.18 ± 0.03 

Pb 62 ± 4 72.4 ± 0.4 185 ± 17 

Zn 211 ± 11 220 ± 10 147 ± 8 

a Concentration units for Mg and Na are percent, or cg/g. 

b Concentration listed "for information only" by NBS, that is, 

the value is not certified. 

c From Gladney ( 1980). 

50 Methods for Sampling and Inorganic Analysis of Coal 

51 52 53 

1.4 ± 0.2 0.52 ± 0.09 0.49 ± 0.1 

65 ± 4 81 ± 3 127 ± 4 

96 ± 13 273 ± 9 200 ± 23 

0.65 ± 0.04 0.46 ± 0.02 0.58 ± 0.04 

251 ± 10 124 ± 9 222 ± 22 

0.44 ± 0.04 0.13 ± 0.02 0.22 ± 0.02 

60 ± 8 44 ± 13 53± 7 

66 ± 13 89 ± 4 106±6 
G 0.50 ppm Pb 

0.800 & 1.00 ppm Pb 

G 3.00 ppm Pb 

0.700 

0 

C\J 

X 

L.U 

0 

z 

<( 

co 

<( 

co 

CJ) 

a: 

0 

0.200 

~ 

2000 4000 6000 8000 10,000 

ppm IRON IN SOLUTION 

EQUIVALENT TO 2.0 4.0 6.0 8.0 100% 

IRON IN SAMPLE 

Figure 12. Lead absorbance as a function of 

iron concentration in the sample matrix. 

Lead 

As the concentration of iron increases from 0 to 

1,000 p,g/mL, the lead atomic absorption signal is 

sharply suppressed. Further increments in iron concentration up to 4,000 to 5,000 p,g/mL produce little further 

suppression of lead absorption, as illustrated in figure 

12. Typically, matrix matching can be used to correct 

for this suppression over most of the concentration 

range encountered in the analysis of coal ash. Lead 

calibration solutions, each containing iron at a concentration of 1,000 p,g/mL, are well suited for this purpose. 

However, this approach overcorrects when iron occurs 

at concentrations below 5 percent in the ash and is 

inadequate for iron concentrations above 40 to 50 

percent in the ash. In the latter case, removal of the iron 

from solution by extraction with concentrated hydrochloric acid into methylisobutylketone is necessary 

before measuring lead absorbance. The method of standard additions is unsatisfactory in correcting for the 

suppression of lead absorption signal because of the 

greatly reduced sensitivity for lead absorption measurements. Furthermore, the extraction of lead by diethylammonium diethyldithiocarbamate prior to measurement 

is unsuccessful because of the coextraction of iron by 

this reagent. 

Although most AAS methods use the Pb 283.3-nm 

line, the more sensitive 217 .0-nm line is recommended 

for detectability that is better by a factor of 2.5. 

Background correction at this wavelength is essential. 

The Sb 217 .59-nm line potentially can cause overcorrection for background (Vajda, 1981), but Pb-to-Sb concentration ratios in coal ash are so high that this error is 

rarely significant. 

Zinc 

The concentrations of zinc in NBS 1633 determined by AAS are in excellent agreement with the NBS 

certificate value. Background correction is required at 

the Zn 213.86-nm line. Positive bias can occur for zinc 

determinations in coal ashes having high iron concentrations because of the direct spectral overlap of iron 

213.859 nm on zinc 213.856 nm. For a concentration of 

10 percent iron in the ash, the error is equivalent to 15 

ppm of zinc. For typical coal ashes, which have zinc 

concentrations between 200 and 1300 ppm, the relative 

error is less than 5 percent. Precision of measurements, 

which generally is ±5 percent, is illustrated by the plot in 

figure 13 of zinc concentrations measured for duplicate 

dissoluti.ons of various samples. Data for the other seven 

elements are quite similar and thus are not shown here. 

Copper 

Measurements of copper in NBS 1633 by AAS 

show the best accuracy and precision of the eight 

elements determined. Background corrections are not 

needed. 

Lithium 

Prior to 1980, values for lithium concentrations in 

coal-ash standards were unavailable in the literature. 

Thus, accuracy of analysis was evaluated from concurrent measurements of lithium concentrations in several 

U.S. Geological Survey standard rocks. The dissimilarities of both matrices and concentration ranges for 

lithium cause problems in comparisons. For example, 

the lithium concentrations determined for standard 

rocks generally have relative standard deviations of 5 

percent, which is only half that observed for coal ashes. 

The Determination of Selected Elements in Coal Ash by Atomic Absorption Spectrometry 51 
E 

Q. 

Q. 

z 

0 

i= 

<( 

a: 

1-

z 

UJ 

() 

z 

0 

() 

() 

z 

N 

1 00 200 300 400 500 700 

ZINC CONCENTRATION (ppm) 

Figure 13. Zinc correlation plot. 

Solutions of coal ash naturally contain concentrations of total alkalis (Na + K) that approach 2,000 

J.tg/mL. Thus, additional ionization buffering is unnecessary for the determination of lithium. Nonetheless, the 

precision of this determination is poorer for the coal ash 

than that for silicate rocks and is poorer than that for 

determinations of copper or manganese in coal ash. 

Sodium 

The use of glass volumetric flasks in determinations of sodium in solutions of NBS 1633 produces 

values that are consistently high by 10 to 100 percent. 

Replacement of all glassware with linear polyethylene 

containers eliminates this bias, enabling sodium values 

to agree within 7 percent of literature values. Also, the 

precision for the method is 8-percent relative standard 

deviation. The concentration of sodium in solutions 

from coal ash frequently exceeds the linear range of 

absorbance for the Na 589.0-nm line. However, detection of sodium often requires the use of this line in 

preference to the somewhat less sensitive doublet at 

589.0-589.6 nm. Use of several calibration solutions 

that span a small concentration range enables accurate 

determinations of sodium in the nonlinear portion of the 

calibration curve. 

Magnesium 

The accurate determination of magnesium is quite 

dependent on the dissolution procedure. The use of 

hydrofluoric acid is necessary for the decomposition of 

52 Methods for Sampling and Inorganic Analysis of Coal 

siliceous materials, but the formation of insoluble MgF 2 

can lead to losses of magnesium if the hydrofluoric acid 

is not completely evaporated. The initial fuming of the 

sample in a mixture of nitric and perchloric acids must 

be followed by evaporation in aqua regia and by thorough drying of the resulting residue. Without this 

treatment, losses of magnesium can approach 50 percent. 

Curvature of calibration curves for magnesium 

occurs above concentrations of 0.5 J.tg/mL. With sufficient calibration points, the useful range can be extended 

to 3 J.tg/mL. Concentrations of magnesium in solutions 

of coal ash are rarely high enough to allow the use of the 

202.6-nm line, which is less sensitive (by a factor of 24) 

than the 285.6-nm line. 

Cadmium 

Several factors affect the overall accuracy and 

precision of the cadmium determination. Control of the 

chemical blank is the most important factor. Commonly, acids used for dissolving samples produce blanks 

having cadmium concentrations that greatly exceed 

those of cadmium in solutions of coal ash. Containers 

of such acids should be avoided in sample preparation. 

Adsorption of cadmium on the walls of a 

separatory funnel or a volumetric flask from samples 

having very high concentrations of cadmium can contaminate the next sample placed in the same vessel. 

Thorough cleaning of glassware with 50 percent nitric 

acid, followed by repeated rinsing with distilled water, 

minimizes this type of error. Autosampler cups made of 

linear polyethylene must be used to prevent initial 

contamination from the cups because the slightly coextracted organic phase in the solution dissolves the polystyrene cups. The cups should be cleaned between uses, 

along with the glassware, to avoid cross contamination 

from one sample to the next. The pipet tip of the 

autosampler has been observed to cause cross contamination that results from inadequate rinsing if the sampleto-sample variation of cadmium concentration is 1 ,000-

fold or more. This cross contamination decreases rapidly 

with repeated pipetings and is readily identified by 

making three or more successive absorption measurements at each autosampler position. Concentrations of 

cadmium in coal ashes are directly correlated with zinc 

concentrations. The latter can reach quite high levels in 

coals that are located near ore bodies (Ruch and others, 

1974). 

When cadmium concentrations in the extract are 

expected to be well above the normal calibration range 

for graphite-furnace AAS, that is, above 100 ng/mL, 

flame AAS can be used to minimize the possibility of 

carry-over contamination. As illustrated in table 24, 

high concentrations of cadmium are sometimes encountered in analyses of coal ash. 
Table 24. Some typical concentration rangesa of analytes in coal ashes originating from different regions of the United States 

Concentration Range (p.g/ml) 

Analyte Cd Cu Li Mn Pb Zn 

Appalacian Rangea 0.02- 0.8 27- 980 11 - 760 11 - 5200 3- 590 17- 3800 

Interior Easterna 0.1 - 66 20- 790 12 - 410 41 - 2800 10- 2900 39- 5400 

Interior Westerna 0.1- 700 22- 670 10- 270 32- 4700 25- 6600 36- 100000 

Western a 0.1 - 25 0.8- 1300 0.3- 490 2- 11000 5- 2900 5 - 3700 

Northern Plainsa 0.01 - 32 16- 630 1- 220 7- 11000 5- 680 10- 2500 

Analyzed Samplesb <0.1- 100 5- 3200 11 - 440 29- 11,000 <10- 60 10- 48,000 

Notes c d e f g 

a Source: Robert Finkelman (personal commun., 1987). 

b Concentration ranges observed for more than 280 coal ashes analyzed by AAS in U.S. Geological Survey laboratories. 

c Correlation with Zn is 0.93. 

ct High values in special mineral samples. 

e Variable concentrations; probably dependent on water contact. 

r Wide range in lithotypes. 

g Concentration is very high near ore beds. 

