Atomic-Absorption 

Methods of Analysis 

Useful in Geochemical 

Exploration

By F. N. WARD, H. M. NAKAGAWA, T. F. HARMS, and G. H. VAN SICKLE 

GEOLOGICAL SURVEY BULLETIN 1289

A compilation of atomic-absorption 

methods yielding data on geologic 

materials useful in geochemical 

prospecting for ore deposits

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 76-603254

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.G. 20402 - Price 30 cents (paper cover)
CONTENTS

 Page

Abstract. ___-___-_-_--____-----_-_______-_--__-____-___-_______ 1

Introduction.______________________________________________________ 1

Atomic-absorption determination of the constituents.__._---_---___--__ 9 

Silver, bismuth, cadmium, lead, copper, zinc, cobalt, and nickel in

rocks and soils._________________________________________ 9

General procedure.____-_____-.___-_-_--._-___--___________ 9

Specific procedures_______________________________________ 11

Silver_._._____________._..._.______ 11

Bismuth________---________--___-_-_--_----_____._ 12

Cadmium___________________________________________ 14

Lead_______________________________________________ 15

Copp er_ ____________________________________________ 17

Zinc._--_--_----_---_______________________________ 20

Cobalt. ..________.___----____._--._._____ 22

Nickel... ____________________________-.__ 23

Calcium in rocks, soils, and plant ash, and lithium, potassium, and

sodium in rocks and soils____________.____________________ 25

General procedure._____-__________-__-_-_-_-____-________- 25

Specific procedures_______________________________________ 26

Calcium in rocks and soils___-_-______--_-_----____-___- 26

Calcium in plant ash______________-_--__-__--_-___._- 28

Lithium in rocks and soils__-______--__-___-----_-_____- 28

Potassium in rocks and soils____________________________ 30

Sodium in rocks and soils__________________-___________- 31

Gold, tellurium, and mercury in rocks and soils ___________________ 33

Specific procedures_______________________________________ 33

Gold .....____-____-....___--__--______-_-__-._____ 33

Tellurium....__________________________ 38

Mercury___________________________________________ 41

References cited.____-___-_-___-_--_____-___-__-_--_____-_______-__ 42

TABLES

 Page

TABLE 1. Determination of copper content of soils by colorimetric and

atomic-absorption methods....__________________________ 6

2. Atomic-absorption analysis of fir ash_______________________ 6

3. Minimum concentrations detectable by methods useful in 

geochemical exploration and average contents of the elements 

in soils, basalts, and granites._______--___-.___-__-_____- 7

4. Lead content of rocks and minerals--_--___-___-_-__________ 16

5. Repeatability of lead determinations on rocks and minerals._ 16

6. Copper content of rocks and minerals...........____________ 18

7. Repeatability of copper determinations on rocks and minerals.. 19

8. Zinc content of rocks and minerals.________________________ 20

9. Repeatability of zinc determinations on rocks and minerals.- 21

in

ATOMIC-ABSORPTION METHODS OF 

ANALYSIS USEFUL IN GEOCHEMICAL 

EXPLORATION

By F. N. WARD, H. M. NAKAGAWA, T. F. HARMS, and 

G. H. VANSICKLE

ABSTRACT

Atomic-absorption methods for determining 15 elements in soils and rocks 

are described in sufficient detail for use by nontechnical persons. These elements 

are silver, bismuth, cadmium, copper, lead, zinc, cobalt, nickel, calcium, lithium, 

sodium, potassium, gold (three methods), tellurium, and mercury. A few of 

these methods are modified from published procedures for use on geologic materials other than natural waters; the remaining ones have been developed in the 

U.S. Geological Survey laboratories.

Insofar as possible, sample dissolution is accomplished by digestion with hot 

nitric acid, but in certain samples, for example gold and tellurium, dissolution 

is accomplished by different combinations of hydrobromic acid and bromine, 

and in other samples, for example alkalis and calcium, dissolution is accomplished 

by perchloric, nitric, and hydrofluoric acid mixtures. Sample dissolution for the 

mercury determination is replaced by the application of heat to evolve the 

element or decompose its compounds. The methods differ in the judicious use 

of solvent extraction to separate the elements from possible interferences, to 

achieve a relatively uniform matrix, and to enrich the element above a threshold 

concentration amenable to atomic-absorption measurement;

Most of these procedures include short introductory statements of documentation and additional references as well as comments on the most common interferences when applied to soils and rocks.

INTRODUCTION

All the analytical methods described in this report are based on 

atomic-absorption spectrometry. They were devised primarily to 

increase the analytical capacity of the U.S. Geological Survey laboratories, especially to meet the needs of an expanded program to develop 

means to "identify exploration targets" as sources of certain strategic 

minerals (U.S. Geol. Survey, 1968). Some of the methods have been 

published (Huffman and others, 1966; Nakagawa and Harms, 1968; 

Nakagawa and Thompson, 1968; Thompson and others, 1968; Ward 

and Nakagawa, 1967); other methods are being processed for publication; and all the methods are still being investigated and improved 

not only to achieve greater sensitivity but also lo permit application 

to a greater variety of geologic materials. The purpose in bringing 

the methods together in this report is to make them generally available 

to interested workers both in and out of the U.S. Geological Survey.

1
2 ATOMIC-ABSORPTION METHODS OF ANALYSIS

The principles of atomic-absorption measurement are relatively 

simple so simple in fact that, as Kahn (1966) noted, they are "at 

least on the surface, too simple to be interesting." The sample for 

analysis is dispersed in a beam of energy, usually from a hollowcathode lamp, and atoms in the ground state absorb the incident 

energy of certain discrete frequencies, which are called resonant 

frequencies. The absorption causes a decrease in emerging energy, 

and with suitable instrumentation the decrease can be measured 

relative to the incident beam or other reference and related to the 

concentration of the given element dispersed in the beam and ultimately to the amount of the element in a geologic sample.

Available instruments have a great many features, all of which 

are used at one time or another. Certain instruments measure the 

percentage of absorption relative to the incident energy, and others 

actually measure the absorbance (negative logarithm of transmission) 

by taking advantage of the fact that the voltage across a semiconductor diode is linear with respect to the direct current passing 

through the diode. Several commercial instruments offer built-in 

scale expansion, and others provide this feature by an accessory 

recorder. Some instruments with direct readouts provide for zero 

suppression which is advantageous for measuring concentrations in 

a given range, for example, from 3 to 8 ppm (parts per million).

Atomic-absorption methods are limited by the radiation sources, 

the sampling devices used to introduce the sample into the beam of 

radiation from the source, and the system usually optical for 

isolating the absorption frequencies.

Hollow-cathode lamps that provide emitted energy of well-defined 

frequencies are the most common radiation source. Other types of 

lamps, for example Osram, that emit a continuum were formerly used, 

especially for alkali determinations. Single-element hollow-cathode 

lamps have proved more useful than the multielement lamps. The 

single-element lamps not only have greater intensity and hence 

greater sensitivity, but also avoid the possibility of spectral interference due to closely spaced resonance frequencies, especially when 

cathodes are made from pure materials. Combinations of elements 

in multielement lamps are accordingly limited and often fail to satisfy 

the needs of more than one or two laboratories.

Initially the dispersion of monochromators ranged from 5 to 60 

angstroms per millimeter, and over the range of a given monochromator the bandpass ranged from 15 to 60 A, but the need for efficient 

monochromators seemed unimportant because of the selectivity 

provided by the hollow-cathode lamps. However, the widespread 

application of atomic-absorption techniques to different materials 

and the increase in the number of elements determined on such
INTRODUCTION 6

materials intensified the need for better resolution in the monochromator. This need was met by resonance detectors, introduced 

by Sullivan and Walsh (1965, 1966), which isolate the resonant 

radiation frequencies characteristic of the element being measured. 

Such resonant radiation is within a Doppler width of the excitation 

frequency, and for copper the width is of the order of 0.01 A. Amos 

(1967a) stated that "Observation of this radiation corresponds to a 

monochromator-detection system with a bandpass of about 0.02 A."

These resonance detectors are based on the fact that ground-state 

atoms in an atomic vapor that is produced thermally or by a sputtering 

technique absorb resonant frequencies from an incident atomic 

spectrum. Atoms absorbing the resonant frequencies become excited 

for a finite time and during that time undergo reorientation, probably 

because of collisions. Ultimately they return to the ground state 

and in doing so emit isotropic radiation of the same resonant frequency 

as absorbed from the incident atomic spectrum.

In the assembled instrument the element being analyzed is atomized 

into the path of the atomic spectrum that is produced by a highintensity hollow-cathode lamp, and the ground-state atoms absorb 

resonant frequencies proportional to the quantity of the element 

present. The variations in the absorbed frequencies govern the number 

of the atoms excited in the atomic vapor and hence the isotropic 

radiation from the atomic vapor. That radiation is detected by a 

photomultiplier placed at right angles to beam of the atomic spectrum 

and read out in the usual manner; however, phase-sensing detection 

techniques may be applied to the photomultiplier current to further 

enhance the signal-to-noise ratio and to improve the overall sensitivity.

The sampling device, which produces ground-state atoms of the 

element being measured, most commonly consists of a burner and 

nebulizer designed to atomize a solution of the element. For mercury 

because of the volatility of the element at ambient temperatures the 

need of a burner and nebulizer assembly is virtually eliminated. 

Infrequently other elements are volatilized by heat, and the vapor is 

passed into an absorption chamber. Venghiattis (1967) proposed to 

mix a sample with a solid fuel and oxidizer and to burn the pelletized 

mixture in the light path of a hollow-cathode lamp. His technique 

avoids clogging that may occur when solutions with gangue material 

are nebulized in the conventional burner, and it eliminates memory 

effects due to attack of burner by strong acid solutions; however, the 

flame of the fuel and oxidizer produces a continuum that tends to 

lower the sample-to-background ratio and the resulting sensitivity. 

Each of the above techniques is applicable to certain types of samples, 

but the most useful and by far the most common means of introducing 

a sample into the light path consists of nebulizing an aqueous solution
4 ATOMIC-ABSORPTION METHODS OF ANALYSIS

of the element into an acetylene-air flame. The aqueous solution is 

homogeneous as compared to the pelletized sample and oxidizer 

mixture, and it volatilizes at a uniform rate when properly nebulized.

The premix or laminar-flow burner and the total-consumption or 

diffusion-type burner are commonly used in atomic-absorption 

spectroscopy. The premix burner generally uses acetylene-air mixtures that burn quietly and reproducibly. The total-consumption 

burner generally uses hydrogen-air mixtures that under optimum 

conditions burn with an ear-splitting noise that even the best of 

engineering fails to suppress. Although the name total-consumption 

burner suggests a greater efficiency than the name premix, both 

burners are only about 5 percent efficient (Kahn, 1966). In the totalconsumption burner the turbulent flow permits only the smallest 

droplets of nebulized sample solution to be dehydrated and burned, 

and in the premix burner the larger drops fall out in the mixing 

chamber and drain away, and again only the smallest droplets are 

dehydrated and burned.

