I

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NAT'L INST. OF STAND & TECH

A UNITED STAT DEPARTMENT n L qLnPIP

COMMERC A111Db 3bDE12

PUBLICATION

National Bureau of Standards

Library, E-01 Admin. Bldg. OCT 1 1981 131008

NBS SPECIAL PUBLICATION 260"3/r-a>7

U.S. DEPARTMENT

OF

COMMERCE

100

• U57

C5L

Standard Reference Materials:

METHODS OF ANALYSIS OF

NBS CLAY STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and

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1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
Brtfonal Bureau of Statferds ML 2 4 1972 Standard Reference Materials: J Methods of Analysis of

NBS Clay Standards

J. I. Shultz, R. K. Bell, T. C. Rains, and

O. Menis

Analytical Chemistry Division

Institute for Materials Research U«S< National Bureau of Standards Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretory NATIONAL BUREAU OF STANDARDS, Lawrence M; Kushner, Acting Director, Issued June 1972
Library of Congress Catalog Card Number: 72-600062

National Bureau of Standards Special Publication 260-37

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-37, 86 pages ( June 1972) CODEN: XNBSAV

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:260-37). Price 75 cents.
PREFACE

Standard Reference Materials (SRM's) as defined by the

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x NBS Special Publication - 260 Series is reserved for this

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Inquiries concerning the technical content of this

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CONTENTS

PAGE

INTRODUCTION 1 PART I 3 SILICA 3 SILICA BY THE HYDROCHLORIC ACID DEHYDRATION

(GRAVIMETRIC) METHOD 3 SOLUBLE SILICON FOLLOWING SILICA DEHYDRATION. . . 7 SILICON BY THE MOLYBDENUM BLUE- (PHOT OMETRIC)

METHOD 7 ALUMINA 12 ALUMINA BY THE SODIUM HYDROXIDE-CIT RATE-CYANIDE8-QUINOLINOL (GRAVIMETRIC) METHOD 12 ALUMINA BY THE AMMONIUM HYDROXIDE- CUPFERRON

(GRAVIMETRIC) METHOD 17 PRECIPITATION WITH AMMONIUM HYDROXIDE 20

PRECIPITATION WITH CUPFERRON 21

PHOSPHORUS 23 PHOSPHORUS BY THE MOLYBDENUM-BLUE (PHOTOMETRIC)

METHOD 23 PHOSPHORUS BY THE ION-EXCHANGE (PHOTOMETRIC)

METHOD 27 TITANIA BY CUPFERRON (GRAVIMETRIC) METHOD 30 TITANIA BY THE HYDROGEN PEROXIDE (PHOTOMETRIC) METHOD 34 IRON BY THE 1 , 1 0-PHENANTHROLINE (PHOTOMETRIC) METHOD. 37 IRON BY SnCl

2 ~K

2 Cr

2 07 (VOLUMETRIC) METHOD 40 ZIRCONIA BY THE PYROCATECHOL VIOLET (PHOTOMETRIC)

METHOD 4 3 CHROMIUM OXIDE BY THE DIPHENYLCARBAZ IDE (PHOTOMETRIC)

METHOD 4 6

vi
CONTENTS -CONTINUED

PAGE

PART II 49 ATOMIC ABSORPTION AND FLAME EMISSION SPECTROMETRY. . 49 INSTRUMENTATION 50 PROCEDURE FOR DISSOLUTION OF CLAY MATERIALS FOR

FLAME EMISSION AND ATOMIC ABSORPTION ANALYSES. . . 51

LITHIUM BY FLAME EMISSION SPECTROMETRY 52 SODIUM BY FLAME EMISSION SPECTROMETRY 55 POTASSIUM BY FLAME EMISSION SPECTROMETRY 58

MAGNESIUM BY ATOMIC ABSORPTION SPECTROMETRY 61

CALCIUM BY ATOMIC ABSORPTION SPECTROMETRY 6 6 STRONTIUM BY ATOMIC ABSORPTION SPECTROMETRY 69 BARIUM BY FLAME EMISSION SPECTROMETRY 72