The extraction yield for cadmium varies as a 

function of both pH and extraction time. Extraction for 

5 min at pH 8.5, followed by back-extraction for 10 

min, assures constant yields of 95 ±5 percent for 

solutions prepared for calibration and for solutions of 

coal ashes. Variations in either pH or extraction time 

lead to irreproducible yields that deteriorate the precision of the method. Small changes in these two variables 

and the difficulty of exactly reproducing the chemical 

blank account for the 20-percent relative standard deviation of the method. 

Losses of cadmium occur prior to atomization in 

the graphite furnace if the charring temperature exceeds 

250 °C. Time constants of the Perkin-ElmerR model603 

atomic absorption spectrometer and recorder are too 

long for accurate measurements of fast transient signals 

produced by rapid atomization. A sequence of temperatures for atomization that provides a heating rate 

matched to instrumental time constants is detailed in 

table 19. An increase in heating rate, either by adding 

programmable ramp features or by increasing the final 

atomization temperature above 2100 oc leads to loss of 

the absorption signal. 

Without the extraction of cadmium before AAS 

measurements, serious errors in corrections for background can occur from Ni 228.73-nm, Ni 228.84-nm, 

and Co 228. 78-nm lines that are within the bandpass of 

the spectrometer (Zander, 1976). Moreover, iron produces a severe suppression of the cadmium atomic 

absorption signal, particularly for furnace atomization. 

Results of analyses for NBS 1633a coal ash and 

for four U.S. Geological Survey quality-control samples 

are summarized in table 23. Accuracy for analysis of 

NBS 1633a, as evident from comparisons of results 

from AAS methods with the certified values, is excellent. 

Except for manganese and lead, the determined concentrations agree with NBS-certified values within one 

standard deviation. The reason for the larger disparity 

of manganese and lead values is not apparent. Measured 

concentrations of manganese and lead in NBS 1633 

(table 22) agree with NBS-certified values well within 

one standard deviation. 

REFERENCES 

American Society for Testing and Materials (ASTM), 1984a, 

D3682-78(1983) Standard test methods for major and 

minor elements in coal and coke ash by atomic absorption, in 1984 annual book of ASTM standards, petroleum 

products, lubricants, and fossil fuels, sect. 5, v. 05.05: 

Gaseous fuels, coal, and coke: Philadelphia, ASTM, p. 

458-465. 

-- 1984b, D3683-78(1983) Standard test methods for 

trace elements in coal and coke ash by atomic absorption, 

in 1984 annual book of ASTM standards, petroleum 

products, lubricants, and fossil fuels, sect. 5, v. 05.05: 

Gaseous fuels, coal, and coke: Philadelphia, ASTM, p. 

466-469. 

Gladney, E.S., 1980, Elemental concentrations in National 

Bureau of Standards biological and environmental standard reference materials: Analytica Chimica Acta, v. 118, 

no. 21, p. 385-396. 

Ondov, J.M., Zoller, W.H., Olmez, Ilhan, Aras, N.K., 

Gordon, G.E., Rancitelli, L.A., Abel, K.H., Filby, KH., 

Shah, K.R., and Ragaini, R.C., 1975, Elemental concentrations in the National Bureau of Standards' environmental coal and fly ash standard reference materials: 

Analytical Chemistry, v. 47, no. 7, p. 1102-1109. 

Rowe, J .1 ., and Steinnes, E., 1977, Instrumental activation 

analysis of coal and fly ash with thermal and epithermal 

neutrons, Journal of Radioanalytical Chemistry, v. 37, 

no. 2, p. 849-856. 

Ruch, R.R., Gluskoter, H.J., and Shimp, N.F., 1974, Occurrence and distribution of potentially volatile trace elements in coal: a final report: Illinois State Geological 

Survey, Environmental Geology Notes, no. 72. 

U.S. Environmental Protection Agency (EPA), 1977, Potential pollutants in fossil fuels: Report no. 

EPA-R2-73-249, Esso Research and Engineering. 

The Determination of Selected Elements in Coal Ash by Atomic Absorption Spectrometry 53 
Vajda, Ferenc, 1981, Line absorption of matrix elements as a 

background correction error in atomic absorption spectrometry: Analytica Chimica Acta, v. 128, p. 31-43. 

54 Methods for Sampling and Inorganic Analysis of Coal 

Zander, Andrew, 1976, Factors influencing accuracy in background corrected atomic absorption: American Laboratory, Nov., p. 11. 
THE DETERMINATION OF MERCURY IN WHOLE 

COAL BY COLD-VAPOR ATOMIC ABSORPTION 

SPECTROMETRY 

By Philip J. Aruscavage and Roosevelt Moore 

Abstract 

Concentrations of mercury in coal are determined by 

cold-vapor atomic absorption spectrometry. After decomposition of a 100-mg sample of pulverized coal in a mixture of 

perchloric and nitric acids, Hg II is reduced to the metal by 

stannous chloride. The mercury metal is removed from the 

solution in a stream of nitrogen and subsequently amalgamated with gold chips contained within a quartz tube that is 

located on the axis of a cylindrically wound induction coil. 

Rapid induction heating of the gold amalgam then releases the 

mercury, which is subsequently swept into a quartz cell where 

the peak absorption of Hg I 253.652 nm is measured. The 

determination limit of the method is 10 ng/g. The typical 

precision for measurements of concentrations of mercury is 5-

to 10-percent relative standard deviation. Good accuracy is 

observed for concentrations of mercury determined for the 

National Bureau of Standards reference materials 1632, 1633, 

and 1633a. 

INTRODUCTION 

Although numerous metods exist for the determination of mercury in whole coal and related materials, 

the methods incorporating cold-vapor atomic absorption spectrometry (AAS) are used in many laboratories 

(Babu, 1975; Doolan, 1982; Swaine, 1985). The differences between the various cold-vapor AAS methods 

principally involve the processes used for decomposing, 

evolving, and collecting the mercury vapor prior to AAS 

measurements. 

In the method recommended by the American 

Society for Testing and Materials (ASTM, 1984), a coal 

sample is decomposed in an oxygen bomb that contains 

nitric acid to collect the mercury. The resulting solution 

of mercury in nitric acid is treated with solutions of 

permanganate and hydroxylamine hydrochloride. 

Finally, stannous chloride solution is added to evolve the 

mercury vapor that is directly measured by the coldvapor AAS technique. 

In the method of Doolan (1982), a coal sample is 

heated in a high-temperature (1 ,250° to 1,450 °C) 

oxygen-rich atmosphere within a combustion-tube furnace. The liberated mercury is collected in a 

permanganate-sulfuric acid solution and finally is 

evolved, through reduction by a stannous chloride solution, into the cell of a cold-vapor AAS. Ebdon and 

others (1982) used nonoxidative pyrolysis of coal at 800 

oc to remove mercury prior to its determination by 

atomic fluorescence spectrometry. 

In a procedure used earlier in U.S. Geological 

Survey laboratories (Flanagan and others, 1982), mercury was removed from pulverized coal samples by 

nonoxidative pyrolysis in nitrogen at 900 oc, and the 

evolved combustion products were passed through a 

gas-washing bottle that contained a stannous chloride 

solution. Then, the mercury was amalgamated with gold 

and finally released by induction heating and determined 

by cold-vapor AAS. Although good results were 

obtained for most anthracite and bituminous coal samples, erratic results were commonly observed for mercury in subbituminous coal. Also, subbituminous coals 

produced contamination that was difficult to remove 

from equipment. Because of these problems, a wet 

oxidation procedure was found to be more appropriate. 

A simple decomposition with a mixture of perchloric 

and nitric acids in a Teflon TM digestion vessel gave 

adequate decomposition of coal samples. This conclusion is supported by comparisons of measured mercury 

concentrations with certified values for National Bureau 

of Standards (NBS) reference coal standards. Mercury 

losses from "spiked" coal samples also were negligible. 

The addition of hydrofluoric acid to the decomposition 

solution did not cause an increase in the concentration 

of mercury found in the whole-coal samples. This 

observation indicates that mercury did not remain in the 

undecomposed silicate materials. The addition of dichromate or permanganate to the digestion solution is 

The Determination of Mercury in Whole Coal by Cold-Vapor Atomic Absorption Spectrometry 55 
unnecessary if nitric acid is added to the hot digestion 

solution prior to the addition of distilled water and if the 

solutions do not stand for more than 2 to 3 h. 

In the procedure described here, a 100-mg pulverized coal sample is decomposed by a solution of perchloric and nitric acids in a Teflon TM (PF A) container. 

The dissolved mercury is then reduced with a stannous 

chloride solution and removed from the solution in a 

stream of nitrogen. The free mercury is collected on 5 g 

of gold chips, which then is inductively heated to drive 

the mercury into a 30-cm-long quartz cell where the 

absorption at 253.7 nm is measured. 

EXPERIMENTAL EQUIPMENT AND METHODS 

Equipment 

The arrangement for the cold-vapor AAS instrument is shown in figure 14. Individual apparatus and 

equipment items are listed here. 