The advantages of atomic-absorption methods over other analytical 

methods far outweigh the disadvantages (Amos, 1967b). Atomicabsorption methods are extremely sensitive (see definition of sensitivity on p. 7) for such elements as beryllium, copper, cobalt, 

magnesium, calcium, lithium, and zinc. They are also very precise 

generally within ±1 percent (Billings and Adams, 1964). Most 

commercial instruments used in these methods are equipped with 

direct readouts or can be so adapted, and they provide specificity 

and selectivity by the energy source a hollow-cathode lamp or, 

more recently, a resonance detector as described above.

The disadvantages of atomic-absorption methods, aside from instrumental limitations, result primarily from the matrix that contains 

the element measured. These matrix problems consist of (1) interelement effects caused by the presence of different amounts of gangue 

elements initially present in or added to the sample during dissolution 

and (2) effects resulting from specific properties of the solvent or 

dispersant. Interference caused by interelement effects may be further 

defined as chemical, spectral, ionization, and molecular and particulate absorption.

Chemical interference includes compound formation in the flame 

the compounds formed can differ in volatility as well as in ease of 

ionization.

Spectral interference occurs when the monochromator fails to 

resolve closely spaced resonant frequencies. This type of interference 

is less common in atomic-absorption spectroscopy than in flame 

emission spectroscopy, but may occur especially when multielement
INTRODUCTION 5

hollow-cathode lamps are used (Jaworowski and Weberling, 1966) or 

when the cathodes of single-element lamps contain certain impurities 

that cause them to behave like multielement lamps. During assembly 

of regular multielement lamps, the manufacturer exercises a great 

deal of care to avoid combinations that cause spectral interference, 

but often fails to remove an impurity in a so-called pure metal used 

as a cathode.

lonization interference is most common with alkali-metal determinations and is infrequently observed with the alkaline earths. The 

ease with which these elements ionize leaves fewer atoms in the 

ground state.

The interference due to molecular and particulate absorption 

is more often observed with aqueous solutions of high salt content 

(Angino and Billings, 1967). Originally David (1961) explained such 

interference by postulating that the particles of salt remaining after 

evaporation of small droplets in the flame actually impeded the incident 

radiation which appeared to the detector like absorbed light. The 

term "light scattering" was used to describe the phenomenon, but 

recently Koirtyohann and Pickett (1966) have shown that many 

such observations of the past are due not to light scattering but to 

molecular absorption, calcium being an outstanding example of a 

molecular absorber.

Illustrations of the interferences caused by these effects, and the 

attempts to nullify them, are described in the literature usually in 

connection with a specific need or problem. For example, Willis (1960a) 

adapted atomic-absorption spectroscopy to the determination of 

calcium in blood serum. He noted the depression of the calcium 

absorption by phosphate and suggested two different techniques to 

inhibit the depression: (1) adding ions such as strontium (II) or 

lanthanum (III) to compete with calcium ions for the phosphate, 

and (2) adding a compound such as the disodium salt of ethylenediaminetetraacetic acid to react with calcium and thus prevent its 

reaction with phosphate.

In another specific application P. B. Adams and W. 0. Passmore 

(quoted by Slavin, 1965) added a buffer solution composed of the tetraammonium salt of ethylenediaminetetraacetic acid and lanthanum 

perchlorate to overcome the depression by aluminum on alkalineearth determinations.

Interferences in atomic-absorption spectroscopy are not limited to 

depressive effects. Infrequently the effect is one of enhancement as 

for example the interference of sodium in the determination of potassium noted in natural waters by Fishman and Downs (1966), in 

brines by Billings (1965), and in serum by Willis (1960b). All these

358-974 69-
6 ATOMIC-ABSORPTION METHODS OF ANALYSIS

authors agree that the enhancement results from the ease of ionization 

of sodium and can be offset by equalizing the sodium content of both 

sample and standard or by the method of additions as used in flame 

photometry.

Despite the disadvantages and the extra steps required to compensate for the different kinds of interference described above, atomicabsorption techniques are comparable in accuracy with the widely 

used colorimetric procedures, as shown by the data in table 1.

TABLE 1. Determination of copper content of soils, in parts per 

million, by colorimetric and atomic-absorption methods

Colorimetry Atomic

Sample (in 1964) absorption

(in 1967)

1_ _ ____ _.__ _

2________ _ _....___...

3__ __ 

4. __________ ... ._.

5__-_---__-----_-------

6 _ .--.._.---__._-._._

7___~ - _----

______.___..__.. 10

__-__...-__..._. 15

__---_.._-.__._. 20

._..___._.._.... 20

..--__._-...____ 30

_..._.. _._... 60

__--_...-._._.._ 150

12

14

20

24

30

68

150

Another advantage of atomic-absorption techniques is the number 

of elements that can be determined from a single solution of a given 

sample, as shown by the data in table 2. All these elements were 

determined from a single dilute nitric acid solution of the ash.

TABLE 2. Atomic-absorption analysis, in parts per million, of fir ash

Sample Copper Lead Bismuth Zinc Silver

1_ ___ . ___ ._

2_________________

3____. ..._. _._....

4____ _.._..__...__

5-_ - __-

6_ .. . ___ _

__- __ 60

-.._......__. 70

..__._.__.... 90

- _ __ 80

............. 70

_-._.._...._. 180

60

40

30

30

30

30

30

40

<20

30

20

20

1,500

2,200

2,800

2,000

1,400

3,600

<">

2

2

<2

<^9

6

The accuracy, speed, and simplicity of the proposed atomicabsorption methods are readily apparent. Moreover, these methods 

are obviously most useful when large numbers of samples need to be 

analyzed for a relatively few elements to establish gross differences in 

composition that can be related to geologic controls and features.

These analytical methods resemble the colorimetric methods used 

in geochemical exploration (Ward and others, 1963) in design objectives such as speed, simplicity, and accuracy commensurate with the 

problem.

The minimum content of elements detectable by each of the methods 

described below and the content detectable by other analytical
INTRODUCTION 7

methods found useful in geochemical exploration are given in table 3, 

together with the average content of the same elements in soils, 

basalts, and granites.

TABLE 3. Minimum concentrations detectable by methods useful in geochemical 

exploration and average contents of the elements in soils, basalts, and granites

IF J

Sensitivity of method

Element

Bismuth _ ______

Calcium________.

Cobalt...-----..

Copper _ _----..

Nickel. _________

(ppm)

Colori- Spectro- Atomic 

metric 1 graphic 1 absorption 2 

d-carc

10

10

10

25

2 ...

25

25

10

20 

10 

5

10

5

1

200

10 

5 

. 2 

4 

. 1 

.005 .

1 

. 5 .

.001 

4 

2 5

1 

2.5 .

. 2 .

. 5

Average content (ppm, except as noted)

Soils 1

4 0.2

.5 

8 

20

30

.01 

40

. 1

50

Basalts 3

0. 15 

5 6. 72 

.2 

48 

100 

.004 

5 

10 

.08 

150 

5 .83 

. 1 

8 1. 94

100

Granites '

0. 18 

5 1.58 

.2 

1 

10 

.004 

20 

30 

.08 

. 5 

5 3. 34 

. 04 

s 2. 77

40

1 From Ward, Lakin, Canney, and others (1963).

2 Present report.

sFromTaylor (1964).

4 Value given in crustal abundance (Mason, 1058).

' Values in percent.

The sensitivities given in table 3 are of concentrations expressed in 

parts per million that produce a positive result with the colorimetric 

methods, a definite line on a photographic film with the spectrographic methods, or a distinguishable signal above background on an 

atomic-absorption instrument.

All the methods described in this report have been adapted to the 

model 303 and some to both models 303 and 290 atomic-absorption 

instruments, which are marketed in the United States by the PerkinElmer Corp. Other instruments manufactured in the United States 

and elsewhere are equally useful, and the fact that the name of an 

instrument is used in this report does not constitute a written or 

implied endorsement of that instrument.

The sensitivity of an atomic-absorption method is defined by most 

workers (for example, Slavin, 1968) as the concentration of the element in solution that produces 1 percent absorption. Our values are 

somewhat greater and are determined as in the following paragraph.

When the readout meter of a model 290 instrument is set for fullscale deflection while atomizing a 10-ppm standard solution, we read 

signals of not less than 2.5 scale divisions which corresponds to a
8 ATOMIC-ABSORPTION METHODS OF ANALYSIS

solution of 0.25 ppm. If the instrument is unsteady we cut off at 5 

scale divisions or 0.5 ppm of element being determined. Infrequently 

the lowest standard differs from the sensitivity given in table 3 

because of particular conditions. In all cases, however, the sensitivities 

given in table 3 and discussed under the individual elements are 

established as above.

We present a general procedure for sample attack with boiJing 

nitric acid when analyzing for silver, bismuth, cadmium, lead, copper, 

zinc, cobalt, and nickel; the specific directions for preparation of 

working standard solutions; instrumental parameters for PerkinElmer atomic-absorption instruments models 303 and 290; and a 

brief discussion of interferences, special precautions, warnings, or 

reasons for certain steps. Initially we relied heavily on the instrumental parameters furnished in the Perkin-Elmer instruction book 

(Perkin-Elmer Corp., 1966) and altered them where necessary to meet 

our needs.

All the determinations described in this report, except those for 

tellurium and mercury, can be made on the model 290 spectrophotometer, and where the procedures described include operating conditions 

for only the model 303, the authors mean simply that the model 290 

has not been used enough for the particular analysis to establish such 

parameters.

Boiling nitric acid is used to effect sample dissolution in eight of 

the procedures given here. The boiling nitric acid is used because it is 

less dangerous than hot perchloric acid, especially under field conditions and in the hands of relatively untrained personnel, and 

because the sample solution of about 7 M nitric acid is less corrosive 

on the metal parts of the burner-nebulizer assembly than aqua regia, 

for example. Moreover, the significant trace amounts of metal in 

exploration have quite likely been introduced into the rocks by 

hydrothermal or other genetic processes, and such metals are easily 

solubilized by boiling nitric acid. Background amounts of metals such 

as copper and zinc in crystal lattices of silicates are less significant in 

exploration, and the need to solubilize them is not as important in 

exploration as in abundance and distribution studies. Few, if any, 

strong geochemical anomalies will be missed because of the use of 

boiling nitric acid for sample dissolution.

We also present a general procedure of sample attack with nitric, 

perchloric, and hydrofluoric acids when analyzing for calcium, lithium, 

potassium, and sodium, followed by specific directions, instrumental 

parameters, and precautions as stated above.

We also include three methods for determining gold, one method 

for tellurium, and a nonsolution-of-sample procedure for determining 

background concentrations of mercury.
GENERAL PROCEDURE 9

Caution. Because of the varied experience of persons who may use 

these procedures, we emphasize that most chemical reagents are 

poisonous and require care in handling, especially around open flames, 

bottles, and the like. Further caution and a complete discussion of 

possible hazards are given by Ward, Lakin, Canney, and others 

(1963, p. 5).

ATOMIC-ABSORPTION DETERMINATION OF THE 

CONSTITUENTS

SILVER, BISMUTH, CADMIUM, LEAD, COPPER, ZINC, COBALT, 

AND NICKEL IN ROCKS AND SOILS

GENERAL PROCEDURE

REAGENTS AND EQUIPMENT

Nitric acid, concentrated, ACS (American Chemical Society).

Water, metal-free, demineralized prepared by passing tap or, preferably, distilled water through a demineralizer cartridge or other 

resin bed. (In this bulletin water always means metal-free or demineralized water.)