REFERENCES 75 APPENDIX 1 CERTIFICATE OF ANALYSIS, STANDARD REFERENCE

MATERIAL 9 7a, FLINT CLAY 76

APPENDIX 2 CERTIFICATE OF ANALYSIS, STANDARD REFERENCE

MATERIAL 9 8a, PLASTIC CLAY 77

vii
FOREWORD

This publication describes an effective combination of

classical and instrumental analytical chemistry in characterizing a complex natural product. The attainment of

accuracy in such an analysis requires the careful

evaluation of systematic errors and the application of

appropriate corrections. Specifically, in the gravimetric

procedures, corrections for solubility and/or co- precipitation of impurities were determined by spectrophotometry procedures. Similarly, the selection of

calibration procedures and standard addition methods in

flame spectroscopy reduced the uncertainty in establishing

values for minor and trace elements. These data have led

to the certification of SRM's that were much needed for

the rapid analysis by newer methods such as X-ray fluorescence.

The latter methods, while precise, suffer from matrix effects

which require appropriate standards to calibrate these

instruments

.

viii
METHODS OF ANALYSIS OF NBS CLAY STANDARDS

J. I. Shultz, R. K. Bell, T. C. Rains and 0. Menis

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

This publication brings together a compilation of

methods used at NBS for the analysis of two complex

standard reference clay materials . The methods were

selected to give the best obtainable results for those

elements normally found in clays. In some instances,

more than one procedure was employed for an element as

a cross-check on the precision and accuracy of the

results . The procedures are presented in two parts

.

Part I is concerned with the determination of the major

constituents by the classical analytical procedures.

Part II covers the minor elements which are determined

instrumentally by flame emission and atomic absorption

spectrometry. These clay materials serve as analytical

composition standards to provide quality control of the

basic raw materials which are used in the ceramics and

refractories industries.

Key words: Atomic absorption; ceramics; classical

procedures; clay materials; flame emission;

refractories; Standard Reference Materials.

INTRODUCTION

The published methods of analysis for clays and similar

silicate materials, though fairly extensive, are widely scattered. This publication endeavors to bring together a compilation of methods used at NBS for the analysis of two complex

standard reference clay materials, plastic and flint. The

methods were selected and designed to give the best obtainable

results for those elements normally found in clays. In some instances, more than one procedure was employed for an element

as a cross-check on both the precision and accuracy of the

results . The procedures are presented in two parts . Part I is concerned with the determination of the major constituents

by the classical analytical procedures . Part II covers the

minor elements which can most conveniently be determined instrumentally by flame emission and atomic absorption spectro-
etry. These latter procedures are attractive because of their

speed, high sensitivity and improved precision and accuracy over the older and more time-consuming methods

.

With issuance of these two Standard Reference Materials,

NBS is providing renewals of materials that were first issued

in 19 31. These materials serve as analytical composition standards to provide quality control of the basic raw materials

that are used in the ceramics and refractories industries.

They will also serve as controls for the calibration of many

instrumental methods . Marked advances , in recent years , in

both instrumental and analytical techniques that are applicable

to these materials, emphasize the need for well characterized

standards

.

These natural occurring materials have complex compositions and the classical analytical procedures are both timeconsuming and difficult. To emphasize their difficulty, Lundell

and Hoffman [1] , as early as 19 28 provided data to show the lack

of agreement between analysts who assisted in the cooperative

analysis of similar materials. More recently, in 1969, Flanagan

[2] of the U.S. Geological Survey reiterated that the problem

still exists.

The preparation of the materials , prior to sampling for

analysis, consisted of sifting through a 50-mesh sieve and then

mixing in a mechanical double-cone porcelain-lined mixer for a total of 2 hours. Homogeneity for each of the clays was established by an extensive sampling procedure conducted by S. D. Rasberry of the Spectrochemical Analysis Section of the Analytical Chemistry Division. Four main samples and 4 sub -samples were tested by x-ray fluorescence for the major elements. Sixteen replicate analyses were performed for silicon, aluminum,

iron, titanium, calcium and potassium. The major elements and

minor constituents were then determined by gravimetric, titrimetric, spectrophotometric , flame-emission and atomic absorption

methods. The loss on ignition was based on heating the dried

samples for 2 hours at 1100 °C.

2
PART I SILICA

Silica is an important constituent of clays, generally

amounting to one-fifth to two-thirds of their composition.