1. Teflon TM (PFA) digestion vials, 33 mL. 

2. Aeration flask, Pyrex TM gas washing bottle with 

coarse-fritted cylinder, 250-mL capacity. 

3. Quartz tube, 30-cm long by 7-mm diameter, drawn 

out in the center to approximately 3-mm diameter. 

4. One-way check valves. 

5. Three-way stopcocks, borosilicate glass. 

6. Two-stage pressure regulator (MathesonR model 

8-580) and needle-valve flow regulator for nitrogen gas. 

7. Flowmeter, precision ball-float rotameter with a 

range of 0.1 to 1 L/min. 

8. Induction furnace, LECOR model 521, with fiveturn copper coil of 3-cm diameter. 

9. Mercury monitor system, LDCR model 1235, with 

dual gas quartz cell 30-cm long by 7 .5-mm diameter and cell volume of 13.7 cm3 • 

10. Strip chart recorder, Perkin-ElmerR model 56, 1- to 

10-mV range. 

11. Hot plate. 

A B c D E F G H 

Figure 14. Diagram of arrangement of instrumentation 

for the measurement of mercury in coal. 

56 Methods for Sampling and Inorganic Analysis of Coal 

Reagents 

All chemical reagents are of reagent-grade or 

higher purity. Doubly-distilled water is used in the 

preparation of all solutions. 

1. Perchloric acid, 72 percent. 

2. Hydrochloric acid, 12 N. 

3. Nitric acid, 14 N. 

4. Gold chips, approximately 5 g, 99.99-percent pure, 

0.5-mm diameter. 

5. Mercury metal, high purity. 

6. SnC12 • 

7. 5 percent (w/v) SnC12 in 12 N hydrochloric acid. 

8. Nitrogen gas, 99-percent pure. 

9. Anhydrous magnesium perchiorate (Anhydrone TM) 

Calibration Standards 

1. Prepare an aqueous stock solution containing 1.00 

mg/mL mercury and 10 percent nitric acid by 

dissolving high-purity metallic mercury in nitric 

acid. 

2. Prepare a solution of 10 ~-tg/mL mercury in 5 percent 

nitric acid by diluting an aliquot of the 1 mg/mL 

stock solution. This solution should be freshly 

prepared each month. 

3. Freshly prepare a solution of 0.10 ~-tg/mL mercury in 

5 percent nitric acid each day from the 10 ~-tg/mL 

mercury solution. Six different aliquots of the 0.10 

~-tg/mL solution are pipeted into the aeration flask 

to effect calibration of the instrument. 

Coal Standards 

Coal standards NBS 1630, 1632, 1633, and 1633a 

are used to verify the accuracy of this analytical method. 

PROCEDURES 

Dissolution of Samples 

Weigh 100 mg of air-dried, pulverized (100 mesh) 

coal into a 25-mL screw-cap Teflon TM digestion container. Add 5 mL of concentrated perchloric acid and 5 

mL of concentrated nitric acid, and then heat the 

sample-acid mixture on a hot plate at 150 oc until 2 to 

3 mL of solution remains (3 to 4 h). Add 1 mL of 

concentrated nitric acid to the hot solution, and finally 

add distilled water until the volume of the solution is 

approximately 25 mL. Immediately close the container 

with the screw cap, and mix the contents. 

Determination of Mercury 

Transfer the solution from the Teflon TM container 

to the aeration flask (fig. 14) and adjust the volume to 
approximately 100 mL with distilled water. Add 6 mL of 

5 percent (w /v) SnC12 solution and close the flask. Begin 

the flow of nitrogen (delivery pressure equals 34.5 kPa (5 

psi); flow rate equals 0.5 L/min) into the aeration flask. 

The evolved mercury is collected on the gold chips within 

approximately 3 min. After the collection process is 

completed, turn the first three-way stopcock (fig. 14) to 

the position that allows the nitrogen flow to bypass the 

aeration flask and to pass directly over the gold chips, 

thus removing water vapor from the system (30 s). After 

the system has dried, turn the second three-way stopcock to direct the gas flow through the absorption cell. 

Power from the RF generator is then applied to the 

induction coil for 15.0 s to heat the gold chips, thus 

releasing the amalgamated mercury into the nitrogen 

stream. The mercury subsequently is transported into 

the cell of the mercury monitor system, where the peak 

absorption of Hg I 253.652 nm is measured and recorded 

on a strip chart recorder. The peak absorption signal for 

each sample is used to extrapolate the mercury concentration from a calibration curve established by separately pipeting 0, 5, 10, 15, 20, and 25 ng of mercury 

from a 0.10 J.tg/mL mercury solution into the aeration 

flask, adding the reagents, and recording the corresponding peak absorption signal. 

DISCUSSION 

NBS coal standards 1630, 1632a, and 1633 and a 

U.S. Geological Survey "in-house" coal standard are 

used as control standards in each measurement sequence. 

The detection limit of the method, based on twice the 

standard deviation for 10 determinations of mercury in 

a blank, is 1 ng of Hg, which is equivalent to 10 ng/g in 

a 100-mg sample. The sensitivity of the method is 1.1 

m V /ng of mercury. The long-term precision of the 

method, estimated from repeated measurements of mercury concentrations in these standards over several 

years, is 5- to 10-percent relative standard deviation for 

the concentration range from 50 to 500 ng/g. Both the 

accuracy and precision of the method (table 25) are 

comparable to those for the methods using oxygenbomb combustion (ASTM, 1984) or high-temperature 

oxidation in a tube furnace (Doolan, 1982). The proceTable 25. Concentrations of mercury determined by coldvapor atomic absorption spectrometry for selected coal and 

fly-ash standards 

Sample Material 

NBS 1632 Bituminous Coal 

USGS 24D Subbituminous 

Coal 

NBS 1633 Coal Fly Ash 

NBS 1633a Coal Fly Ash 

Hg Concentration (t-tg/g) 

Measured a Acceptedb 

0.11 ± 0.01 (15) 0.12 ± 0.02 

0.40 ± 0.02 (20) 

0.12 ± 0.01 (15) 0.14 ± 0.01 

0.15 ± 0.01 (15) 0.16 ± 0.01 

a Uncertainty in concentration is the standard deviation for the 

number of measurements indicated in parentheses. 

b Concentrations of mercury in NBS 1632, 1633, and 1633a 

standard reference materials are certified values. 

dure is simple and rapid and is applicable to a wide 

variety of coal samples. 

REFERENCES 

American Society for Testing and Materials (ASTM), 1984, 

D3684-78(1983) Standard test method for total mercury 

in coal by the oxygen bomb combustion- atomic absorption method, in 1984 annual book of ASTM standards, 

petroleum products, lubricants, and fossil fuels, sect. 5, v. 

05.05: Gaseous fuels, coal, and coke: Philadelphia, 

ATSM, p. 470-473. 

Babu, S.P ., 1975, Trace elements in fuel, in Advances in 

chemistry series 141: Washington, D.C., American Chemical Society, 216 p. 

Doolan, K.J ., 1982, The determination of traces of mercury in 

solid fuels by high-temperature combustion and coldvapor atomic absorption spectrometry: Analytica Chimica Acta, v. 140, no. 1, p. 187-195. 

Ebdon, L., Wilkinson, J.R., and Jackson, K.W., 1982, Determination of mercury in coal by non-oxidative pyrolysis 

and cold-vapour atomic-fluorescence spectrometry: Analyst (London), v. 107, p. 269-275. 

Flanagan, F.J., Moore, Roosevelt, and Aruscavage, P.J., 

1982, Mercury in geologic reference samples: Geostandards Newsletter, v. 6, no. 1, p. 25-46. ~ 

Swaine, D.J., 1985, Modern methods in bituminous coal 

analysis: trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 315-346. 

The Determination of Mercury in Whole Coal by Cold-Vapor Atomic Absorption Spectrometry 57 

THE DETERMINATION OF FLUORIDE IN COAL 

BY ION-SELECTIVE ELECTRODE 

By Herbert Kirschenbaum 

Abstract 

A method is described for determining the concentration of fluoride in coal. Coal ash is fused with sodium hydroxide, and the resulting melt is leached with distilled water. This 

solution is diluted with an ammonium citrate buffer to produce a final solution having a pH in the range of 5.5 to 7.0. The 

fluoride concentration then is determined by measurement of 

the potential produced by a fluoride ion-selective electrode. 

The lower limit for determination of fluorine in a 250-mg ash 

sample is 20 p,g/g. The precision of the method is approximately 6-percent relative standard deviation. 

INTRODUCTION 

The method described herein for determining fluoride in coal (Ingram, 1970; Swanson and Huffman, 

1976) requires that coal ash be fused with sodium 

hydroxide and that the resulting melt be leached with 

distilled water, filtered, and then diluted to a fixed 

volume with an ammonium citrate buffer. The pH of the 

resulting citrate-buffered solution must range from 5.5 

to 7.0 for accurate measurement of the fluoride concentration with an ion-selective electrode (ISE). At a pH 

below 5.5, the measurement gives concentrations that 

are biased low because of the complexation of F- by 

H + . A high bias in the measured concentration occurs 

at pH values above 7.0 because of the presence of high 

concentrations of OH- or HC03 -. 