Culture tubes, 16- by 150-millimeter, calibrated at 10 milliliters.

Magnets, Teflon-covered, %- by Ke-inch. (Infrequently, the Teflon 

develops holes or becomes porous exposing magnets to hot acid 

attack, resulting in contamination of sample solution.)

Magnetic stirrer and hotplate, fitted with aluminum heating block 

drilled to hold culture tubes.

Centrifuge, desirable but not necessary.

Spectrophotometer, atomic-absorption.

SAMPLE DIGESTION

Place 1.0 gram of powdered rock or soil in a 16- by 150-mm test 

tube. Add one small Teflon-covered magnet and 5 ml concentrated 

nitric acid. Place tube and contents in one hole of an aluminum heating 

block fitted on top of hotplate equipped with magnetic stirrer. Start 

agitation of sample-acid mixture and heat to boil. Continue boiling 

and stirring for 30 minutes. Remove tube from block, allow solution 

to cool slightly, add 5 ml water, heat mixture to boil and then allow to 

cool. Make up to 10-ml mark with concentrated nitric acid. Mix and 

centrifuge or filter.

ESTIMATION

Zero instrument with 1:1 nitric acid and atomize the supernatant 

liquid or filtrate in an atomic-absorption spectrophotometer. Read the
10 ATOMIC-ABSORPTION METHODS OF ANALYSIS

absorbance and convert to concentration in atomized solution as 

directed below for the particular instrument. Calculate results as 

follows:

Ppm in sample=(Atg/ml in solution) X 10.

INSTRUMENT CALIBRATION

Note. The following directions are complementary to the detailed 

directions included in the different instrument manuals, which the 

analyst should study before attempting any atomic-absorption 

determinations.

Model SOS using X 1 scale expansion. Atomize three or more working standard solutions, and manually measure the percent absorption. 

Refer to the conversion table furnished with the instrument to change 

percent absorption to absorbance, and prepare a standard curve by 

plotting concentrations of the working standard solutions against the 

corresponding absorbance values.

If the conversion table is not available, the percentage of absorption 

can be converted to absorbance as follows:

Absorbance ATI i [~i percentage of absorption"! = log I - 7 - 

For example, when percentage of absorption is 42 as measured on 

model 303, then

absorbance= log [1 0.42] = log [0.58] 

= -[-0.237] = 0.237.

If the model 303 is equipped with digital concentration readout 

(DCR), atomize the largest working standard solution and set 

readout at the concentration being atomized as directed in the manual 

for the readout. This accessory performs automatically all the operations shown above for manual operation; and, if the system responds 

linearly not necessarily required but preferable then lesser concentrations can be read out directly.

Model 290. Atomize the largest working standard solution and 

set the meter to maximum deflection usually 100. With linearly 

responding systems the meter deflection is proportional to the concentration of the element being atomized, and direct readout is 

possible, thus avoiding setting up standard curves and the like.

If the sensitivity is inadequate to achieve full-scale deflection with 

the largest working standard solution of the element being determined, set the meter, which on the model 290 is linear with respect 

to absorbance, at some convenient number and use only the part of 

the scale from zero to that number. For example, set the meter at 50 

and use only the part of the scale from 0 to 50.
SILVER 11

SPECIFIC PROCEDURES

SILVER

The atomic-absorption method given here is a modification of one 

described by Huffman, Mensik, and Rader (1966), who reported 

that as little as 1 ppm and as much as 9,000 ppm (about 0.03 to 250 

troy ounces per ton) silver can be determined without preliminary 

separation from high concentrations of such elements as iron, nickel, 

copper, bismuth, arsenic, and antimony.

A greater sensitivity is achieved in the modified procedure described here by taking advantage of the scale expansion provided in 

the model 303 atomic-absorption instrument. As little as 0.02 ppm 

silver can be measured, which in the procedure given here corresponds 

to 0.1 ppm in the soil or rock sample. Such concentration is only an 

order of magnitude greater than the crustal abundance; and if the 

sample size is doubled and other reagents are held constant, a sensitivity of 0.05 ppm is achieved permitting the detection of anomalous 

amounts in the earth's crust.

The silver in the rock or soil sample is dissolved in hot concentrated 

nitric acid stabilized with mercuric nitrate (Rubeska and others, 1967) 

and subsequently diluted with water to decrease the acid concentration 

to about 7 M. The silver content is measured by atomic-absorption 

spectrometry using working standard solutions for instrument calibration and instrumental parameters as given below.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are given below. 

Mercuric nitrate reagent: Dissolve 150 mg mercuric nitrate in 500 ml

concentrated nitric acid.

Standard solutions:

Silver standard Concentration Procedure 

stock solution (ppm)

A................ 1,000 Dissolve p.158 g silver nitrate in 100 ml

1:1 nitric acid. 

B................ 100 Prepare fresh by diluting 10 ml of A to 100

ml with 1:1 nitric acid. 

C................ 50 Prepare fresh by diluting 50 ml of B to 100

ml with 1:1 nitric acid. 

D................ 10 Prepare fresh by diluting 10 ml of B to 100

ml with 1:1 nitric acid. 

E................ 5 Prepare fresh by diluting 50 ml of D to 100

ml with 1:1 nitric acid. 

F................ 0. 5 Prepare fresh by diluting 10 ml of E to 100

ml with 1:1 nitric acid.
12 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Working silver standard solutions (to prepare 50-ml solutions of 1:1 

nitric acid containing indicated concentrations of silver in parts 

per million, dilute 5 ml of the indicated stock solutions to volume 

with. 1:1 nitric acid):

Concentration Stock solution

0.05.----------------------------------------------------- F.

0.5 ---------------------------------------------------- E.

1.0___._-_--_..__---.-_--_----_--------_._--_____..__-_.__ D.

5.O. _-_------------------------------------------__._-- C.

Optimum working range with model 303: 

Manual (X 1), 0.2 through 5.0 ppm.

(X 5), 0.02 through 0.5 ppm. 

DCR, 0.02 through 5.0 ppm. 

Operating conditions for model 303: 

Wavelength, 3280 A. 

Source, hollow cathode. 

Lamp current, 12 ma (milliampere). 

Range, ultraviolet. 

Slit, 4. 

Boling burner:

Air pressure, 30 psi (pounds per square inch). 

Acetylene pressure, 8 psi.

Sample digestion: Place 1 g of powdered rock or soil in a 16- by 150- 

mTn test tube. Add I small Teflon-covered magnet and 5 ml of 

mercuric nitrate reagent. Place tube and contents in the hole of an 

aluminum heating block and continue as in "General procedure"

(P- 9).

Estimation: Refer to "General procedure" (p. 9).

Discussion: After sample dissolution and collection of the silver in 

an acid solution the actual measurement by atomic-absorption 

spectrometry is relatively easy and free of interferences (Slavin, 

1968). H. W. Lakin (oral commun., 1968) observed that traces of 

chloride in the reagents and the water caused precipitation of the 

silver. A similar observation was made by Rubeska, Sulcek, and 

Moldan (1967), who reasoned that mercury would remove the 

interference by forming a less dissociated compound with chloride. 

The procedure given above includes addition of mercury as the 

nitrate.

BISMUTH

The atomic-absorption determination of bismuth in altered rocks 

is discussed in detail by Ward and Nakagawa (1967). Sample dis-
BISMUTH 13

solution with boiling nitric acid is effective on bismuth minerals 

such as bismuthinite and certain associated minerals such as tetradymite and galena. Without any enrichment or preconcentration as 

little as 10 ppm of bismuth is measured with a relative standard 

deviation of about 10 percent. This sensitivity has to be improved to 

detect anomalous amounts of bismuth inasmuch as the crustal abundance is of the order of 0.01-0.1 ppm. Techniques for improving the 

sensitivity are being investigated, but meanwhile the method has 

proved useful in pinpointing areas of possible economic potential.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Bismuth standard Concentration Procedure 

stock solution . (ppm)

A. _______________ 1, 000 Dissolve 0.5 g bismuth metal in 500 ml

concentrated nitric acid. 

B____________ 100 Prepare by diluting 10 ml of A to 100 ml

with 1:1 nitric acid. 

C-_--_._______ 50 Prepare by diluting 50 ml of B to 100 ml

with 1:1 nitric acid. 

D____________ 10 Prepare daily by diluting 10 ml of B to 100

ml with 1:1 nitric acid.

Working bismuth standard solutions (to prepare 50-ml solutions of 

1:1 nitric acid containing indicated concentrations of bismuth in 

parts per million, dilute 5 ml of the indicated stock solutions to 

volume with 1:1 nitric acid):

Concentration Stock solution

l..._......._....__.. ............_ . ...... D.

5 _ - _ -_ - _-_ -_ C.

10_-____-___-___-__--______-___.______--_--_-_-_---__--__ B.

Optimum working range with model 303:

Manual (X 1), 1 through 10 ppm.

DOR, 1.0 through 10 ppm. 

Operating conditions for instruments:

Model SOS Model 200

Wavelength (counter) _____ _ ___ 2230 A 98. 5

Source__-__--___-___-__-___--_-___- Hollow cathode Hollow cathode

Lamp current._____________.___ma__ 30 12

Slit_--__-_______--_-_______-_._-___ 3 7 A

Boling burner:

Air pressure-__-_------__-__psi-- 30 30

Acetylene pressure._________psi__ 8 8

358-974 69 3
14 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Sample digestion: Refer to "General procedure" (p. 9).

Estimation: Refer to "General procedure" (p. 9).

Discussion: Billings (1965) reported that "calcium interferes strongly" 

with bismuth; although we have not observed such interference 

with rocks and soils, we confirmed his report during the analysis 

of samples of alfalfa collected in Arizona and Utah. The air-dried 

alfalfa was ignited at 450° C overnight and the resulting ash was 

leached with boiling nitric acid. The acid solution of each sample 

was atomized into a flame, and the absorption of the 2230-angstrom 

bismuth line in the presence of about 15,000 ppm calcium corresponded to about 70-80 ppm bismuth in the ash. The ash contains 

less than 10 ppm bismuth when analyzed by a colorimetric 

procedure.

CADMIUM

The atomic-absorption determination of cadmium in rocks and 

soils is discussed in detail by Nakagawa and Harms (1968). Without 

any preconcentration as little as 0.2 ppm of cadmium in a soil or rock 

is measured with reasonable precision. The crustal abundance of 

cadmium is of the same order of magnitude and thus any anomalous 

amount in a rock is detectable by the procedure.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Cadmium standard

stock solution

A.... ............

B....... .... .....

C... .............

D................

E... .............

F.......... ......

Concentration (ppm)

. 1, 000

100

10

1

0.5

0.2

Procedure

Dissolve 0.1142 g cadmium oxide in 100 ml

1: 1 nitric acid. 

Prepare by diluting 10 ml of A to 100 ml

with 1 : 1 nitric acid. 

Prepare by diluting 10 ml of B to 100 ml

with 1 : 1 nitric acid. 

Prepare daily by diluting 10 ml of Cto 100 ml

with 1 : 1 nitric acid. 

Prepare daily by diluting 50 ml of D to 100

ml with 1 : 1 nitric acid. 

Prepare daily by diluting 20 ml of D to 100

ml with 1 : 1 nitric acid.