Most of the methods for the determination of silicon are gravimetric procedures in which the silicon is converted to a soluble form by fusing with Na

2 C0

3 , Na

2 02

, K

2 S2 07

, or Na

2 S2 0^. Satisfactory fusions are obtained by using equal

parts of Na^O^ and fused Na^^O^, but the Na^^O^ must be

removed before making determinations of silica or alumina.

A satisfactory fusion is also obtained with anhydrous lithium

metaborate

.

In clays, virtually all of the silica exists in the

combined form as aluminum silicate, iron silicate, and

potassium aluminum silicate.

SILICA BY THE HYDROCHLORIC ACID DEHYDRAT ION-

( GRAVIMET RIC ) MET HOD

I. Scope

This method covers the determination of silica in

concentrations from 20 to 70 percent. The relative standard

deviation is 0.2 percent.

II. Principle of Method 13]

After fusion of the sample, silicon is converted to silicic acid with hydrochloric acid and made insoluble by

double dehydration. The solution is filtered, and the

silica is ignited, weighed, and then volatilized with

hydrofluoric acid. The residue is ignited and weighed.

The loss in weight represents silica (Si0

2

) . Soluble

silica in the filtrate is determined by spectrophotometry and

combined with that found by gravimetry.

III. Interferences

Silica is contaminated with alumina, titania, zirconia

or their phosphates, but the contaminants do not interfere

3
since they are weighed after the treatment of the impure

silica with sulfuric and hydrofluoric acids.

IV. Procedure

(a) Transfer approximately lg of sample to a weighing

bottle and dry for 2 hrs at 140 °C. Stopper the bottle

and cool for 1 hr in a desiccator. Lift the stopper for an instant, replace, and weigh the bottle and sample. Transfer

the sample, without brushing, to a 25 ml platinum crucible

containing about 1.25g of anhydrous Na2C0^ • Reweigh the

bottle. The difference is the weight of the sample.

(b) Thoroughly mix the dried sample and Na2C0^ by

stirring with a platinum rod. Add another 1.25g portion

of Na

2 C03 and mix. Repeat with a third portion of Na

2 C0

3 and mix. Use 1.25g of the Na2C0

3 to clean the stirring

rod and then cover the mixture. Heat the covered crucible

over a low flame for several min and gradually increase

the heat until the mass is molten. Using tongs, slightly

tilt and rotate the crucible to fuse any particles which

may cling to the side of the crucible above the liquid.

Heat over an open flame for 20 min. Tilt and rotate

the crucible to spread the melt around the inside of the

crucible and cool. Gently heat the crucible over an open flame for 30 sees, and cool.

(c) Cover the fused sample with water, transfer

the contents to a platinum dish or Teflon beaker and wash

the inside of the crucible and the lid. Cover the fusion

with water and allow to stand overnight. Reserve the

crucible

.

(d) Pulverize the cake and stir the solution. Place

the tip of a funnel under the cover of the dish or beaker. Add 5 ml of HC1 to the reserved crucible. Slowly

and cautiously, pour 40 ml of HC1 (1+1) through the

funnel. Transfer the contents of the reserved crucible

through the funnel . Rinse the crucible and cover with

4
water and HC1 repetitively. Wash the funnel and funnel

tip, and remove.

(e) Allow the solution to stand until reaction

ceases. Rinse the cover, replace it on the dish or beaker and heat on a steam bath until carbon dioxide

is expelled. If any insoluble residue is present, filter,

wash the residue with water, transfer the paper to the

crucible used for the fusion, and ignite at low heat

until carbon is removed. Fuse the residue with 2g of

Na

2 C0

3 and add the cooled melt to the original solution.

Wash the cover and replace it on the dish or beaker

containing glass hooks or a triangle and evaporate the

solution to dryness with occasional stirring.

(f) Add 50 ml of HC1 (1+4) to the dish or beaker,

cover, and heat for 10 min. Add 150 ml of hot HC1 (1+19)

,

stir to dissolve salts, and filter immediately by

decantation through a 11-cm medium filter paper into a 600 ml beaker. Wash the residue once with 15 ml of hot

HC1 (1+19). Transfer the bulk of the silica to the

funnel. Scrub the dish or beaker thoroughly with a rubber-tipped rod. Wash the paper and precipitate 15

times with hot HC1 (1+19) and 3 times with hot water.

Transfer the paper and contents to a platinum crucible

and reserve.