EXPERIMENTAL METHODS AND PROCEDURES 

Equipment 

Measurements are made with an Orion Research 

IonalyzerTM (model 801), equipped with a fluoride-ion 

electrode (model 94-09) and a single-junction calomel 

reference electrode (model 90-01). 

Reagents 

The quality of each chemical reagent is reagent 

grade or better. 

1. Mg0-Mg(N03h solution: Dissolve 38 g of MgO and 

53 g of Mg(N03h in 500 mL of distilled water. 

2. 1 M ammonium citrate solution: Dissolve contents of 

a 454-g bottle of ammonium citrate in 2 L of 

distilled water. The pH of this solution is 4. 7 to 

4.9. 

3. Sodium hydroxide pellets: Baker AnalyzedTM sodium 

hydroxide pellets, low in carbonates. These pellets 

are used in fusions described later. 

4. Sodium fluoride standard: Purify the sodium fluoride 

by first adding from 10 to 15 mL of concentrated 

hydrofluoric acid to 3 g of sodium fluoride in a 

platinum dish. Evaporate the resulting solution to 

dryness on a steam bath. Transfer the purified 

NaF to a polyethylene vial. 

5. Standard A: Prepare a stock solution of 1 ,000 J.tg/mL 

of fluoride in distilled water by first dissolving 

1.105 g of the purified NaF and then by diluting 

the resulting solution to 500 mL. 

6. Standard B: Prepare a 100 J.tg/mL fluoride standard 

by diluting 10.0 mL of standard A to 100 mL. 

7. Standard C: Prepare a 10 J.tg/mL fluoride standard 

by diluting 1.0 mL of standard A to 100 mL. 

8. Calibration standards: Add 2.7 to 3.0 g (16 pellets) of 

NaOH to each of nine 100-mL volumetric flasks. 

Then, add approximately 20 mL of distilled water 

to each flask to dissolve the NaOH pellets. 

The dilutions used to prepare the individual calibration solutions are detailed in table 26. The calibration standard having a F- concentration of 8 J.tg/mL is 

used to equilibrate between all measurements with the 

ISE on standards and samples. When these calibration 

standards are mixed 1 to 1 with the ammonium citrate 

buffer, the F- concentration is diluted to half the value 

given in table 26. 

The Determination of Fluoride in Coal by Jon-Selective Electrode 59 
Table 26. Dilutions for preparation of individual calibration 

standards 

Pipet 

Volume 

(ml) 

0.02 

0.05 

1.0 

0.15 

2.0 

4.0 

8.0 

10.0 

8.0 

8.0 

Procedure 

Standard 

Pipeted 

(B or C) 

B 

B 

c 

B 

c 

c 

c 

c 

B 

B 

Dilute to 

Final Volume 

(ml) 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

Final 

Concentration 

of Fluorine 

(JJ.g/ml) 

0.02 

0.05 

0.10 

0.15 

0.20 

0.40 

0.80 

1.0 

8.0 

8.0 

1. Thoroughly clean each 35-mL zirconium crucible by 

first fusing NaOH within the crucible and then 

washing the crucible in dilute (1 to 1) hydrochloric 

acid. This step is necessary to avoid contamination. 

2. Weigh 0.250 g of pulverized (100 mesh) coal sample, 

and transfer the sample to a 35-mL zirconium 

crucible. 

3. Add 1 mL of isopropanol into the crucible to wet the 

sample. 

4. Add 1 mL of the Mg0-Mg(N03h solution to the wet 

sample and mix with a glass stirring rod. Rinse the 

stirring rod with a little distilled water while 

collecting the rinse solution in the crucible. 

5. Place the crucible into an oven operated at 110 oc 

and dry the sample for 30 min. 

6. Place the zirconium crucible that contains the sample into a muffle furnace and ash the sample in the 

following uninterrupted sequence: 200 oc for 30 

min, 300 oc for 30 min, 400 oc for 90 min, and 

525 oc for 135 min. If the coal is of high rank, 

such as an anthracite, then ash the sample overnight. 

7. Allow the sample to cool to room temperature. Add 

3 g of NaOH (approximately 16 pellets). Fuse in 

the uncovered crucible over an open Meeker burner 

at a "dull-red" temperature for 2 min. 

8. Allow the sample to cool, add 25 mL of distilled 

water to the crucible, and place the crucible on a 

steam bath to leach the fused mass. After heating 

the crucible contents for approximately 30 min, 

transfer the contents of the crucible into a 100-mL 

polyethylene beaker. Do not put the crucible into 

the polyethylene beaker because contamination 

from the outside surface of the crucible is likely to 

occur. 

60 Methods for Sampling and Inorganic Analysis of Coal 

9. Filter the contents of the beaker through a 9-cmdiameter WhatmanR number 40 paper into a 

100-mL volumetric flask. Wash the residue on the 

paper three times with a 1 percent (w/v) NaOH 

solution. Dilute to the 100-mL mark with distilled 

water and mix well. 

10. Pipet 10 mL of the sample solution into a 100-mL 

polyethylene beaker; pipet 10 mL of 1 M ammonium citrate solution into the beaker, and stir the 

resulting solution. Measure the fluoride concentration in this final solution by ISE. As previously 

explained, it is extremely important that the pH of 

this solution be in the range of 5.5 to 7.0. 

Measurements of electrode potentials are accomplished in the following sequence. Prepare each solution 

for measurements in a 100-mL polyethylene beaker a 

few minutes before the potential is measured. Before 

each measurement on a sample solution, equilibrate the 

electrodes for 5 min in a 4 ,ug/mL fluoride solution. 

Remove excess solution from the electrodes by blotting 

with laboratory tissue paper, such as Kim wipe TM, and 

rinse the electrodes with a portion of the prepared 

solution in a 5-mL polyethylene beaker. Place the 

electrodes in the sample solution, and after exactly 10 

min of equilibration, measure the potential produced by 

the fluoride-ion electrode. Typically, the potential ranges 

from 100 to 170 m V. The actual electrode potential has 

been observed to change as the electrodes age. The 

variability of single potential measurements commonly 

is ±0.5 mV. Upon completion of all measurements of 

electrode potentials for samples and calibration standards, graphically establish the functional relation 

between fluoride concentration and electrode potential 

by plotting concentration (in micrograms per milliliter) 

versus measured potential (in millivolts). This plot generally is accomplished on one-cycle semilogarithmic 

paper, as shown in figure 15. For an ash sample weighing 

250 mg, the concentration of fluorine in the sample (in 

micrograms per gram) equals 800 times the concentration of fluoride in solution (in micrograms per milliliter), as extrapolated from the calibration curve (fig. 15). 

0.04 0.05 0.07 0.10 0.15 0.20 0.30 

F- CONCENTRATION, JlQ/mL 

Figure 15. Two typical calibration curves (A and B). 
ACCURACY, PRECISION, AND DElECTABILITY 

Sets of coal-ash samples are always taken through 

the procedure with three blanks and National Bureau of 

Standards (NBS) coal standard reference material1632. 

A fluoride concentration of approximately 10 ~-tg/mL is 

typical for the blank solutions. The mean value for 51 

determinations of fluorine on ash from NBS standard 

reference material 1632 over a 1-year period is 83 ~-tglg, 

with a standard deviation of 5 ~-tgl g. This value agrees 

quite well with 80 ~-tgl g reported by Gladney and others 

(1984) as the median of seven determinations by several 

different methods of analysis. The American Society for 

Testing and Materials (ASTM) method (ASTM, 1984) 

gives a fluorine concentration of 76 ± 10 ~-tglg (Gladney 

and others, 1984). Swaine (1985) noted that the ASTM 

method generally gives lower results than those from 

pyrohydrolysis methods. The lower limit of determination by the ISE method for fluorine in a 250-mg sample 

is 20 ~-tglg. 

REFERENCES 

American Society for Testing and Materials (ASTM), 1984, 

D3761-79(1984) Standard test method for total fluorine 

by the oxygen bomb combustion-ion selective electrode 

method, in 1984 annual book of ASTM standards, petroleum products, lubricants, and fossil fuels, sect. 5, v. 

05.05: Gaseous fuels, coal, and coke: Philadelphia, 

ASTM, p. 474-477. 

Gladney, E.S., Burns, C.E., Perrin, D.R., Roelandts, Iwan, 

and Gills, T.E., 1984, 1982 compilation of elemental 

concentration data for NBS biological, geological, and 

environmental standard reference materials: NBS Special 

Publication 260-88: Washington, D.C., U.S. Government 

Printing Office. 

Ingram, B.L., 1970, Determination of fluoride in silicate rocks 

without separation of aluminum using a specific-ion 

electrode: Analytical Chemistry, v. 42, no. 14, p. 

1825-1827. 

Swaine, D.J., 1985, Modern methods in bituminous coal 

analysis: trace elements: CRC Critical Reviews in Analytical Chemistry, v. 15, no. 4, p. 336-337. 

Swanson, V.E., and Huffman, Claude, Jr., 1976, Guidelines 

for sample collecting and analytical methods used in the 

U.S. Geological Survey for determining chemical composition of coal: U.S. Geological Survey Circular 735, 

p.7-8. 