Working cadmium standard solutions (to prepare 50-ml solutions 

of 1:1 nitric acid containing indicated concentrations of cadmium
LEAD 15

in parts per million, dilute the indicated stock solutions to volume 

with 1:1 nitric acid):

Concentration Stock solution

0.02....._______________________________________ 5 ml of F.

0.05- -.._-._.-._.__-___---_-_-_-_--_----__ 5 ml of E.

1.0_____________________________________________ Use D above.

3.0 _-----_---_------__--__-----_------------_ 15 ml of C.

Optimum working range with model 303:

Manual, 0.02 through 1 ppm or 0.5 through 3 ppm. 

DOR, 0.02 through 3 ppm.

Operating conditions for instruments:

Model SOS Model 290

Wavelength (counter) ____. _____ 2288 A 109

Source. ____________________________ Hollow cathode Hollow cathode

Lamp current.._----__-----_--.ma... 6 3

Slit--__----___..._.._-..-_.-_---.-. 4 7 A

Boling burner:

Air pressure.______-__--.-__psi-_ 30 30

Acetylene pressure._________psi__ 8 8

Sample digestion: Refer to "General procedure" (p. 9).

Estimation: Refer to "General procedure" (p. 9).

Discussion: The method has been successfully used to determine 

trace amounts of cadmium in zincite, sphalerite, and oxidized ores 

with no observed interference. The selectivity and sensitivity are 

adequate for the analysis of cadmium in geologic materials, and 

thus, this method can relieve the scarcity of data heretofore caused 

by the lack of a selective analytical procedure.

LEAD

The emission from the older lead hollow-cathode lamps used in 

most commercial atomic-absorption instruments was low because the 

discharge occurred on the outside and the inside of the hollow cathode. 

The discharge on the outside contributed little to the emitted energy 

which originated primarily in the cathode cavity (Manning and 

Vollmer, 1967). Accordingly, the relative detection limit achieved for 

lead was much less than that for zinc or copper. Despite this drawback, 

atomic-absorption techniques have been widely used on a variety of 

geologic and metallurgical materials.

The new shielded lamps have an insulating shield positioned around 

the cathode so as to restrict the discharge to the cathode cavity and 

thereby to increase the emitted energy at a given lamp current. The 

increased emission results in greater sensitivity, other factors being 

equal.
16 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Background amounts of lead in rocks and soils are of the order of 

15-20 ppm, and the procedure given here with a sensitivity of 0.1 ppm 

is more than adequate to measure such amounts. In fact the good 

sensitivity and relatively high background allow one to dilute the 

sample solution appreciably to achieve a uniform matrix and to 

nullify possible interferences.

The accuracy of the lead determinations in the different rocks is 

established by comparing lead contents determined by the proposed 

atomic-absorption method with lead contents determined by independent methods such as colorimetry and emission spectrography. 

The data for such a comparison are shown in table 4.

TABLE 4. Lead content, in parts per million, of rocks and minerals

Sample Material Atomic Colorimetry 2 Spectrogabsorption > raphy 3

R4A__._

7A

5A

3A

8A

6A

_ _ Hornblende______ ______ __

___ Basalt _ ____ _______ __

___ Biotite _ _________________

_ Granite. ___ __ ____ _____

13

14

14

17

19

22

23

7

10

16

20

24

13

35

<10

<10

10

20

20

20

' Average of five determinations by procedure described in this report.

a Average of 10 colorimetric measurements after sample digestion with HF-HC1O4-HNO3.

8 Semiquantitative three-step procedure.

The agreement of values obtained by the three independent methods 

is ample evidence of the accuracy of the proposed method.

The repeatability of the atomic-absorption method is established by 

several separate determinations on different kinds of rocks. The 

highest and lowest values obtained for lead in several rock and mineral 

samples, as well as the confidence limits at the 95-percent level and 

the relative standard deviations, are shown in table 5.

TABLE 5. Repeatability of lead determinations on rocks and minerals 

[Average of five determinations]

Lead (ppm)

Sample Material

R4A_______ Hornblende- __ ______

2A_______ Sandstone ___________

7A_______ Basalt.- _____________

3A_______ Biotite.---.-- _______

6A_______ Granite. _____________

Low

_.__ 10

--_. 12

____ 12

14

_-__ 18

--.- 20

____ 22

High

16 

16 

16 

18 

20 

24 

24

Mean and 

confidence 

limits at 

95-percent 

level

13. 2±2. 9 

13. 6±2. 1 

14. 0± 1. 8 

16. 8±2. 2 

19. 2± 1. 4 

22. 4±2. 1 

22.8+1.4

Relative 

standard 

deviation 

(percent)

17.4 

12.5 

10. 0 

10.7 

5.7 

7.6 

4.8
COPPER 17 

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Lead standard stock Concentration Procedure 

solution (ppm)

A__________ 1,000 Dissolve 1.6 g lead nitrate in 1,000 ml of

1:1 nitric acid. 

B____________ 100 Prepare by diluting 10 ml of .4 to 100 ml with

1:1 nitric acid. 

C_.______ 10 Prepare daily by diluting 10 ml of B to 100

ml with 1:1 nitric acid.

Working lead standard solutions (to prepare 50-ml solutions of 1:1 

nitric acid containing indicated concentrations of lead in parts per 

million, dilute the indicated stock solutions to volume with 1:1 

nitric acid):

Concentration Stock solution

2______________________._______________________ 10 ml of C.

10___----______________________________________ Use C above.

30 ___ _ _._ _ _ _ 15 ml of B.

Optimum working range with model 303:

Manual (X 1), 1 through 30 ppm. 

(X 5), 0.1 thro ugh 3 ppm.

DOR, 0.1 through 10 ppm. 

Operating conditions for instruments:

Model SOS Model 290

Wavelength (counter)___________ 2170 A 205

Source-____________________________ Hollow cathode Hollow cathode

Lamp current-_________________ma__ 30 15

Slit 4 7 A

Boling burner:

Air pressure________________psL. 30 30

Acetylene pressure._-_---_-_psi__ 8 8

Sample digestion: Refer to "General procedure" (p. 9). 

Estimation: Refer to "General procedure" (p. 9).

COPPER

Copper is perhaps the easiest of all the metals to determine by 

atomic-absorption spectrometry, and the simplicity of the measurement as well as the freedom from interferences prompted Slavin 

(1968) to observe that it is most often used to check instrument 

performance. Instrumental changes do little "to degrade the copper
18 ATOMIC-ABSORPTION METHODS OF ANALYSIS

analysis." Further evidence of its ease of determination is provided 

by the success of Belt (1964) in copper determinations in complex 

geologic materials and of Strasheim, Strelow, and Butler (1960) in 

ores.

The crustal abundance of copper is of the order of 10-20 ppm and 

the method described here has a sensitivity of about 0.1 ppm more 

than enough to determine background amounts and anomalous 

concentrations.

The copper of exploration significance found in rocks and soils is 

due mostly to weathered products of primary minerals and is readily 

soluble in hot nitric acid. The effectiveness of such a treatment on a 

suite of rocks and minerals and a measure of the accuracy achieved 

are shown by comparing the copper contents obtained by the atomicabsorption procedure with those obtained by established procedures 

colorimetry (Ward and others, 1963) and semiquantitative spectrography (Myers and others, 1961). The results are given in table 6.

TABLE 6. Copper content, in parts per million, of rocks and minerals

Sample Material Atomic Colorimetry 3 Spectrogabsorption l raphy 3

R6A..._

2A____

8A-_._

5A.._.

4A____

3A____

7A____

___ Granite. _______ ___. __.

___ Sandstone... ____________

_ _ Dolomite......... _______

... Biotite. __________________

___ Basalt. ____________ _____

.... 2.4

.... 3.9

--.. 6.4

.... 6.8

..... 37

..___ 40

__._ 57

4

6

6

8

31

38

50

5

20

5

10

50

50

50

1 Average of five determinations by procedure described in this report.

8 Average of 10 colorimetric measurements after sample digestion with HF-HC104-HN03.

«Semiquantitative three-step procedure.

The good agreement of the results obtained by the different 

analytical techniques on such a wide variety of rocks and minerals 

is ample evidence of the accuracy of the atomic-absorption method.

The repeatability of the atomic-absorption procedure was established by making five separate determinations of the copper content 

of the suite of rocks and minerals (table 6). The lowest and highest 

values obtained, as well as the confidence limits at the 95-percent 

level and the relative standard deviation, are shown in table 7.

The relative standard deviation for rocks containing about 6 ppm 

copper is approximately 10 percent, which compares favorably with 

that reported by Belt (1964) for similar copper concentrations in a 

granite.
COPPER

TABLE 7. Repeatability of copper determinations on rocks and minerals 

[Average of five determinations]

19

Sample Material

R6A_ ______ Granite. -_-----_-_-_.

4A_______ Hornblende _________

3A_______ Biotite.______--__-___

Copper (ppm)

Low

.___. 2.0

.___. 3.6

.____ 6.0

_.__ 6.0

____ 36.0

___. 39. 0

____ 57.0

High

2.8 

4.4 

7. 2 

7.6 

38.0 

41. 0 

58.0

Mean and 

confidence 

limits at 

95-percent 

level

2. 4±0. 7 

3. 9±0. 4 

6. 4±0. 8 

6. 8±0. 9 

37. 4± 1. 0 

40. 3±1. 7 

57. 2±0. 4

Relative 

standard 

deviation 

(percent)

19 

9 

10 

11 

2.1 

3.3 

0.6

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Copper standard 

stock solution

Concentration 

(ppm)

Procedure

B.

100 Dissolve 0.1964 g of clear uneffloresced 

crystals of copper sulfate (CuSCVSH^O) 

in 500 ml of 1:1 nitric acid. 

10 Prepare daily by diluting 10 ml of A to 100

ml with 1:1 nitric acid.

1 Prepare daily by diluting 10 ml of B to 100 

ml with 1:1 nitric acid.

Working copper standard solutions (to prepare 50-ml solutions of 

1:1 nitric acid containing indicated concentrations of copper in 

parts per million, dilute the indicated stock solutions to volume 

with 1:1 nitric acid):

Concentration Stock solution

0.2. 10 ml of C. 

Use C above. 

10 ml of B. 

25 ml of B.

Optimum working range with model 303: 

Manual (XI), 0.5 through 10 ppm. 

(X 5), 0.05 through 1 ppm. 

DOR, 0.01 through 5.0.
20 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Operating conditions for instruments:

Model SOS Model 890

Wavelength (counter)__________ 3248 A 280

Source____________-___-________---_ Hollow cathode Hollow cathode

Lamp current__________________ma__ 15 5

Slit _. _.._-_------__.--. 4 7 A

10-cm burner:

Air pressure______________-_psi_- 30 30

Acetylene pressure__________psi-_ 8 8

Sample digestion: Refer to "General procedure" (p. 9). 

Estimation: Refer to "General procedure" (p. 9).

ZING

The determination of zinc by atomic-absorption spectroscopy 

appears easy at first glance. The crustal abundance is of the order of 

100 ppm and with a sensitivity of 0.5 ppm one can make several-fold 

dilutions of sample solution and thereby nullify possible matrix and 

spectral interferences.

The accuracy of zinc determinations on different kinds of rocks is 

established by comparing the results obtained by the proposed atomicabsorption method with those obtained by other tested methods referred to above. The data are shown in table 8.