(g) Transfer the filtrate and washings to the

original platinum dish or beaker. Evaporate to dryness

on a steam bath. Add 50 ml of HC1 (1+4) , digest and

filter through a 9-cm fine filter paper. Scrub and

wash the container 10 times with hot HC1 (1+19) and 3 times with hot water. Reserve the filtrate (A) and

washings after evaporating to about 200 ml for spectrophotometry determination of soluble silica.

(h) Transfer the paper to the reserved platinum

crucible, dry and heat slowly to 600 °C until the

5
carbon is removed. Finally ignite for 1 hr at 1200 °C

to constant weight. Cool in a desiccator, and weigh

after 30 mins.

(i) Add about 1 ml of water and 6 drops of f^SO^

(1+1) to the Si0

2 precipitate. Add 15 ml of HF and

evaporate to dryness and then heat at a gradually

increasing rate until K^SO^ is removed. Ignite for

10 min at 1100 to 1150 °C, cool in desiccator, and

weigh. The difference is the weight of silica.

V. Calculation

Calculate the percentage of silica as follows:

Silica, percent = X 100

where

A = initial weight, in grams, of crucible and

impure SiC^.

B = final weight, in grams, of crucible and residue.

C = grams of sample used.

6
SOLUBLE SILICON FOLLOWING SILICA DEHYDRATION

Separation of silicon by dehydration with acid

is never complete because of the solubility of silicic

acid. Soluble silica in the filtrate from the dehydration

may be determined spectrophotometrically

.

The molybdenum blue method is a useful method for

the photometric determination of silicon up to 200 parts

per million. Molybdisilicic acid formed in a solution

containing hydrofluoric, boric, and molybdic acids

at pH 1.7 to 1.8 is extracted with butyl alcohol after

addition of tartaric acid. The heteropoly acid is

reduced with stannous chloride to the blue complex

before measuring the intensity of the color. The addition

of tartaric acid prohibits further reactions of the

molybdisilicic acid with the silica from reagents or glassware

.

SILICON BY THE MOLYBDENUM BLUE- (PHOT OMET RIC) METHOD

I. Scope

This method covers the determination of silicon

in concentrations from 5 to 20 0 ppm in filtrates from

silica separations in clays. The standard deviation

at this range is 0.0001 percent.

II. Principle of Method [4]

The filtrate from the dehydrated silica is treated

with hydrofluoric, boric, and molybdic acids and adjusted

to a pH of 1.7 to 1.8. Molybdisilicic acid is extracted

with normal butyl alcohol and reduced to a heteropoly

blue complex. The spectrophotometry measurement is made

at 635 nm. III . Interferences

The elements normally present in clays do not interfere.

Solutions should be kept in plastic containers.

7
IV. Concentration Range

The recommended concentration range is from 5 to

20 yg of silicon per 50 ml of butyl alcohol, using a 2-cm cell.

V. Stability of Color

The color is stable for at least 1 hr.

VI. Reagents

(a) Ammonium Hydroxide Solution. Bubble ammonia

gas using plastic tubing, into cooled distilled water in

a polyethylene bottle until the solution is saturated.

(b) Boric Acid Solution (50g/l) . Dissolve

50g of H^BO^ in 900 ml of warm water, cool, and dilute

to 1 liter with water.

(c) Potassium Permanganate Solution (0.6g/l).

Dissolve 0.15g of KMnO^ in 200 ml of water and dilute to

250 ml with water.

(d) Molybdic Acid Solution. Dissolve 25g of ammonium

molybdate tetrahydrate in 200 ml of H

2 S0

4 (1+9) in a 400-ml plastic beaker, dilute to 250 ml with water, and

filter through a close-textured paper in a plastic funnel

into a polyethylene bottle.

(e) Tartaric Acid Solution (200g/l) . Dissolve

50g of tartaric acid in 200 ml of water and dilute to 250 ml

with water.

(f ) Stannous Chloride Reducing Solution (20g/l)

Dissolve 2g of SnCl

2 .2H2 0 and 1 mg of CuCl2 .2H2 0 in

100 ml of HC1 (sp. gr. 1.18) and store in a glass-stoppered

bottle. This solution should be prepared fresh every

3 days.