The Determination of Fluoride in Coal by Jon-Selective Electrode 61 

THE DETERMINATION OF FORMS OF 

SULFUR IN COAL 

By Norma Rait and Philip J. Aruscavage 

Abstract 

Total sulfur, monosulfide (S=), pyritic sulfur (52 =), and 

suI fate sulfur (SO 4 =) concentrations are determined in wholecoal samples. Total sulfur, monosulfide, and sulfate sulfur are 

determined by infrared absorption of the 502 produced by 

combustion of whole coal or of the separated forms of sulfur in 

an oxygen atmosphere. The pyritic sulfur concentration is 

measured indirectly by determining the iron concentration in 

a separated fraction by flame atomic absorption spectrometry. 

The organically bound sulfur concentration is calculated by 

subtracting the sum of the concentrations of monosulfide, 

sulfate sulfur, and pyritic sulfur from the total sulfur content. 

Coke and coal standards are used as control samples for 

measuring the accuracy and precision of the analytical procedures. The precision of the method for each form of sulfur, as 

determined from replicate analyses of standards, is approximately 5- to 1 0-percent relative standard deviation. The determination limit for sulfur is approximately 50 f.lg (30-percent 

relative standard deviation), which is equivalent to a 0.01 

percent sulfur in 0.5 g of coal. 

INTRODUCTION 

Methods are described for the determination of 

total sulfur and of four forms of sulfur in coal (fig. 16): 

monosulfide (S = ), sulfate sulfur (S04 = ), pyritic sulfur 

(S2 = ), and organically bound sulfur. The methods are 

modifications of those proposed by the American Society for Testing and Materials (ASTM) (1984). 

EXPERIMENTAL EQUIPMENT AND METHODS 

Sample Requirements 

The whole-coal samples are received as air-dried, 

80-mesh powders. Typically, 500 mg of sample is 

required for measurements of total sulfur and the four 

forms of sulfur. 

Laboratory, Supplies, and Equipment 

A steam bath in a fume hood is required. All 

chemicals and gases are of reagent-grade quality. Doubly distilled water is required for the preparation of all 

solutions. 

1. Concentrated acids: hydrochloric and nitric. 

2. 1- and 5-percent hydrochloric acid solutions. 

3. 10 percent (w/v) BaC12 solution, approximately 1 

L. 

4. 20 percent (w /v) zinc acetate solution, approximately 1 L. 

5. 50 percent (w /v) NaOH solution, for cleaning glassware. 

6. 30 percent H20 2 solution, for cleaning glassware. 

7. Cylinder of nitrogen gas and two-stage pressure 

regulator. 

8. Cylinder of oxygen gas and two-stage pressure 

regulator. 

9. V20 5 • 

10. Anhydrous magnesium perchlorate (AnhydroneTM). 

11. LECOR model SC-132 sulfur determinator, combustion boats, and accessories. 

12. LECOR coal standards used for calibration: 0.52, 

1.10, 1. 77, and 2.97 percent sulfur. 

13. Alpha Resources, Inc., coke and coal standards 

numbered 771, 772, 774, 775, 780, and 782. These 

materials are analyzed along with samples as 

control standards. 

14. Flame atomic absorption spectrometer, PerkinElmerR model 370. 

15. Iron standard solutions in 5 percent nitric acid: 0.5, 

1, 3,'5, 7, 10, 20, 40, 60, and 100 p.g/mL iron. 

16. Two laboratory hot plate-magnetic stirrer combinations. 

17. Support-lattice frame to be used as a rack for 

equipment for forms of sulfur equipment (fig. 17). 

18. Metal tube with five outlets and one inlet for 

nitrogen and associated Tygon tubing. 

19. Round-bottom flasks, each having a volume of 200 

mL and three necks. The two outside necks have 

The Determination of Forms of Sulfur in Coal 63 
FILTRATE 

Sample (0.5 g) 

30 mL 1 to 5 mL HCI 

DISTILLATION at 80°C 

RESIDUE 

VACUUM FILTER 

RESIDUE 

50 mL 1 to 9 HN03 

DIGESTION at 1 00°C 

VACUUM FILTER 

RESIDUE 

(Pyritic Sulfur) 

Figure 16. Flowchart for the separation of the forms of 

sulfur. 

ground-glass joints 19/38; the center neck has a 

ground-glass joint 24/40 (fig. 18). These flasks are 

cleaned first with a solution of 50 percent NaOH 

and then with a 30 percent hydrogen peroxide 

solution. Finally, they are rinsed with tapwater 

and then with distilled water. 

20. Heating mantel to fit 200-mL round-bottom flask, 

with accompanying Variac to regulate the temperature. 

21. 70-mL test tubes and supporting laboratory jacks to 

raise and lower test tubes (fig. 17). 

22. Thermometer (150 °C) having a ground-glass joint 

10/30 (fig. 18). 

23. Condenser (fig. 18) with ground-glass joint 14/35. 

24. Pyrex TM ground-glass bushing-type reducing adapters, outer joint 24/40, inner joint 14/35 (fig. 18). 

25. Pyrex reducing adapters: 19/38 to 10/30. 

26. Vacuum flasks having volumes of 4 L and 250 mL, 

each fitted with a fritted-glass filter and a filter 

funnel and clamp. Each flask can be attached to a 

small vacuum pump. 

27. Vacuum filters with diameters of 25 and 47 mm and 

a pore size of 0.45 t-tm and made of cellulose 

triacetate containing a small amount of wetting 

agent. 

28. PyrexTM standard-taper 10/30 inner ground-glass 

joint with a tube extension (outer diameter of 8 

mm; length of 130 mm) (fig. 18). 

64 Methods for Sampling and Inorganic Analysis of Coal 

Figure 17. Photograph of setup. (Photograph by Deborah Dwornik.) 

14/35 

) ( 10/30 

\ J 19/38 

ROUND-BOTTOM FLASK 

t 

12cm 

! 

10/30 

t 

13cm 

! ADAPTERS 

10/30 

L-15-~-c--------------~~---~ 

THERMOMETER 

Figure 18. Diagrams of apparatus. 
29. PyrexTM ground-glass stoppers 19/38. 

30. Graduated cylinders: 5, 10, and 50 mL. 

31. Drying oven, maintained at 110 °C. 

32. Volumetric flasks, 200 mL. 

33. Beakers, 250 mL, with 9-cm-diameter SpeedivapTM 

watch-glass covers. 

34. Erlenmeyer flasks, 250 mL, and S-cm-diameter 

watch-glass covers. 

35. Balance with a sensitivity of 0.1 mg. 

Methods 

Total Sulfur 

The total sulfur content of a sample is determined 

by use of the LECOR SC132 sulfur analyzer (LECO 

Corporation, 1980; Kirschenbaum, 1983). Calibration 

of the sulfur analyzer is based on one of the LECO coal 

standards (LECO Corporation, 1980). After calibration, 200 mg of sample is weighed into a combustion 

boat then is placed in the combustion tube. This tube 

operates at a temperature of 1,370 oc in an oxygen 

atmosphere. The oxygen, which flows through the tube 

and over the boat, reacts with sulfur to form S02 • The 

released so2 passes through the infrared absorption 

detector of the sulfur analyzer. After integrating the 

absorption signal over a period of 1 to 2 min, the 

instrument extrapolates and prints out the concentration 

of sulfur. 

Laboratory Setup for the Separation of Forms of Sulfur 

Within U.S. Geological Survey laboratories, the 

forms of sulfur are separated from 10 coal samples 

simultaneously. Ten three-neck, round-bottom flasks 

are placed in heating mantels. The first and fifth flasks 

have thermometers in one side neck (fig. 17), whereas the 

other eight flasks have stoppers in that side neck. Each 

flask has an air-cooled condenser attached to the center 

neck. The spout at the end of the condenser is placed in 

a 70-mL test tube that rests on a laboratory jack. Each 

of the 10 flasks has a bubble tube in one side neck. 

Nitrogen bubbles through each of the solutions in the 

round-bottom flasks and then passes through the condensers and into the test tubes. The rate of bubbling in 

a test tube is regulated by the height of the laboratory 

jack. 

Monosulfide Sulfur Separation and Determination 

1. Place 500 ± 1 mg of sample into each round-bottom 

flask. Use of a larger quantity of sample may 

cause difficulty in later filtering procedures. 

2. Add 25 mL of distilled water to each sample. 

3. Pour 15 mL of 20 percent zinc acetate solution and 

285 mL of distilled water into a beaker. Place a 

magnetic stirring bar in this solution, and set the 

beaker on a hot plate. While stirring the diluted 

zinc acetate solution, add 3 mL of 50 percent 

NaOH solution. Warm, but do not boil, the 

resulting mixture. 

4. Place 40 mL of this alkaline zinc acetate mixture 

into each test tube. 

5. Bubble nitrogen through the system for 15 min to 

remove oxygen. Set the flow of nitrogen in each of 

the test tubes to approximately one bubble per 

second by adjusting the heights of the jacks. 

6. Add 5 mL of concentrated hydrochloric acid to 

each flask. 

7. Switch on the electrical power to the heating mantels, and maintain the temperature in the flasks at 

80 °C. Continue to bubble the nitrogen through 

the system for 90 min. As the solution evaporates 

from a flask, add 5 percent hydrochloric acid to 

maintain the solution level. 

8. Vacuum filter each alkaline zinc acetate mixture 

through a 47-mm filter. 

9. Wash each precipitate thoroughly with doubly distilled water. 

IO. Discard the filtrate. 

II. Place each filter on a mar ked watch glass and then 

transfer the watch glass into a drying oven that is 

maintained at 110 °C. Dry the filters overnight. 

I2. Transfer the dry precipitate on each filter to a 

separate combustion boat. 