TABLE 8. Zinc content, in parts per million, of rocks and minerals 

[__., not determined]

Sample Material Colorimetry' Atomic Atomic

absorption 2 absorption 3

R2A-...

8A_ 

5A 

4A____

3A____

6A____

7A__._

___ Sandstone. ____ ___________

-.. Hornblende __ __________

.__ Biotite_____- ________ __

___ Basalt __________________

_--_ 11

____ 17

-___ 75

100

---_ 100

._-_ 100

.___ 120

4.4 ___

11. 1

49.5 _._

20

164 ___

128

32

23

85

80

120

 Average of 10 or more colorimetric measurements after sample digestion with HF-HC104-HN03.

2 Average of five determinations by procedure described in this report.

» Single determination by atomic absorption after sample digestion with HF-HNO 3.

The digestion of the samples with hot concentrated nitric acid is 

adequate for solubilizing trace amounts of zinc in many rock types, 

but remarkably inadequate for rocks in which the metal is possibly 

bound in a silicate lattice such as in a rock containing hornblende. In 

fact, most atomic-absorption procedures for determining zinc in geologic materials call for the use of a mixture of hydrofluoric acid and 

some other acid to insure breakdown of the silicates. However, the 

fact that the simpler digestion with boiling nitric acid is effective in 

revealing the presence of anomalous amounts of zinc warrants its 

continued use in place of the more drastic treatment involving hydrofluoric acid.
ZINC 21

The repeatability of the proposed method is shown by the data in 

table 9. The repeatability of the zinc determinations on rocks such as 

the quartz monzonite as measured by the relative standard deviation 

is comparable to that observed by Belt (1967) for similar rocks. It is 

not good, possibly due to incomplete solution, but is deemed adequate 

for geochemical exploration.

TABLE 9. Repeatability of zinc determinations on rocks and minerals 

[Average of five determinations]

Sample

R2A___.

4A

7A.__.

6A

3A

Material

___ Sandstone. _ _______

___ Dolomite.-- _ ______

___ Hornblende __

Basalt _ _

___ Quartz monzonite. ...

Zinc (ppm)

Low

___ 3. 6

 10. 4

_ 18. 4

___ 29. 8

___ 47. 2

___ 116. 0

... 126.0

High

6.4 

11.8 

20.8 

33.8 

50.2 

164.0 

246.0

Mean and 

confidence 

limits at 

95-percent 

level

4. 4± 1.4 

11. 1± 0. 6 

20. 0± 1. 4 

32. 2± 2.0 

49. 5± 2. 1 

128. 0±31. 0 

164. 0±62. 0

Relative 

standard 

deviation 

(percent)

25.0 

4.5 

5.5 

4.9 

3.4 

19.3 

30. 2

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Zinc standard stock Concentration 

solution (ppm)

Procedure

A_______________ 1,000

B .-.._______ 100

C _____________ 10

D..... ___________ 1

E................

Dissolve 1 g zinc metal in 1 liter of 1:1 nitric

acid. 

Prepare by diluting 10 ml of A to 100 ml

with 1:1 nitric acid. 

Prepare daily by diluting 10 ml of B to 100

ml with 1:1 nitric acid. 

Prepare daily by diluting 10 ml of C to 100

ml with 1:1 nitric acid. 

0. 5 Prepare daily by diluting 50 ml of D to 100

ml with 1:1 nitric acid.

Working zinc standard solutions (to prepare 50-ml solutions of 1:1 

nitric acid containing indicated concentrations of zinc in parts per 

million, dilute the indicated stock solutions to volume with 1:1 

nitric acid): x

Concentration Stock solution

0.05. 

0.1-- 

0.2__ 

1_.

5 ml of E. 

5 ml of D. 

10 ml of D. 

Use D above. 

15 ml of C.

358-974 6£
22 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Optimum working range with model 303: 

Manual (XI), 0.2 through 3.0 ppm. 

(X 5), 0.05 through 0.2 ppm. 

DCR, 0.05 through 3.0 ppm. 

Operating conditions for model 303: 

Wavelength, 2138 A. 

Source, hollow cathode. 

Lamp current, 15 ma. 

Slit, 4. 

Boling burner:

Air pressure, 30 psi. 

Acetylene pressure, 8 psi.

Sample digestion: Refer to "General procedure" (p. 9). 

Estimation: Refer to "General procedure" (p. 9). 

Discussion: A detailed study by Ward and Nakagawa (1969) confirmed several kinds of interference such as the effect of acid concentration noted by Gidley and Jones (1960) and the effect of 

sodium, potassium, magnesium, and iron noted by Billings (1965). 

These effects are in addition to the problem of sample dissolution 

discussed above.

COBALT

The following procedure is simple and useful in determining the 

small amount of easily dissolved cobalt in soils and rocks. The practical 

sensitivity of the procedure is of the order of 2-4 ppm depending on 

the size of the sample used. Such sensitivity is enough to measure 

background amounts ranging from 1 to 50 ppm and more than adequate 

to detect anomalous amounts.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Cobalt standard Concentration Procedure 

stock solution (ppm)

A................ 1,000 Dissolve 1.97 g cobalt chloride (CoCl2 -6H2O)

in 500 ml of 1:1 nitric acid. 

B................ 100 Prepare by diluting 10 ml of A to 100 ml

with 1:1 nitric acid. 

C................ 10 Prepare daily by diluting 10 ml of B to 100

ml with 1:1 nitric acid. 

D....-_--_ ____ 5 Prepare daily by diluting 50 ml of C to 100

ml with 1:1 nitric acid. 

E................ 1 Prepare daily by diluting 10 ml of C to 100

ml with 1:1 nitric acid.
NICKEL 23

Working cobalt standard solutions (to prepare 50-ml solutions of 1:1 

nitric acid containing indicated concentrations of cobalt in parts 

per million, dilute the indicated stock solutions to volume with 1:1 

nitric acid):

Concentration Stock solution

0.2__.________..--.....__._...___.....__.._ 10 ml Of E.

0.5-. --.-._---------___-____--------_ 5 ml of D.

!______________________________________________ Use E above.

3__-----.--__--_-_-_.--____---__...___ 15 ml of C.

5_-__---___--______-__-___--___--___________- Use D above.

Optimum working range with model 303:

Manual (XI), 0.2 through 5 ppm.

DCR, 0.2 through 5 ppm. 

Operating conditions for instruments.

Model SOS Model £90

Wavelength (counter)__________ 2407 A 131.5

Source--_-_----_---_____-________ Hollow cathode Hollow cathode

Lamp current__-___-_--__-__-ma__-- 30 10

Slit..----------._-----.------.-___- 3 2 A

Boling burner:

Air pressure___-__--_.____psi---- 30 30

Acetylene pressure ________ psi_ _ _ - 8 8

Sample digestion: Place 0.5 g of powdered rock or soil in a 16- by 

150-mm test tube and proceed as in "General procedure" (p. 9).

Estimation: Refer to "General procedure" (p. 9).

Discussion: In silicate rocks the atomic-absorption determination of 

cobalt is generally free of interferences (Billings, 1963; Billings 

and Adams, 1964), but in carbonates the determination is affected 

by molecular absorption of the dissolved calcium (Angino and 

Billings, 1967, p. 44). The determination in both silicates and 

carbonates presented no special difficulties for MontagutBuscas, Obiols, and Rodriquez (1967). However, several published 

procedures include lengthy and perhaps tedious separation and 

concentration steps prior to atomizing a cobalt solution in an 

atomic-absorption instrument; therefore, the generalized statements 

above may in fact have only limited support.

NICKEL

The atomic-absorption determination of nickel is relatively easy, 

although a monochromator with a narrow spectral slit width, about 

2 A, is needed to take advantage of the most sensitive resonant line 

at 2320 A. The practical sensitivity of the method included here is 

similar to that of cobalt, 2-4 ppm, and is adequate to measure the 

background amount which for the most part is slightly greater than
24 ATOMIC-ABSORPTION METHODS OP ANALYSIS

the 1- to 50-ppm range given for cobalt (p. 22). Certainly the sensitivity is more than necessary to detect anomalous amounts.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 9) are tabulated below.

Standard solutions:

Nickel standard stock 

solution

A........ ........

B _______ ---____.

C - ... ... _.

D ...... ...... _ .

#-_____.. .......

Concentration 

(ppm)

1, 000

100

10

5

1

Procedure

Dissolve 2.48 g nickel nitrate [Ni(N08)2.

6H2O] in 500 ml of 1 : 1 nitric acid. 

Prepare by diluting 10 ml of A to 100

ml with 1 : 1 nitric acid. 

Prepare daily by diluting 10 ml of B to 100

ml with 1:1 nitric acid. 

Prepare daily by diluting 50 ml of C to

100 ml with 1:1 nitric acid. 

Prepare daily by diluting 10 ml of C to 100

ml with 1:1 nitric acid.

Working nickel standard solutions (to prepare 50-ml solutions of 

1:1 nitric acid containing indicated concentrations of nickel in 

parts per million, dilute the indicated stock solutions to volume 

with 1:1 nitric acid):

Concentration Stock solution

0.2________________________ . _____ 10 ml of E, 

0.5__...____._.___ ..__________ 5 ml of D. 

1________- _________ _._ Use E above.

3...._._...__.. . . . ........... 15 ml of C.

5 . _____ _______________ Use D above.

Optimum working range with model 303: 

Manual (X 1), 0.2 through 5.0 ppm. 

DCR, 0.2 through 5.0 ppm.

Operating conditions for instruments:

Model SOS Model 890

Wavelength (counter)____._____ 2320 A 112. 5

Source_________________.._._____ Hollow cathode Hollow cathode

Lamp current.______ ma__ 25 10

Slit.____-_______________ 3 2A

Boling burner:

Air pressure.__ _._ psi__ 30 30

Acetylene pressure. _ __psi._ 8 8

Sample digestion: Place 0.5 g of powdered rock or soil in a 16- by

150-mm test tube and proceed as in "General procedure" (p. 9). 

Estimation: Refer to "General procedure" (p. 9).
GENERAL PROCEDURE 25

Discussion: The atomic-absorption determination of nickel in silicate 

rocks is relatively free of interferences provided the iron and calcium 

contents are not too great (Billings and Adams, 1964; Ragland and 

Billings, 1965). Molecular absorption by calcium on the nickel line 

at 2320 A is reported by Billings (1965). A correction can be made 

on the line at 2325.7 A. P. C. Ragland (cited in Angino and Billings, 1967) observed molecular absorption by iron and calcium on 

the nickel line during the analysis of granites. As much as 1,000 

ppm of several anions such as sulfate, chloride, phosphate, and 

nitrate and cations such as zinc and lead did not interfere with 

the determination of 1 ppm nickel in water samples (Platte and 

Marcy, 1965).

GENERAL PROCEDURE

REAGENTS AND EQUIPMENT

Dish, 30 ml, platinum or Teflon. 

Flasks, volumetric, 25 ml and 50 ml. 

Hydrochloric acid, 6 M. 

Hydrofluoric acid, 48 percent. 

Nitric acid, concentrated. 

Perchloric acid, 72 percent.