(g) Silicon, Standard Solution (A) (1 ml - 200 ug of

Si). Fuse 213.9 mg of Si0

2 with 2g of Na

2C03 in a platinum

crucible, cool, and dissolve the melt in 200 ml of water

in a plastic beaker. Transfer the solution to a 500-ml

8
volumetric flask, dilute to the mark with water, mix well,

and store the solution in a plastic bottle.

(h) Silicon, Standard Solution (B) (1 ml ? 2 yg of Si)

.

Transfer exactly 10 ml of standard silicon solution (A) to a 1-liter volumetric flask, dilute to the mark with

water, mix well, and store in a plastic bottle.

(i) Dilute Hydrochloric Acid (20% HCl) . Add

100 ml of HCl (low in Si) , in a plastic graduate, to

300 ml of water in a plastic bottle, mix, and cool.

Dilute to 500 ml with water, and mix.

VII . Preparation of Calibration Curve

(a) Calibration solutions.

(1) Transfer 0.0, 2.5, 5.0, 7.5, and 10.0 ml

of standard silicon solution (B) to five covered 250-ml

plastic beakers. Add 10 ml of the 20% HCl solution.

(2) Add 0.5 ml of HF, mix, and allow to stand

several minutes. Add 40 ml of the boric acid solution

and 4 ml of the molybdic acid solution, mixing after

each addition. Add 3 or 4 drops of the potassium

permanganate solution, mixing after each drop. Add

1 or 2 ml of the ammonium hydroxide solution from a plastic dropper to neutralize some of the acid before using

the glass electrode. Adjust the pH of the solution to

1.7 to 1.8 with the ammonium hydroxide solution. Cover

the beaker and heat for 10 minutes on a steam bath.

Cool in water at 20 °C for 10 minutes. Add 4 ml of the

tartaric acid solution and mix thoroughly. Glassware

can be used from this point. Transfer the solution to

a 250-ml separatory funnel. Wash the beaker twice with

water and add the water to the funnel. Dilute the

solution to a volume of approximately 9 0 ml, add 14 ml

of H

2 S0

4 (1+1) , and mix. Cool to room temperature, add

50 ml of butyl alcohol, and shake vigorously for

1 minute. Allow the layers to separate, drain, and

9
discard the acid layer. Wash the butyl alcohol layer

by adding 20 ml of H

2 S04 (1+9 9) to the separatory

funnel, shaking for 30 seconds, allowing the layers to separate. Drain and discard the acid layer. Repeat

the washing 2 more times. Transfer the butyl alcohol

to a 50-ml volumetric flask. Wash the funnel twice with

small portions (1 or 2 ml) of butyl alcohol and add the

washings to the volumetric flask. Add 0.5 ml of the

stannous chloride reducing solution to the flask, dilute

to the mark with butyl alcohol, and mix.

(b) Spectrophotometry. Fill the reference cell

with normal butyl alcohol and adjust the photometer to the initial setting, using a light band centered at approximately 6 35 nm. While maintaining this photometric

adjustment, take the photometric readings of the solutions.

One or two drops of the stannous chloride reducing

solution may be added to the sample, mixed, and another

photometric reading taken to check for the complete

reduction of the molybdisilicic acid.

(c) Calibration curve. Plot the photometric

readings of the calibration solutions against the micrograms of silicon per 50 ml of solution (Note 1)

VIII. Procedure

(a) Transfer the reserved filtrate of Section IV (g)

of Dehydration-Gravimetric Method for Silica, see page 3, to a 250 ml volumetric flask, dilute to volume with water and

mix. Using a plastic pipet, transfer a 4.0 ml aliquot to a plastic covered 250-ml plastic beaker and add 10 ml of

20 percent HC1 . Proceed as directed in Section VII (a) (2) and (b) . (b) Carry a reagent blank following the same procedure and using the same quantities of all reagents.

(c) By means of the calibration curve, convert the

spectrophotometric reading of the sample solution to micrograms of silicon.
IX. Calculation

Calculate the percentage of silica as follows:

n .„ i_ (A-B) X 2.14 Si0

2

, percent = —c x 1Q

where

:

A = micrograms of Si in 50 ml of butyl alcohol extract

of the aliquot portion of the sample.

B = micrograms of Si in 50 ml of butyl alcohol extract

of the blank.

C = gram of sample in 50 ml of butyl alcohol

extract of the sample.