13. Place 500 mg of V 20 5 over each precipitate. 

I4. Determine the percent sulfur by use of the LECOR 

sulfur analyzer as described previously. 

15. To determine the concentration of sulfur in a blank, 

place 500 mg of V 20 5 in a combustion boat and 

measure the percent sulfur. Subtract this concentration from the previous result to obtain the 

percent of monosulfide sulfur in the sample. 

Sulfate Sulfur Separation and Determination 

I. Vacuum filter the solution in each round-bottom 

flask through a 25-mm filter. 

2. Wash the residue thoroughly with IOO mL of I 

percent hydrochloric acid. 

3. Place the residue in a 250-mL Erlenmeyer flask, and 

save it for the determination of pyritic sulfur. 

4. Place the filtrate and washings in a 250-mL beaker. 

5. Add distilled water until the volume of liquid in the 

beaker is 200 mL. 

6. Place the beaker on a hot plate, and bring the 

solution to a boil. 

7. Add 5 mL of I 0 percent BaC12 to the boiling 

solution. 

The Determination of Forms of Sulfur in Coal 65 
8. Place a Speedivap TM watch glass on the beaker. Set 

the beaker on the large hot plate, and evaporate 

the solution to dryness (overnight). 

9. Add 150 mL of 1-percent hydrochloric acid to the 

beaker containing dried residue, and bring the 

mixture to a boil. This prevents the formation of 

colloidal BaS04 , which causes difficulty in 

filtering. 

10. Filter the mixture through a 25-mm vacuum filter. 

Wash the beaker with 1 percent hydrochloric acid, 

and filter the wash solution. 

11. Place the filter paper and precipitate on a marked 

watch glass, and dry them overnight in a drying 

oven at 110 °C. 

12. Subsequently, place the filter paper and precipitate 

in a combustion boat. Spread approximately 500 

mg of V 20 5 over the precipitate, and determine the 

sulfur concentration by the sulfur analyzer. Subtract the blank from this result to give the concentration of sulfate sulfur. 

Pyritic Sulfur Separation and Determination 

1. Add 45 mL of distilled water to each of the residues 

in the Erlenmeyer flasks. 

2. Add 5 mL of concentrated nitric acid to each flask. 

3. Place a watch glass on top of each flask, and set the 

flask on a steam bath. Leave the flask on the 

steam bath for 90 min. 

4. Vacuum filter the mixture in each flask through a 

25-mm filter. 

5. Wash the residue with distilled water; discard the 

residue. 

6. Place the filtrate and washings in a 200-mL volumetric flask, and dilute to volume with distilled water. 

7. Determine the iron leached from the sample by the 

nitric acid by flame atomic absorption spectrometry at the following conditions: 248.3 nm, 0.2-nm 

slit width, hollow cathode lamp, and an airacetylene flame (oxidizing lean, blue). 

8. Calculate the percent pyrite sulfur as follows: 

FeS2 = Fe+ + + S2 

Atomic weight S 32.064 amu 

Fe = 55.847 amu 

(2xS) _ 64.128 _ 1 148 Fe 55.847 - • 

Weight of sample = 0.500 g 

Percent of Fe as pyrite in sample = ppm Fe x 0

·

0001 

0.500 

= ppm Fe x 0.0002 

Dilution factor = 200 

Percent pyrite Sulfur = ppm Fe x 0.0002 x 200 x 1.148 

= ppm Fe x 0.04592 

66 Methods for Sampling and Inorganic Analysis of Coal 

Calculation of Organically Bound Sulfur 

Organically bound sulfur is not determined by 

direct analysis but is determined by difference, as is 

shown in the following equation: 

Percent organically bound S = Percent total S 

(Percent monosulfide + Percent sulfate S 

+ Percent pyritic sulfur) 

DISCUSSION 

Tables 27 through 33 present results from determinations of forms of sulfur in coal standards; also 

shown are accepted values and standard deviations for 

replicate measurements. 

Total sulfur concentrations from replicate determinations on nine coke and coal standards are shown in 

table 27. The accepted values (Alpha Resources, Inc., 

1985) were obtained by using the ASTM recommended. 

method for analysis for forms of sulfur (ASTM, 1984). 

The determination of total sulfur, from initial weighing 

of the sample to the result, requires about 3 min. This 

measurement time is comparable to those of other 

instrumental methods; moreover, the time is much less 

than that required for classical methods (Elliot, 1981). 

The determination limit for total sulfur is 0.02 percent 

for a 200-mg sample. The measured concentrations for 

total sulfur are in good agreement with the published 

values, and the precision is approximately 7-percent 

relative standard deviation. 

The mean concentrations and standard deviations 

of monosulfide sulfur obtained for six Alpha ResourcesR coal standards are shown in table 28. The results of 

Table 27. Total sulfur in coal 

Sulfur Concentration (percent) 

Standard Accepteda Measuredb nb 

771 0.59 0.60 ± 0.003 (10) 

772 0.88 0.87 ± 0.01 (9) 

774 0.63 0.65 ± 0.03 (9) 

775 0.89 0.98 ± 0.01 (10) 

780 2.06 2.17 ± 0.03 (11) 

782 3.18 3.33 ± 0.05 (10) 

NBS 1632a 1.58 1.59 ± 0.03 (11) 

NBS 1635 0.33 0.32 ± 0.02 (10) 

NBS 2683 1.85 1.96 ± 0.04 (10) 

a Sources: Accepted sulfur concentrations for standards 771, 

772, 774, 775, 780, and 782 are from Alpha Resources, Inc. (1985). 

Accepted sulfur concentrations for NBS standards 1632a, 1635, and 

2683 are from NBS (1984). 

b Sulfur concentrations measured in U.S. Geological Survey 

laboratories. Values shown for each coal standard are the arithmetic 

mean and standard deviation for n measurements, where n is the 

number in parentheses. 
Table 28. Monosulfide sulfur in coal 

Monosulfide Sulfur Concentrationa (percent) 

Standard Measuredb nb 

771 0.014 ± 0.004 (8) 

772 0.095 ± 0.008 (5) 

774 <0.01 (6) 

775 <0.01 (6) 

780 <0.01 (7) 

782 <0.01 (6) 

a Accepted monosulfide sulfur concentrations not given by 

Alpha Resources, Inc. (1985). 

b Monosulfide sulfur concentrations measured in U.S. Geological Survey laboratories. Values shown for each coal standard are the 

arithmetic mean and standard deviation for n measurements, where n 

is the number in parentheses. For standard 771, three of the eight 

measurements indicated monosulfide sulfur concentrations of <0.01. 

The mean concentration shown is the average of the other five values. 

monosulfide sulfur determinations for the coal standards numbered 774, 775, 780, and 782 are below the 

determination limit of the procedure, which is 0.01 

percent sulfur. 

The sulfate sulfur concentrations determined for 

standards numbered 772, 780, and 782 (table 29) are in 

good agreement with accepted values (Alpha Resources, 

Inc., 1985). Concentrations of sulfate sulfur in standards 771, 774, and 775 are below the determination 

limit of the method. The standard deviations for the 

concentrations measured for standards 772, 780, and 

782 reflect the low precision of measurements in the 

proximity of the determination limit. 

The pyritic sulfur concentrations determined for 

standards 771, 772, 774, 775, 780, and 782 are presented 

in table 30. The agreement between measured and 

accepted values of pyritic sulfur for standard 782 is not 

particularly good. The sample may contain an ironbearing mineral that is incompletely dissolved in hydrochloric acid; thus, the iron appears as pyrite iron in a 

Table 30. Pyritic sulfur in coal 

Pyritic Sulfur Concentration (percent) 

Standard Accepteda Measuredb nb 

771 0.02 0.03 ± 0.03 (5) 

772 0.03 0.02 ± 0.02 (3) 

774 0.13 0.17 ± 0.05 (4) 

775 0.43 0.41 ± 0.06 (5) 

780 0.74 0.80 ± 0.08 (6) 

782 1.19 1.43 ± 0.22 (4) 

a Source: Accepted pyritic sulfur concentrations for standards 

are from Alpha Resources, Inc. (1985). 

b Pyritic sulfur concentrations measured in U.S. Geological 

Survey laboratories. Values shown for each coal standard are the 

arithmetic mean and standard deviation for n measurements, where n 

is the number in parentheses. 

Table 29. Sulfate sulfur in coal 

Sulfate Sulfur concentration (percent) 

Standard Accepted a Measuredb nb 

771 0.01 <0.01 (7) 

772 0.03 0.035 ± 0.012 (5) 

774 0.01 <0.01 (6) 

775 0.01 <0.01 (7) 

780 0.13 0.13 ± 0.05 (6) 

782 0.06 0.046 ± 0.046 (7) 

a Source: Accepted sulfate sulfur concentrations for standards 

are from Alpha Resources, Inc. (1985). 

b Sulfate sulfur concentrations measured in U.S. Geological 

Survey laboratories. Values shown for each coal standard are the 

arithmetic mean and standard deviation for n measurements, where n 

is the number in parentheses. 

subsequent digestion with nitric acid. Iron-bearing minerals likely to occur in coal include siderite, hematite, 

marcasite, and goethite (Elliot, 1981). Pyritic sulfur, 

after oxidation by nitric acid and precipitation with 

BaC12 , is determined as previously described for sulfate 

sulfur (table 31). Results for organically bound sulfur, 

which is determined on the filtered residue, appear in 

table 32. Calculations of organically bound sulfur (table 

33) are in good agreement with the accepted values. 