SAMPLE DIGESTION

Place 0.1 g of powdered rock or soil in 30-ml platinum or Teflon dish 

and wet sample with 2 ml concentrated nitric acid, 2 ml perchloric 

acid, and 15 ml hydrofluoric acid. Heat dish gently on hotplate and 

allow contents to evaporate slowly until dry. Cool dish, add 2 ml 

6 M hydrochloric acid and heat gently on hotplate to solubilize 

the residue. Transfer the solution to volumetric flasks as directed 

under the given procedure.

ESTIMATION

Atomize the aqueous solution in an atomic-absorption spectrophotometer. Read absorbance and refer to standard curves prepared 

by atomizing portions of working standard solutions to convert to 

concentration.

INSTRUMENT CALIBRATION

See page 10.
26 ATOMIC-ABSORPTION METHODS OF ANALYSIS 

SPECIFIC PROCEDURES

CALCIUM IN ROCKS AND SOILS

The atomic-absorption determination of calcium is relatively easy 

as shown by the volume of literature describing applications of 

calcium determinations to a wide variety of materials including 

geologic. The early studies of Willis (1960a, 1961) on calcium determination in blood serum, urine, and other materials are typical of 

applications in the clinical laboratory. Calcium determinations in 

soils and plants by atomic-absorption techniques are described by 

David (1959) and Dickson and Johnson (1966).

The calcium abundance in rocks and soils is of the order of 0.5-1 

percent or more, and the following procedure is designed to detect 

the lower limit as well as to measure anomalous concentrations. 

Detection of the lower limit is not a problem because of the good 

sensitivity of the calcium measurement, 0.8 Mg/ml (micrograms per 

milliliter) for 1 percent absorption. Such sensitivity allows considerable latitude in sample dilution to adjust the calcium content to a 

convenient level for measurement.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 25) are given below. 

Dilution reagent: Mix 90 ml water, 10 ml lanthanum chloride reagent,

and 2 ml of 6 M hydrochloric acid.

Lanthanum chloride solution: Weigh 58.7 g lanthanum oxide (La2O3) 

into a 100-ml beaker and wet powder with metal-free water. In 

small portions add 150 ml concentrated hydrochloric acid. When 

the oxide is completely dissolved, dilute to 500 ml with metal-free 

water. Dilute slowly with the water while stirring vigorously to 

avoid overheating.

Standard solutions:

Calcium standard Concentration Procedure 

stock solution (ppm)

A______________ 1, 000 Dissolve 2.485 g dried calcium carbonate

(overnight at 100° C) in mixture of 40 ml 

metal-free water and 40 ml 6 M hydrochloric acid. Dilute to 1 liter with metalfree water.

B................ 500 Prepare by diluting 50 ml of A to 100 ml with

dilution reagent.

C__________ 200 Prepare by diluting 40 ml of B to 100 ml with

dilution reagent.

D................ 100 Prepare by diluting 20 ml of B to 100 ml with

dilution reagent.
CALCIUM IN ROCKS AND SOILS 27

Working calcium standard solutions (to prepare 50-ml solutions of 

dilution reagent containing indicated concentrations of calcium in 

parts per million, dilute the indicated stock solutions to volume 

with dilution reagent):

Concentration Stock solution

10__--..--.--.---_----------------.-.---.------ 5 ml of D.

40._____ _ ____________ . ___________ 10 ml of C. 

60-__-...-.-__-.-.-------------------_------.-- 6 ml of B.

SO-.--------.--------------------...----------- 8 ml of B.

100___----___-_-__..--_.__---__------ UseD above.

200-.---__.___---._-------_-.________ Use Cabove.

Operating conditions for model 290: 

5-cm short-path burner: 

Air pressure, 30 psi. 

Acetylene pressure, 8 psi. 

Burner position:

For 0- to 100-ppm and 0- to 200-ppm scales, position

burner perpendicular to source beam. 

For 0- to 10-ppm scale, position burner in line with

source beam. 

Counter, 460. 

Source current, 8 ma. 

Slit, 7 A.

Sample digestion: Refer to "General procedure" (p. 25). To the 

2 ml of warm hydrochloric acid solution add 5 ml of lanthanum 

chloride solution and transfer to a 50-ml volumetric flask. Make up 

to volume with water and mix.

Estimation: Refer to "General procedure" (p. 25).

Discussion: Although calcium is readily determined by atomic-absorption spectrophotometry, the kinds of interference are more 

numerous and the degree of interference is greater than for most 

other elements. The interferences encountered especially when analyzing plants and soils are discussed in detail by Dickson and 

Johnson (1966). They used protective agents such as strontium 

chloride or lanthanum chloride to nullify the depression of calcium 

absorption caused by anions such as silicate, phosphate, and sulfate. 

The standard additions techniques used so successfully in flame 

emission methods are useful also in atomic-absorption procedures 

when used in conjunction with protective agents like strontium 

nitrate (Dickson and Johnson, 1966) to determine calcium in 

presence of high levels of sulfate and phosphate.
28 ATOMIC-ABSORPTION METHODS OF ANALYSIS

The proposed procedure uses lanthanum chloride to inhibit the 

interference due to phosphate, sulfate, silicate, and cations such as 

aluminum. The chloride concentration in the sample solution is 

reduced to about 0.2 M roughly 700 ppm and this concentration is below the 1,000 ppm stated by Platte and Marcy (1965) 

that did not interfere with measurement of 1 ppm calcium in 

water samples.

CALCIUM IN PLANT ASH

PROCEDURE

Special reagents and equipment, in addition to those listed under 

"General procedure" (p. 25) and under "Calcium in rocks and soils" 

(p. 26), are given below. 

Flasks, volumetric, 100 ml. 

Calcium working standard solutions: See table under "Calcium in

rocks and soils" (p. 26). 

Sample digestion: Weigh 0.05 g plant ash into 100-ml volumetric

flask and add 4 ml 6 M hydrochloric acid. Heat on steam bath 20

minutes, remove and add 10 ml lanthanum chloride solution.

Dilute to volume with metal-free water and mix. 

Estimation: Kefer to "General procedure" (p. 25).

LITHIUM IN ROCKS AND SOILS

The abundance of lithium in rocks and soils is of the order of 20- 

40 ppm, and the sensitivity of about 0.07 ppm for 1-percent absorption achieved under general conditions is more than adequate to 

detect anomalous concentrations in such materials. With scale expansion one can attain an adequate sensitivity to provide greater latitude 

in sample dilution.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 25) are given below.

Dilution reagent: Add 20 ml concentrated hydrochloric acid to 1 liter 

of metal-free water.
LITHIUM IN ROCKS AND SOILS 29

Standard solutions:

Lithium standard 

stock solution

A.... .......... _

B..... ......... ..

C.... ...........

D...... .........

Concentration (ppm)

1, 000

100

10

1

Procedure

Dissolve 6.11 g lithium chloride in mixture

of 1,000 ml metal-free water and 20 ml 

concentrated hydrochloric acid. 

Prepare by diluting 10 ml of A to 100 ml

with dilution reagent. 

Prepare daily by diluting 10 ml of B to 100

ml with dilution reagent. 

Prepare daily by diluting 10 ml of C to 100

ml with dilution reagent.

Working lithium standard solutions (to prepare 50-ml solutions of 

dilution reagent containing indicated concentrations of lithium in 

parts per million, dilute the indicated stock solutions to volume 

with dilution reagent):

Concentration Stock solution

0.5- ._._.--__-__--._________._____._ 25 ml of D.

l__--_-_-_------_--_-_______________-----__-__ 5 ml of C.

2...__________________________________________ 10 ml of C.

10-------_--_-------_-_----_-___-_-__-_---.__-_ 5 ml of B.

Operating conditions for model 290: 

5-cm short-path burner: 

Air pressure, 30 psi. 

Acetylene pressure, 8 psi. 

Counter, 953. 

Source, hollow cathode. 

Lamp current, 5 ma. 

Slit; 7 A.

Sample digestion: Place 0.2 g of powdered soil or rock in 30-ml 

platinum or Teflon dish and proceed as in the "General procedure" 

(p. 25). After treatment, transfer the 2-ml of warm hydrochloric acid solution to a 25-ml volumetric flask, make up to volume 

with water, and mix. 

Estimation: Refer to "General procedure" (p. 25).
30 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Discussion: Controversy exists regarding possible interferences, especially from sodium and potassium. Zettner, Rafferty, and Jarecki 

(1968) reported as much as 9-percent enhancement of lithium 

absorption in solutions containing 50-100 times as much sodium or 

potassium. Slavin and Slavin (1968) found no more than 3-percent 

enhancement from solutions containing 250 times as much sodium 

as lithium. We observed that sodium concentrations of as much as 

1,000 ppm caused about 3-percent deflection of meter on a PerkinElmer model 290 instrument previously calibrated for 100-percent 

deflection by 3 ppm lithium solution. Fishman and Downs (1966) 

reported that more than 5 ppm strontium interfered, but Angino 

and Billings (1966) were unable to confirm this.

POTASSIUM IN ROCKS AND SOILS

The potassium abundance in soils and rocks is of the order of 1-4 

percent and more. The sensitivity of the method described below is 

about 1 ppm, which is more than needed to measure background 

concentrations and enough to require several-fold dilution of the 

sample before measurement of anomalous concentrations.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 25) are given below.

Dilution reagent: Add 20 ml concentrated hydrochloric acid to 1 liter 

of metal-free water.

Standard solutions:

Potassium standard Concentration Procedure 

stock solution (ppm)

A.... ___---__---. 1,000 Dissolve 1.92 g potassium chloride in 1,000

ml of dilution reagent. 

B................ 500 Prepare by diluting 50 ml of A to 100 ml

with dilution reagent. 

C._________ 200 Prepare by diluting 40 ml of B to 100 ml

with dilution reagent. 

D................ 100 Prepare by diluting 10 ml of A to 100 ml

with dilution reagent. 

E................ 10 Prepare daily by diluting 10 ml of D to 100

ml with dilution reagent.

Working potassium standard solutions (to prepare 50-ml solutions of 

dilution reagent containing indicated concentrations of potassium
SODIUM IN ROCKS AND SOILS 31

in parts per million, dilute the indicated stock solutions to volume 

with dilution reagent):

Concentration Stock solution

10.-.. . ___---_ -..._._____.-__-...-._ Use E above. 

20_______________________._______ 10 ml of D. 

40______________________._._____ 10ml of C. 

SO..........--.--_-_.-..--..__._..-..-..--...-. 8 ml of B.

Operating conditions for model 290: 

5-cm short-path burner: 

Air pressure, 30 psi. 

Acetylene pressure, 8 psi. 

Burner position:

For 0-10 ppm, burner in line with source beam. 

For 0-80 ppm, burner perpendicular to source beam. 

Counter, 1169. 

Source, hollow cathode. 

Lamp current, 10 ma. 

Slit, 20 A.

Sample digestion: Refer to "General procedure" (p. 25). After 

treatment transfer the 2 ml of warm hydrochloric acid solution to a 

50-ml volumetric flask, make up to volume with water and mix. 

Estimation: Refer to "General procedure" (p. 25). 

Discussion: The atomic-absorption determination of potassium is 

limited by spectral interference from sodium, as noted by Fishman 

and Downs (1966), Wfflis (1960b), and Trent and Slavin (1964). 

The interference is due to ionization and is nullified by equalizing 

the sodium content of standards and samples (Billings and Harriss 

1965). For determining potassium in water, Fishman and Downs 

(1966) provided easy guidelines to match standards with samples. 