Add the silica percent obtained by spectrophotometry to that obtained by gravimetry for the total percent silica

in the sample

.

Note 1 - Plot absorbance A, against the respective

concentrations on ordinary graph paper; or concentration C,

against percentage transmission on semi-logarithmic paper

using the semi-log scale for the percentage T values.

11
ALUMINA

Alumina is an important constituent in clays; with

silica it constitutes more than 82 percent of the clay

standards. An accurate determination of aluminum in

rocks, minerals and ceramic or metallurgical products is

difficult for the analyst. Care must be taken to avoid

contamination of aluminum with iron, titanium, zirconium,

vanadium, phosphorus, and silicon. Improper ignition of

the aluminum hydroxide precipitate and erroneous corrections for the impurities in the ignited product are sources of error. The caustic-citrate-cyanide-8-quinolinol

gravimetric method eliminates contamination of the aluminum

precipitate, which is dried in an oven, and thus avoids the

necessity of an ignition at high temperature.

In another method for alumina in clays, the sample

solution is divided into three aliquots. In the first

aliquot, A1

2

C> 3 , Fe

2 °3 ' Ti02' Z r02 ' P 2°5 ' Cr2°3 and V2°5 are precipitated with NH^OH . In the second aliquot of

the same volume , Fe

2 0

3

, T i0

2

, Z r0

2 and V2

0,- are precipitated with cupferron. In the third aliquot, P

2 0

5 is determined. Al 2°3 is then determined by difference.

ALUMINA BY THE SODIUM HYDROXIDE-CITRATE-CYANIDE

8 -QUINOLINOL- (GRAVIMETRIC) METHOD

I. Scope

This method covers the determination of alumina in

concentrations from 20 to 70 percent. The relative

standard deviation is 0.2 percent.

II. Principle of Method 151 Silicon is separated with hydrofluoric acid. Titanium

iron and zirconium are separated with sodium hydroxide.

The alkali salts and magnesium are removed with ammonium

hydroxide and aluminum is then precipitated with 8-

quinolinol in an ammoniacal solution containing ammonium

citrate, hydrogen peroxide and sodium cyanide and weighed.

12
III. Interferences

Aluminum is separated from phosphorus, arsenic,

fluorine and boron by precipitation with 8-quinolinol

in an ammoniacal solution. Titanium, vanadium, chromium,

molybdenum, tantalum, and niobium do not interfere if

precipitation is made in ammoniacal solutions containing

hydrogen peroxide. Iron, copper, cobalt, nickel and

zinc form complex ions with cyanide in ammoniacal

solutions containing alkali cyanide and do not interfere.

IV. Reagents

(a) Citric Acid Solution (500g/l) . Dissolve 50g of

citric acid monohydrate in 50 ml of warm H

2 S04 (1+4 9) , dilute to 100 ml with water, and filter.

(b) 8-quinolinol Solution (80g/l) . Dissolve 8g of

8-quinolinol in 12 ml of acetic acid, dilute to 100 ml

with water at 60 °C, cool and filter.

(c) Cyanide Solution (400g/l) . Dissolve 40g of NaCN

in 50 ml of warm water, dilute to 100 ml with water,

and filter.

(d) Ammonium Hydroxide Solution. Bubble ammonia gas,

using plastic tubing, into chilled distilled water in a polyethylene bottle until the solution is saturated.

(e) Hydrogen Peroxide- (3 percent).

(f) Wash Solution- (2 percent). Dissolve 20g each of

ammonium tartrate, sodium cyanide, and ammonium chloride ii 1-liter of water.

V. Procedure

(a) Transfer approximately 0.5g of sample (use a sample weight containing not more than O.lg of aluminum)

to a weighing bottle and dry for 2 hrs at 140 °C. Stopper

the bottle and cool 1 hr in a desiccator. Lift the

stopper momentarily, replace, and weigh the bottle and

sample. Transfer the sample, without brushing to a 1-liter platinum dish. Reweigh the bottle.

13
(b) Add 15 ml of water, 10 ml of H

2 S04

, 15 ml of

HN0

3

, and 12 ml of HF to the covered dish and mix.

Digest on a steam bath for 30 min with occasional stirring.