As illustrated by data in table 31, the concentrations determined for pyritic sulfur in standard 782 is 

again higher than the accepted value, but the value for 

organically bound sulfur in standard 782 (table 32) is 

lower. This observation indicates that the accepted 

concentration for pyritic sulfur may be low. However, 

organically bound sulfur may have been oxidized in the 

nitric acid digestion, thus, giving high values for pyritic 

sulfur in our determinations. Because the measurements 

of sulfur in standards 771 and 772 are near the determination limit of the method, the precision is low. 

Table 31. Pyritic sulfur in coal by direct method 

Pyritic Sulfur Concentration (percent) 

Standard Measured a nb 

771 0.018 ± 0.003 (3) 

772 0.017 ± 0.004 (3) 

774 0.17 (2) 

775 0.39 (2) 

780 0.87 (2) 

782 1.47 (2) 

a Source: Standards are from Alpha Resources (1985). 

b Pyritic sulfur concentrations measured in U.S. Geological 

Survey laboratories. Values shown for each coal standard are the 

arithmetic mean and standard deviation for n measurements, where n 

is the number in parentheses. 

The Determination of Forms of Sulfur in Coal 67 
Table 32. Organically bound sulfur in coal by direct method 

Organic SuI fur Concentration (percent) 

Standard Measureda nb 

771 0.56 ± 0.02 (3) 

774 0.49 (2) 

775 0.59 (2) 

780 1.08 (2) 

782 1.61 (2) 

a Source: Standards are from Alpha Resources, Inc. (1985). 

b Organic sulfur concentrations measured in U.S. Geological 

Survey laboratories. Values shown for each coal standard are the 

arithmetic mean and standard deviation for n measurements, where n 

is the number in parentheses. 

REFERENCES 

Alpha Resources, Inc., 1985, Certification of ultimate coal and 

coke standards: Stevensville, Michigan, Alpha Resources, 

Inc. 

American Society for Testing and Materials (ASTM), 1984, 

1984 annual book of ASTM standards, petroleum products, lubricants, and fossil fuels, sect. 5, v. 05.05: Gaseous fuels, coal, and coke: Philadelphia, ASTM, p. 

350-354. 

Elliot, Martin, ed., 1981, Chemistry of coal utilization, (2d 

68 Methods for Sampling and Inorganic Analysis of Coal 

Table 33. Organically bound sulfur in coal by indirect 

method 

Organic Sulfur Concentration (percent) 

Standard Accepted a Measuredb nb 

771 0.56 0.55 ± 0.03 (4) 

772 0.75 0.69 (1) 

774 0.49 0.48 ± 0.03 (3) 

775 0.45 0.53 ± 0.03 (3) 

780 1.19 1.27 ± 0.08 (3) 

782 1.93 1.76±0.18 (3) 

a Source: Accepted organic sulfur concentrations are from 

Alpha Resources, Inc. (1985). 

b Organic sulfur concentrations measured by difference in U.S. 

Geological Survey laboratories. Values shown for each coal standard 

are the arithmetic mean and standard deviation for n measurements, 

where n is the number in parentheses. 

suppl. volume): New York, Wiley-Interscience, p. 

386-391, 415, 416. 

Kirschenbaum, Herbert, 1983, The classical analysis of silicate 

rocks-the old and the new: U.S. Geological Survey 

Bulletin 1547, p. 48-49. 

LECO Corporation, 1980, Instruction manual SC-132 sulfur 

system: St. Louis, Missouri. 

NBS Standard Reference Materials Catalog 1984-1985, 

National Bureau of Standards (NBS), 1984, Special Publication 260, Washington, D.C., U.S. Government Printing Office. 
APPENDIX: REFERENCE MATERIALS FOR 

COAL ANALYSIS 

By D.W. Golightly and F.O. Simon 

The following tabulations list some of the reference materials available for use in the chemical analysis 

of coal. Data given in these tables are intended only to 

illustrate the degree to which the individual materials 

have been characterized. The analyst should always refer 

to specific certificates of analysis or other data provided 

directly by the supplier of the reference materials used. 

Several coal standards now are being (or only 

recently have been) prepared by different laboratories; 

plans for preparation of these materials and available 

data are included in this section to alert the reader to 

these developments. The most significant program underway for the preparation and distribution of new coal 

standards is the Premium Coal Sample Program at 

Argonne National Laboratory. This program, described 

later, has produced eight new coal standards collected, 

analyzed, processed, and maintained for distribution to 

the coal research community. Important new coal and 

coal-ash standard reference materials for trace elements 

and radioactivity are expected to be available from the 

International Atomic Energy Agency in 1988. Also, the 

U.S. Geological Survey is preparing a new trace-element 

coal standard; preliminary data for this sample are 

included in this appendix. 

SULFUR IN COAL: NBS STANDARDS 2682 

THROUGH 2685 

Sulfur Furnace Ash 

SRMa Coal Type % % 

2682 Sub bituminous 0.47 6.37 

2683 Bituminous 1.85 6.85 

2684 Bituminous 3.00 11.09 

2685 Bituminous 4.62 16.53 

a SRM: Standard Reference Material. 

b Moisture free. 

Higher Heating 

Valueb MJ/kg 

27.08 

32.58 

29.21 

27.61 

These SRMs are intended primarily for use as analytical standards for the determination of total sulfur in coal, ash content, and 

calorific value. Semiquantitative data for these SRMs are available 

from NBS on 32 elements, including carbon, hydrogen, and nitrogen. 

Source: National Bureau of Standards (NBS) certificate of 

analysis for standard reference materials 2682, 2683, 2684, and 2685, 

February 25, 1985. 

TRACE MERCURY IN COAL: NBS STANDARD 

1630 

Mercury concentration = 0.13 p.g/g 

NBS-SRM 1630 is intended to be an analytical standard for the 

determination of trace mercury in coal. It consists of a commercially 

available coal crushed to particle size of 210 to 500 ,urn. 

The concentration of selenium in this SRM is reported to be 2.1 

,uglg, but the value is not certified by NBS. 

Source: National Bureau of Standards (NBS) certificate of 

analysis, August 1, 1979. 

CONCENTRATIONS OF ELEMENTS IN NBS-SRM 

COALS AND COAL FLY ASHa 

Element or 

Property 

Al(o/o) 

As 

Ba 

Be 

Br 

C(total, %) 

Ca 

Cd 

Ce 

Cl 

Co 

Cr 

Cs 

Cu 

Eu 

Fe(%) 

Ga 

H(%) 

Hf 

Hg 

K(%) 

La 

Li 

Mg(%) 

Mn 

Concentration, ,ug/gb 

1632b 1635 1633a 

0.855 

3.72 

67.5 

(17) 

78.11 

0.204 

0.0573 

(9) 

(1260) 

2.29 

(11) 

(0.44) 

6.28 

(0.17) 

0.759 

5.07 

(0.43) 

0.0748 

(5.1) 

(10) 

0.0383 

12.4 

(0.32) 

0.42 

0.03 

(3.6) 

(0.65) 

2.5 

3.6 

(0.06) 

0.239 

(1.05) 

(0.29) 

21.4 

14.3 

145 

(0.15) 

(12) 

1.11 

1.0 

(180) 

(46) 

196 

(11) 

118 

(4) 

9.4 

(58) 

(8) 

0.16 

1.88 

0.455 

179 

Appendix: Reference Materials for Coal Analysis 69 
Mo 

N(07o) 

Na(%) 

Ni 

Pb 

Rb 

S(%) 

Sb 

Sc 

Se 

Si(%) 

Sm 

Sr 

Th 

Ti(%) 

Tl 

u 

v 

w 

Zn 

Ash(%) 

Calorific Value 

(MJ/kg) 

(0.9) 

1.56 

0.0515 

6.10 

3.67 

5.05 

1.89 

(0.24) 

(1.9) 

1.29 

(1.4) 

(0.87) 

(102) 

1.34 

0.0454 

0.436 

(14) 

(0.48) 

11.9 

6.79 

32.57 

(0.24) 

1.74 

1.9 

0.33 

(0.14) 

(0.63) 

0.9 

0.62 

(0.02) 

0.24 

5.2 

4.7 

(29) 

0.17 

127 

72.4 

131 

(0.18) 

6.8 

(40) 

10.3 

22.8 

830 

24.7 

(0.8) 

5.7 

10.2 

297 

220 

a Source: National Bureau of Standards (NBS) certified values 

and information values, in parentheses, are from the following 

certificates of analysis: 

1632b- Bituminous coal from Osage, W.Va., June 20, 1985. 

1635- Subbituminous coal from Erie, Colo., August 22, 1979. 

1633a- Coal fly ash from Pennsylvania and West Virginia coals, 

January 5, 1985. 

Further information and data on NBS standards are available 

from the following sources: 

Gladney, E.S.,and others, 1984, standard reference materials: 

1982 compilation of elemental concentration data for NBS biological, 

geological, and environmental standard reference materials: NBS 

Special Publication 260-88, Washington, D.C., U.S. Government 

Printing Office, 221 pp. 

Taylor, J.K., 1985, Standard reference materials: handbook for 

SRM users: NBS Special Publication 260-100, Washington, D.C., 

U.S. Government Printing Office, 85 pp. 