They found that in samples that contain as much as 1,000 ppm of 

sodium the effect of the sodium ion on the potassium measurement 

was constant over a range of ± 50 ppm, and accordingly they added 

200 ppm sodium to each standard and then adjusted the sample 

solution until the sodium ion concentration fell into the range of 

150-250 ppm prior to the measurement.

SODIUM IN ROCKS AND SOILS

The atomic-absorption determination of sodium is relatively easy, 

being limited by its ubiquitous nature and presence in most reagents. 

The crustal abundance is of the order of 2-4 percent, hence the element
32 ATOMIC-ABSORPTION METHODS OF ANALYSIS

is easily detected by the following procedure that has a sensitivity of 

at least 0.02 percent. As with potassium, anomalous concentrations of 

sodium require considerable dilution of sample solution before measurement.

PROCEDURE

Special reagents in addition to those listed under "General procedure" (p. 25) are given below. 

Dilution reagent: Add 20 ml concentrated hydrochloric acid to 1 liter

of metal-free water.

Standard solutions:

Sodium standard stock Concentra- Procedure 

solution tion (ppm)

A... _____________ 1,000 Dissolve 2.54 g sodium chloride in 1,000 ml of

dilution reagent. 

B... _________ _ 100 Prepare by diluting 10 ml of A to 100 ml

with dilution reagent.

C.___________ 10 Prepare daily by diluting 10 ml of .B to 100

ml with dilution reagent.

Working sodium standard solutions (to prepare 50-ml solutions of 

dilution reagent containing indicated concentrations of sodium in 

parts per million, dilute the indicated stock solutions to volume with 

dilution reagent):

Concentration Stock solution

5____ _ _ ______________ 25 ml of C.

10_____________-___-___________________________ Use C above.

20_________ ________________________________ 10 ml of B.

50____.______________---____-_._________ 25 ml of B.

Operating conditions for model 290: 

5-cm short-path burner: 

Air pressure, 30 psi. 

Acetylene pressure, 8 psi. 

Burner position:

For 0-50 ppm, burner perpendicular to source beam. 

For 0-5 ppm, burner in line with source beam. 

Counter, 783. 

Source, hollow cathode. 

Lamp current, 10 ma. 

Slit, 7 A.

Sample digestion: Refer to "General procedure" (p. 25). After 

treatment, transfer the 2 ml of warm hydrochloric acid solution to a 

50-ml volumetric flask, make up to volume with water, and nd\x.
GOLD 33

Estimation: Refer to "General procedure" (p. 25).

Discussion: Large amounts of hydrochloric acid, chlorides, and 

calcium depress the absorbance of sodium according to Rubeska, 

Moldan, and Valny (1963), but Angino and Billings (1967, p. 54) 

were unable to find any spectral interferences in determinations of 

sodium in a calcium carbonate matrix. Both Rubeska, Moldan, 

and Valny (1963) and Robinson (1960) stated that as much as 3,000 

ppm potassium had no effect on the sodium measurements.

In the proposed procedure the sample solution is about 0.2 M 

in hydrochloric acid much less than that used by Rubeska and 

coworkers. Presumably this concentration has no depressive effect 

on the absorbance of sodium.

GOLD, TELLURIUM, AND MERCURY IN ROCKS AND SOILS 

SPECIFIC PROCEDURES

GOLD

The three methods presented for atomic-absorption determination 

of gold in rocks and soils differ mainly in the size of sample taken and 

the procedure for sample dissolution. In each method the solubilized 

gold is measured by aspirating the MIBK (methyl isobutyl ketone) 

extract containing the gold into the flame of an atomic-absorption 

instrument and comparing the absorbance with that of standards 

contained in a similar matrix.

The first two methods are described in detail by Thompson, 

Nakagawa, and VanSickle (1968). Their description includes precision 

accuracy data, applications of the methods to different geologic 

materials from several geographic areas and precautions to the 

analyst to assure reliable results.

The third gold method is given in greater detail by VanSickle and 

Lakin (1968) including data on the repeatability and reliability of the 

method. Their report also includes a comparison of gold contents 

obtained by assay and other methods on different geologic materials 

including gossan, pyritic rock, and sulfide ore.

The three methods are arranged chronologically in the order of 

development as the problem of representative sampling became more 

acute and the need and demand for analytical capability increased.

PROCEDURE, FIRST METHOD

Equipment and reagents are given below.

Culture tubes, screwcap, 25- by 200-mm, with Teflon liner in cap. 

Beakers, 50 ml. 

Hotplate, oscillating.
34 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Porcelain evaporating dish, 60 mm diameter. 

Hydrobromic acid, concentrated, 48 percent. 

Hydrobromic acid, 3 M dilute 340 ml concentrated acid to 1 liter

with water. 

Hydrobromic acid, 1 M dilute 115 ml concentrated acid to 1 liter

with water.

4-methyl-2-pentanone (methyl isobutyl ketone) reagent grade. 

Sodium bromate ACS.

Standard solutions:

Gold standard stock Concentration Procedure 

solution (ppm)

A______________ 1,000 Dissolve 0.1 g gold in mixture of hydrobromic acid and bromine and heat gently 

to expel excess bromine. Cool and dilute 

to 100 ml with concentrated hydrobromic 

acid.

B.... ____________ 100 Prepare by diluting 10 ml of A to 100 ml

with 3 M hydrobromic acid.

C...--_._____ 25 Prepare by diluting 25 ml of B to 100 ml

with 3 M hydrobromic acid.

D....-___-_-_--_. 10 Prepare daily by diluting 10 ml of B to 100

ml with 3 M hydrobromic acid.

E................ 5 Prepare daily by diluting 50 ml of D to 100

ml with 3 M hydrobromic acid.

Working gold standard solutions:

To prepare 50-ml solutions of MIBK containing indicated concentrations of gold in parts per million, add indicated amounts of 

stock solutions to 30 ml of 3 M hydrobromic acid in 125-ml 

separatory funnel. Add 10 ml MIBK, stopper, and shake contents 

for 1 minute. Separate phases and transfer MIBK to 50-ml 

volumetric flask. Add MIBK to mark, mix, and add 1 ml of 1 M 

hydrobromic acid.

Concentration Stock solution

0.5__--_______________________________ 5 ml of E.

1.............................................. 10 ml of E.

2___________________________________ 10ml of D.

5__--_--_-_-----___------____________________ 10ml of C.

Optimum working range with model 303: 

Manual (XI), 0.5 through 5.0 ppm.

(X 5), 0.02 through 0.5 ppm. 

DCR, 0.02 through 5.0 ppm.
GOLD 35

Operating conditions for model 303:

Wavelength, 2430 A.

Source, hollow cathode.

Lamp current, 14 ma.

Range, ultraviolet.

Slit, 4.

Boling burner:

Air pressure, 20 psi. 

Acetylene pressure, 8 psi.

Sample digestion: Ignite 2.0 g of powdered rock or soil in porcelain 

evaporating dish for 10 minutes over Meker burner or until sulfides 

and organic matter are completely oxidized. Transfer sample to 

50-ml beaker and add 0.5 g sodium bromate. Mix sample and 

bromate thoroughly and add 15 ml concentrated hydrobromic acid. 

Place beaker and contents on oscillating hotplate and boil until 

about 5 ml of acid remains. Transfer entire contents of beaker 

(unattacked sample an,d acid) to a 25- by 200-mm screwcap tube, 

wash beaker with several portions of water, and add water to sample 

solution in the screwcap tube. Make up volume of solution hi tube 

to 35 ml with water. Add 10 ml MIBK and vigorously shake contents of tube for 1 minute. Allow tube to stand until layers separate 

or centrifuge to accomplish separation. If upper layer is colored, 

transfer it to clean tube containing 25 ml 1 M hydrobromic acid 

and shake tube and contents for 15 seconds. Repeat if necessary 

until organic layer is colorless or color ceases to change. 

Estimation: Zero instrument with MIBK and atomize the supernatant 

liquid of each working gold standard solution in the atomic-absorption instrument. Read absorbance or calculate from the percentage 

of absorption as directed under "Instrument calibration" (p. 10). 

Set up standard curve or calibrate the instrument as directed under 

"General procedure" (p. 9). Atomize the organic layer in 

the atomic-absorption spectrophotometer. Read the absorbance 

and convert to concentration as directed above for the particular 

instrument.

PROCEDURE, SECOND METHOD

Reagents other than listed under first method (p. 33) are given 

below.

Hydrobromic acid, 0.1 M: Dilute 25 ml concentrated acid to 2 liters

with metal-free water. 

Hydrobromic acid-bromine reagent: Add 10 ml bromine, sp gr 3.1, to 2

liters of concentrated hydrobromic acid.
36 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Standard solutions:

Gold standard 

stock solution

A.... ........

B..... .........

C..-. ---------

D..-. ---------

E

Concentration 

(ppm)

1,000

100

20

10

1

Procedure

Prepare by diluting 20 ml of B to 100 ml

with 3 M hydrobromic acid. 

Prepare as in method 1.

Prepare daily by diluting 10 ml of D to 100

ml with 3 M hydrobromic acid.

Working gold standard solutions:

To prepare 100-ml solutions of MIBK containing indicated concentrations of gold in parts per million, add indicated amounts 

of stock solutions to mixtures of 10 ml hydrobromic acid-bromine 

reagent and 20 ml of metal-free water in 125-ml separatory 

funnel. Add 10 ml MIBK, stopper, and shake contents for 1 

minute. Separate phases and transfer MIBK to 100-ml volumetric flask. Add MIBK to mark, mix, and add 1 ml of 1 M 

hydrobromic acid.

Concentration Stock solution

0.1 -- - __ _ __ 10 ml of B.

!__- _____ ___ _ ____ _ ______________________ 10ml of D.

2______.._ .___ .____.._.. _.__.-._______.._ 10 ml of C.

Operating conditions for model 290: 

Counter, 134.5. 

Source, hollow cathode. 

Lamp current, 5 ma. 

Slit, 7 A. 

Boling burner:

Air pressure, 30 psi. 

Acetylene pressure, 8 psi.

Sample digestion: Ignite 10 g of powdered rock or soil in porcelain 

evaporating dish for 10 minutes over Meker burner or until completely oxidized. Stir occasionally during ignition. Transfer sample 

to 25- by 200-mm screwcap tube and carefully add 20 ml of hydrobromic acid-bromine reagent. Cap tube and shake it for 15 minutes. 

Add 20 ml metal-free water and 10 ml MIBK. Cap tube and shake 

it again for 3 minutes. Centrifuge tube until layers separate and 

transfer MIBK to clean tube containing 30 ml 0.1 M hydrobromic 

acid. Shake latter tube for 20 seconds and allow phases to separate. 

Estimation: Refer to estimation under "Procedure, first method" 

(p. 35).
GOLD 37

Discussion: The solubility of MIBK! in hydrobromic acid increases 

with concentration of the latter; if the decrease in volume of the 

ketone is appreciable during extraction, additional ketone is added 

to correct for apparent loss. H. W. Lakin and G. H. VanSickle (oral 

commun., 1968) observed that with radioactive gold despite such 

losses of MIBK during extraction all the gold was in the separated 

ketone.