Remove and wash the cover. Rinse the wall of the dish

thoroughly and evaporate the solution to fumes of H

2

SC> 4. Cool, rinse the wall of the dish, mix and again evaporate

to fumes of H

2 S0

4

. Cool, wash, mix and evaporate again.

Complete removal of fluorine is essential. Cool, cautiously

add 100 ml of warm water, and heat until the salts are in

solution. Add paper pulp and filter through a 9-cm fine

filter paper into a 60 0-ml beaker. Wash the paper

thoroughly with hot water, and reserve the filtrate (A).

(c) Transfer the paper and residue to a platinum

crucible and ignite at 600 °C. Cool, add 2 ml of water,

5 ml of H

2 S0

4 (1+1) and 5 ml of HF . Evaporate to fumes of H

2 S0

4 on a sand bath. Cool, wash the wall of

the crucible with water, mix and evaporate to fumes of

H

2 S04

. Cool, add 15 ml of water, mix, heat, and filter

through a 7-cm fine filter paper containing paper pulp.

Wash thoroughly with hot water. Combine the filtrate

with the reserved filtrate (A)

(d) Transfer the paper and residue to a platinum

crucible and ignite at 600 °C. Cool, add 0.6g of Na

2 C0

3

, cover and fuse over an open flame for 20 min. Cool,

add 15 ml of water, and digest on a steam bath. Transfer

the contents to a 250-ml Teflon beaker or a platinum

dish, cover, and add 10 ml of H

2 S04 (1+1) . Heat on

a steam bath to expel C0

2

. Remove and rinse the cover. Rinse the wall of the beaker or dish, add 5 ml

of HF, mix and evaporate to fumes of H

2 S0

4

. Cool,

rinse the wall of the beaker with water, mix, and again

evaporate to fumes. Cool, add 25 ml of water, heat, and

combine the solution with reserved filtrate (A)

14
(e) Slowly add NaOH solution (40%) to the combined

filtrates (A) , while stirring, until the solution is nearly

neutralized. Heat on a steam bath and pour contents slowly

into a 600-ml Teflon beaker containing 100 ml of hot NaOH

solution (10%) . Heat the solution to boiling and boil for 2 min. Allow the precipitate to settle. Place a 9 -cm medium

filter paper in a plastic funnel and wash the paper with

50 ml of hot NaOH solution (5%) . Discard the wash solution.

Filter, collecting the hot NaOH solution in a platinum dish

and wash well with hot NaOH solution (5%) . Reserve the

filtrate and washings (B)

.

(f) Dissolve the precipitate on the paper with 50 ml

of hot H2SO4 (1+5) , collecting the solution in the original

beaker. Wash thoroughly with hot H

2 S04 (1+9 9) . Nearly

neutralize the solution with NaOH. Heat gently and pour

into 50 ml of hot NaOH (10%) solution. Heat to boiling

and boil for 2 min, allow precipitate to settle. Filter

the solution through a plastic funnel containing a 9-cm

filter paper. Wash well with hot NaOH solution. Combine

the filtrate and washings with the reserved filtrate (B) and evaporate to a volume of about 300 ml.

(g) Neutralize the solution with HC1 and add a few

drops excess. Transfer to a 600-ml beaker and digest

on the steam bath. Adjust the solution to pH 7 with the

specially prepared NH^OH . Digest on a steam bath for 30 min.

Check the pH of the solution with a pH meter and adjust to pH 7, if necessary. Filter the precipitate through a 11-cm

medium filter paper and wash 5 times with hot, neutral NH

4 C1

solution (2%). Discard the filtrate and washings.

(h) Transfer the paper and contents to a 300-ml Kjeldahl

flask. Slowly add 10 ml of H

2 S0

4

. Digest for about

15 min. Add 25 ml of HN0

3 and digest on a steam bath for

15 min. Heat over an open flame until most of the HN0

3 is expelled. Cautiously add 5 ml HN0

3 and heat to fumes

15
of H

2 S0

4

. Continue the addition of HN0

3 and the heating

until organic matter is destroyed. Cool, add 10 ml of

water and evaporate until fumes of I^SO^ appear. Cool,

add 9 0 ml of water, and digest on a steam bath. Filter

the solution through a 9-cm fine filter paper catching

the filtrate in a 6 00-ml beaker. Wash thoroughly with

hot water. Discard the filter paper.