National Bureau of Standards, 1984 Standard reference materials catalog 1984-85: NBS Special Publication 260, Washington, D.C., 

U.S. Government Printing Office. 

Office of Standard Reference Materials, Room B311, Chemistry 

Building, National Bureau of Standards, Gaithersburg, MD 20899, 

telephone 301-921-2045. 

b Concentration units are percent, that is, centigrams per gram, 

for the elements Al, C, Fe, H, K, Mg, N, Na, S, Si, and Ti and for ash. 

MINTEK COAL STANDARDS: SOUTH AFRICAN 

REFERENCE MATERIALSa 

Element Concentration, P-'fil 

SARM 18 SARM 19 SARM 20 

Al(%) 1.36 4.24 5.96 

As 7 4.7 

B (30) (90) (90) 

70 Methods for Sampling and Inorganic Analysis of Coal 

Ba 78 304 372 

Be 4.1 2.8 2.5 

Br (3) (2) (2) 

Ca(%) 0.13 0.99 1.34 

Ce 22 56 87 

Cl (32) 

Co 6.7 5.6 8.3 

Cr 16 50 (67) 

Cs (1) 1.4 (2) 

Cu 5.9 13 18 

Eu (0.3) (0.7) (1) 

Fe(%) 0.20 1.22 0.82 

Ga (8) 14 16 

Ge (8) 13 

Hf 1.7 5.4 4.8 

Hg (0.04) (0.2) (0.25) 

K(%) 0.12 0.20 0.12 

La 10 27 43 

Li (11) (37) (90) 

Mg(%) 0.066 0.12 0.26 

Mn 22 157 80 

Mo (1) (2) 

Na(%) 0.0130 0.22 0.20 

Nb (6) (10) (16) 

Ni 10.8 16 25 

p 30 130 610 

Pb (5) 20 26 

Rb 8.1 9 10 

S(%) 0.56 1.49 0.51 

Sb (0.3) (0.3) (0.4) 

Sc 4.3 7.6 10 

Se (1) 0.8 

Si(%) 2.90 7.01 8.26 

Sm 2.0 4.9 6.3 

Sn (1.0) (3) (4) 

Sr 44 126 330 

Ta (0.3) (0.8) 1.2 

Tb (0.3) (0.7) (0.9) 

Th 3.4 12 18 

Ti(%) 0.0683 0.204 0.38 

u 1.5 5 4 

v 23 35 47 

w (2) (2) (3) 

y (12) (20) 29 

Yb (2) (2) 

Zn 5.5 12 17 

Zr 67 351 (180) 

L.OJ.{%)c 90.11 71.28 64.66 

a SARM: South African reference material. 

b Concentration units are micrograms per gram, unless indicated 

otherwise. 

c L.O.I.: Loss on ignition. 

SARM 18 is a high-volatile, low-rank bituminous coal with a 

rank in the vitrinite category V 7 • 

SARM 19 is a subbituminous to bituminous coal and is of generally 

very low rank (average V 4). 

SARM 20 is a subbituminous to bituminous coal and is of generally 

low rank (average V6). 

Petrographic information is provided by Ring and Hansen (1984) on 

each SARM. 

Source: Ring, E.J. and Hansen, R.G., 1984, The preparation of three 

South African coals for use as reference materials: MINTEK Report 

No. M169, 130 p. Council for Mineral Technology, 200 Hans Strijdom 

Road, Randburg, South Africa. 
BCR REFERENCE MATERIALS 

CRM 065 Coal 

Property 

Ash 

Sulfur 

Calorific Value 

Certified Value 

39.1 mg/g 

8.3 mg/g 

34.915 kJ/g 

95% Conf. Interval 

0.6 mg/g 

0.2 mg/g 

0.070 kJ/g 

Source: Catalogue of BCR Reference Materials, Commission of 

the European Communities, Community Bureau of Reference, Brussels, 1982. 

CRM 038 Fly Ash from Pulverized Coal 

Certified 95% Confidence 

Concentration Limit, p,g/g 

Element p,g/g 

As 48.0 2.3 

Cd 4.6 0.3 

Co 53.8 1.9 

Cu 176 9 

Fe 338.10 7.10 

Hg 2.10 0.15 

Mn 479 16 

Na 374.10 15.10 

Pb 262 11 

Zn 581 29 

Particle size = 0.5 to 10 p,m. 

Source: Addendum to the Catalogue of BCR Reference 

Materials. 

PREMIUM COAL SAMPLE PROGRAM, 

ARGONNE NATIONAL LABORATORY 

This program was established to provide a suite of 

eight different premium coal samples to serve as standards for comparison. Coal samples designated 

"premium" have been selected, collected, transported, 

processed, and stored, while the original conditions were 

closely maintained. The coals selected represent a range 

of coalification, maceral content, mineral composition, 

and commercial significance. Each sample is kept in an 

inert atmosphere during transportation and in all processing steps. Prepared samples are sealed in glass 

ampoules and carboys. Each coal has been characterized 

by physical and chemical methods. The analyses planned 

include proximate, ultimate, calorific value, sulfur 

forms, Gieseler plasticity, and others. Information is 

available from the manager of the Premium Coal Sample Program: Dr. Karl S. Vorres, Chemistry Division, 

Building 211, Argonne National Laboratory, 9700 South 

Cass Avenue, Argonne, IL 60439, telephone 

312-972-7374. 

COAL AND COAL ASH STANDARDS FOR TRACE 

ELEMENTS AND RADIOACTIVITY, INTERNATIONAL ATOMIC ENERGY AGENCY 

Reference materials for trace elements and radioactivity will be available in 1988. Information is available through Dr. R. Schelenz, Head, Chemistry Unit, 

Analytical Quality Control Services, International 

Atomic Energy Agency, P.O. Box 100, A-1400 Vienna, 

Austria. 

TRACE METALS IN COAL 

Alpha Resources, Inc. 

Element Concentrationa, p,g/g Methodb 

Ag 

As 

B 

Be 

Cd 

Co 

Cr 

Cu 

F 

Ga 

Ge 

Hg 

Li 

Mn 

Mo 

Ni 

Pb 

Sb 

Se 

Sr 

Tl 

v 

Zn 

AR-1800 AR-1801 AR-1802 AR-1803 

0.3a 0.3a 0.3a 0.3a c 

5.0 6.1 52.0 4.8 A 

129 118 131 60 B 

3.9 3.3 3.9 0.3 c 

0.2a 0.2a 0.2a 0.2a c 

15 11 7 1 c 

25 20 19 4 c 

24 18 19 10 c 

83 68 62 46 D 

15a 15a 15a 15a c 

15 15 13 c 

0.03 0.04 0.32 0.05 E 

32 17 13 4 c 

15 14 33 11 c 

2 2 3 la c 

82 58 22 5 c 

8 8 64 4 c 

0.9 0.9 0.8 1.2 A 

2.4 2.6 3.0 0.5 F 

92 127 114 558 G 

3a 3a 3a 3a c 

53 28 36 11 c 

51 109 23 3 c 

a Concentration reported is at or below detection limit for 

method. 

b Method: 

A. HF-HCl digestion; gaseous hydride generation atomic 

absorption spectrometry (AAS). 

B. Na2C03 fusion of ash; curcumin colorimetric. 

C. ASTM D3683-78-AAS. 

D. ASTM D3 761-79 oxygen-bomb combustion; 

ion-selective electrode. 

E. ASTM D3684-78; oxygen-bomb combustion. 

F. Oxygen-bomb combustion; gaseous hydride generation 

AAS. 

G. HF-HCl dissolution; flame emission. 

Alpha Resources, Inc., also has available coal standards for 

sulfur, with concentrations of sulfur that range from 0.2 to 6 percent 

sulfur, and 11 coal standards for sulfur forms (pyritic, sulfate, 

organic, and total sulfur). The latter standards have been characterized for proximate analysis (ash, volatile matter, fixed carbon, and 

calorific value), for ultimate analysis (carbon, hydrogen, nitrogen, 

chlorine, and ash), and for oxides (P20 5 , Si02 , Fe20 3 , Al20 3 , Ti02 , 

CaO, MgO, S03, K20, Na20). 

Alpha Resources, Inc., Box 199, Stevensville, MI 49127. 

Appendix: Reference Materials for Coal Analysis 71 
U.S. GEOLOGICAL SURVEY COAL STANDARD: 

Preliminary Data for Whole Coala 

Element Concentration, 118/gb 

As 20 

Ba <90 

Br 61 

Ce 8 

Co 4.1 

Cr 8.2 

Cs 0.2 

Eu 0.19 

Fe(OJo) 0.73 

Hf 0.3 

Hg 0.14 

K(OJo) <0.30 

La 5 

Lu 0.07 

Na(OJo) 0.02 

Nd <20 

Rb <20 

Sb 0.9 

Sc 1.5 

Se 1.9 

Sm 0.7 

Sr 38 

Ta 0.13 

Tb 0.14 

Th 1.2 

u 0.4 

w <2 

Yb 0.5 

Zn 43 

a Preliminary data are from instrumental neutron activation 

analysis of whole coal, September 1983; S. Mee, analyst. 

b Concentration units are percent, that is, centigrams per gram, 

for the elements Fe, K, and Na. 

72 Methods for Sampling and Inorganic Analysis of Coal u U.S. GOVERNMENT PRINTING OFFICE: 1989 - 242-338 - 226/80058 
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