Infrequently a side reaction occurs when the solubilized gold is 

extracted into MIBK from 3-4 M hydrobromic acid; this reaction 

causes the organic layer to sink to the bottom of the screwcap tube. 

The odor of the heavy organic layer strongly suggests bromoform. If 

such a side reaction occurs, the analyst should continue as directed in 

the procedure but should make necessary modifications to transfer the 

bottom layer instead of the upper layer to a clean tube containing 

0.1 M hydrobromic acid.

All three procedures for gold include washing the MIBK containing 

the gold with dilute (0.1 M) hydrobromic acid to remove traces of 

iron which may interfere in the atomic-absorption measurement. The 

procedure for tellurium requires 1.0 M hydrobromic acid in place of 

the weaker acid above.

PROCEDURE, THIRD METHOD

Equipment and reagents other than listed under first and second 

methods (pp. 33, 35) are given below.

Furnace, muffle, optional. Ignition over open flame may be substituted.

Jars, glass, 6-oz. Teflon liner in caps.

Bromine, reagent-grade.

Ethyl ether, reagent-grade. Caution! See Ward, Lakin, Canney, and

others (1963, p. 5). 

Hydrobromic acid, 1.5 M. Dilute 170 ml concentrated acid to 1 liter

with water.

Standard solutions:

Gold standard stock Concentra- Procedure 

solution tion ppm

A ________________ 1, 000 Prepare as in method 1.

B______________ 100 Prepare by diluting 10 ml.of A to 100 ml with

1.5 M hydrobromic acid. 

C___-_-.___ 10 Prepare fresh by diluting 10 ml of B to 100

ml with 1.5 M hydrobromic acid. 

D______________ 5 Prepare fresh by diluting 50 ml of C to 100

ml with 1.5 M hydrobromic acid. 

#-_____--_-___ 1 Prepare fresh by diluting 10 ml of C to 100

ml with 1.5 M hydrobromic acid.
38 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Working gold standard solutions:

To prepare 50-ml solutions of MIBK containing indicated concentrations of gold in parts per million, add amounts of stock solutions given below to 20 ml of 1.5 M hybrobromic acid in 100-ml 

volumetric flask. Add 50 ml of MIBK, stopper, and shake flask 

for 1 minute.

Concentration Stock solution

0.1___.--..__.___.._....__..._--.--_-.---_-.- 5 ml of E. 

0.5 ____----_-__-.-__-__-------__-.--_----_. 5 ml of D.

1.............................................. 10ml of D.

2... ......... .................................. 10ml of C.

Operating conditions: Refer to "Procedure, second method" 

(p. 35).

Sample digestion:

1. Weigh 100 g of sample ground to 100 mesh and transfer it to a 

porcelain dish. Place dish in a muffle furnace and heat at 700°C 

for 2 hours.

2. Cool and transfer the sample to a 6-oz glass jar. Add 1 ml bromine 

and 5 ml ethyl ether. Cap the jar tightly and shake vigorously to 

mix. Allow jar to stand for about 1 hour and shake it intermittently.

3. Add 20 ml MIBK to mixture. Cap and shake vigorously to mix. 

Add more MIBK if necessary until the sample is completely wet 

and has the consistency of a soft mud ball.

4. Remove the cap and add approximately 10 ml 0.1 M hydrobromic 

acid to contents. Stir gently with a porcelain spatula. Continue 

to add 0.1 M acid in small increments and stir until MIBK is 

separated.

5. Pour off the MIBK into a 25- by 200-mm screwcap culture tube 

containing 25 ml 0.1 M hydrobromic acid. Cap the tube and 

shake it for 30 seconds.

Estimation: Aspirate the separated organic phase into an atomicabsorption spectrophotometer. Read the percent absorption and 

convert to concentration as directed for the particular instrument. 

The gold content, in parts per million, of the sample is equal to:

Mg/ml X (ml MIBK + ml ethyl ether) 

100

TELLURIUM

The following procedure is described in detail by Nakagawa and 

Thompson (1968).
TELLURIUM 39

The sensitivity of the method as described here is of the order of 0.2 

ppm, and such a sensitivity is barely adequate to measure background 

concentrations. Thus some kind of preconcentration is required.

Chakrabarti (1967) concentrated tellurium by coprecipitation with 

elemental arsenic or by forming a complex ion such as potassium 

hexaiodotellurate or tellurium diethyldithiocarbamate and extracting 

the complex ion into an immiscible solvent like methyl isobutyl 

ketone. The following procedure includes a solvent extraction step to 

enrich the tellurium to a threshold level.

PROCEDURE

For reagents, see "Procedure, first method" under "Gold" (p. 33). 

Reagents needed in addition to those listed above are given below.

Bromine, reagent-grade.

Hydrobromic acid-bromine reagent. Add 5 ml bromine to 1 liter 

concentrated hydrobromic acid.

Standard solutions:

Tellurium standard 

stock solution

Concentration (ppm)

Procedure

B.

100 Dissolve 0.0625 g tellurium dioxide in 500 ml

concentrated hydrobromic acid. 

10 Prepare by diluting 10 ml of A to 100 ml

with 3 M hydrobromic acid. 

5 Prepare by diluting 50 ml of B to 100 ml

with 3 M hydrobromic acid. 

0. 5 Prepare by diluting 10 ml of C to 100 ml 

with 3 M hydrobromic acid.

D.

Working tellurium standard solutions:

To prepare 25-ml solutions of MIBK containing indicated concentrations of tellurium in parts per million, add indicated 

amounts of stock solutions to 45 ml 3 M hydrobromic acid in 

100-ml volumetric flask. Add 25 ml MIBK, stopper, and shake 

flask for 1 minute.

Concentration Stock solution

0.1. 5 ml of D. 

5 ml of C. 

10 ml of B.

Optimum working range with model 303: 

Manual (X 1), 0.5 through 5.0 ppm. 

(X 5), 0.1 through 1.0 ppm. 

DCR, 0.1 through 5.0 ppm.
40 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Operating conditions for model 303:

Wavelength, 214° A. ;

Source, hollow cathode.

Lamp current, 18 ma.

Range, ultraviolet.

Slit, 3.

10-cm burner:

Air pressure, 20 psi. 

Acetylene pressure, 8 psi.

Sample digestion: Weigh 5 g of sample into a 50-ml beaker and add 

20 ml hydrobromic acid-bromine reagent. Place beaker on oscillating hotplate and boil solution gently until the volume of the 

solution is reduced to approximately 10 ml. Remove beaker from 

hotplate and allow to cool.

Extraction of tellurium: Transfer entire contents of beaker (acid plus 

unreacted sample) to a 25- by 200-mm test tube fitted with screwcap. Rinse beaker with three 5-ml portions of water and add 

rinse portions to tube. Add water to 30-ml mark. Add 10 ml MIBK 

and shake tube and contents vigorously for 1 minute. Let tube 

set or centrifuge until the layers separate. If the organic layer is 

colorless, proceed with estimation below; however, if the organic 

layer is colored, separate and transfer to a clean screwcap tube 

containing 25 ml of 1 M hydrobromic acid. Cap tube and shake 

it for 15 seconds. Allow phases to separate and proceed immediately 

with estimation.

Estimation: Zero instrument with MIBK and atomize the supernatant liquid of each working tellurium standard solution in the 

atomic-absorption instrument. Read absorbance or calculate from 

percentage of absorption as directed under "Instrument calibration" (p. 10). Set up standard curve or calibrate the instrument 

as directed under "General procedure" (p. 9). Atomize the 

organic extractant into an atomic-absorption spectrophotometer. 

Repeat and average the readings and convert to parts per million 

as directed above for the particular instrument. 

Discussion: The determination of tellurium by atomic-absorption 

spectroscopy is much less common than that of other elements 

described in this publication. In fact, since a sensitivity was first 

given by Allan (1962), less than a half dozen tellurium analyses 

have been reported. A reason for such scarcity is implied in one 

report by Sprague, Manning, and Slavin (1964). They studied 

among other things the variation of absorbance due to tellurium 

as a function of lamp current and obtained three different curves 

with as many hollow-cathode lamps. They also observed severe
MERCURY 41

interference due to copper lines near the most intense tellurium 

resonance line, but despite such interferences they were able to 

establish the optimum conditions for determining tellurium in 

solution.

Improved technology in hollow-cathode lamp manufacture has 

largely nullified the copper interference.

Eecently, Chakrabarti (1967) reexamined the parameters for 

atomic-absorption determination of tellurium. He observed a decreased absorption with increased lamp current similar to that 

observed by Sprague, Manning, and Slavin (1964) and reasoned that 

the decrease was due to increased Doppler broadening and also to 

self-absorption broadening of the emitted line from the hollowcathode source.

Obviously the atomic-absorption determination of tellurium is 

difficult, and the analyst should exercise extreme care to avoid 

obvious pitfalls and to develop skills in coping with possible problems 

like those discussed for gold determinations (p. 37).

MERCURY

The atomic-absorption method described below for determining 

trace amounts of mercury differs remarkably from other methods 

given in this report. First, the high volatility and vapor pressure of 

elemental mercury and several of its compounds simplify the sample 

dissolution, and second, the ability of the elemental vapor to absorb 

discrete energy frequencies simplifies the technique of sample introduction into a beam of light. Indeed, such absorption is one of the 

oldest examples of atomic absorption, and the phenomenon has provided a means of determining mercury qualitatively for nearly a 

century.

The formation of mercury halos or zones around mercury deposits 

(Saukov, 1946) and the observed association of mercury with basemetal deposits (Sergeev, 1957) created a demand for reliable quantitative methods for measuring mercury in the parts-per-billion range. 

The qualitative atomic-absorption method is extremely sensitive, and 

attempts to make such a method quantitative is a natural step. The 

success of these attempts is described by Vaughn and McCarthy 

(1964), Vaughn (1967), and Williston and Morris (1965).

PROCEDURE

Reagents and equipment are given below. 

Iron filings, sulfide-free. 

Mercury-saturated air. Prepare by placing a few grams of mercury in

a 60-ml serum bottle fitted with rubber-membrane stopper.
42 ATOMIC-ABSORPTION METHODS OF ANALYSIS

Mercury-vapor detector. Plans for assembly are given by Vaughn

(1967). 

Iron sample holders described by Vaughn (1967).

Weigh or measure by volume a 0.25-g sample of rock or soil ground 

only enough to pass through a 40-mesh sieve. Place sample into iron 

sample holder. Cover high-sulfide sample with iron filings. Place 

sample holder on cam support and raise into upright quartz tube 

(b in fig. 2, Vaughn, 1967). Open bypass cock (exhaust side in diagram 

of fig. 2, Vaughn, 1967) and heat sample to about 500°C. Allow 

smoke to pass by amalgamator and out through vent. Change bypass 

cock to mercury (in fig. 2 of Vaughn, 1967) and switch induction 

heater to amalgamator (d in fig. 2, Vaughn, 1967). Heat amalgamator 

to maximum reading on the milliammeter or other current-measuring 

device.

Refer peak current reading to previously established calibration 

curve to obtain the mercury concentration.

Instrument calibration: By means of a syringe, inject different 

volumes of mercury-saturated air into the upright quartz tube 

(b in fig. 2, Vaughn, 1967). At a given temperature the mercurysaturated air contains a definite amount of mercury. Prepare 

calibration curve by plotting the quantities of mercury injected 

versus the peak currents observed.

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