(i) Add 5 ml of the citric acid solution, and dilute

to about 325 ml. Add 10 ml of H

2 °2 ^ 3% ^ ' neutralize with

the specially prepared NH^OH and add 10 ml in excess. Add 5 ml of the NaCN solution and heat to 60 °C. Remove

from the heat, slowly add 25 ml of 8-quinolinol solution

and stir vigorously for 15 min. (Use 0.22 ml of the

acetic acid solution of 8-quinolinol per mg of aluminum, plus

2 ml excess) . Avoid a large excess of the 8-quinolinol

solution to prevent contamination of the aluminum precipitate

with reagent. Digest on top of a steam bath for 15 min.

Cool the solution to room temperature and filter, using

moderate suction, through a weighed 35-ml fritted glass

crucible of fine porosity. Wash 8 to 10 times with the

cool wash solution and 5 to 10 times with hot water.

Finally wash with cold water until the washings are colorless

.

(j) Dry the crucible and contents at 14 0 °C for

1.5 hr. Cool for 1 hr in a desiccator and weigh. Repeat,

if necessary, to constant weight.

VI. Calculation

Calculate the percentage alumina as follows

A1

2 0

3

, percent = A X O- 1109

x 100

where

:

A = grams of aluminum oxyquinolinol , and

B = grams of sample used.

16
ALUMINA BY THE AMMONIUM HYDROXIDE-CUPFERRON-

( GRAVIMETRIC) METHOD

I. Scope

This method covers the determination of alumina in

concentrations from 20 to 70 percent. The relative standard

deviation is 0.36 percent.

II. Principle of Method TU

Silicon is removed with hydrofluoric acid. An aliquot

portion is treated with ammonium hydroxide and the impure

Al

2 0

3 is ignited and weighed. Another aliquot portion of

the same volume is treated with cupferron and the

precipitate is ignited and weighed. Phosphorus is

determined in a third aliquot spectrophotometrically by

the molybdenum blue method. The percent P

2 °5 ^n t*ie sample is calculated. The weights of the oxides in the

cupferron precipitate and the Si0

2 in the NH^OH precipitate

are deducted from the weight of the impure A1

2 0

3

. The

percentages of Al

2 0

3 + ?

2 05 + Cr2°3 are determined and

the alumina is obtained by deducting the percents of

P

2 0

5 and Cr

2 0

3

. III. Interferences

The amount of chromium in the NH^OH precipitate is

uncertain due to possible oxidation during solution of the

sample. Any Cr

2 0

3 in the precipitate may be partially

oxidized during ignition. The separation of chromium may

be assured by its oxidation to the sexivalent state after

dissolution of the sample or it may be determined on another sample.

IV. Reagents

(a) Ammonium Hydroxide Solution. Proceed as directed

in Section IV of 8-quinolinol method. See page 13.

17
(b) Cupferron Solution (60g/l) . Dissolve 6g of

cupferron in 8 0 ml of cold water, dilute to 100 ml, and

filter. Prepare fresh as needed.

V. Procedure

(a) Transfer 2g of sample to a weighing bottle and

dry for 2 hr at 140 °C. Stopper the bottle and cool 1 hr

in a desiccator. Lift the stopper momentarily, replace,

and weigh the bottle and sample. Transfer the sample,

without brushing, to a 1-liter platinum dish. Reweigh

the bottle.

(b) Add 25 ml of water, 15 ml of H

2 S0

4

, 25 ml of

HN0

3

, and 20 ml of HF to the covered dish and mix.

Digest on a steam bath for 30 min, with occasional

stirring. Remove and wash the cover. Rinse the dish

thoroughly, evaporate the solution to fumes of H

2 S0

4 and

cool. Rinse the dish, mix, evaporate to fumes of I^SO^,

cool and repeat this operation. Cautiously add 100 ml of warm water, and heat until the salts are in solution. Add

paper pulp, and filter through a 9 -cm fine filter paper

into a 40 0-ml beaker. Wash the paper thoroughly with

hot water and reserve the filtrate (A)

.

(c) Transfer the paper and residue to a platinum

crucible and ignite at 600 °C. Cool, add lg of Na

2 C03

, cover, and fuse over an open flame for 15 min. Cool

and transfer the crucible and lid to a 250-ml Teflon

beaker. Add 50 ml of water and heat on a steam bath

to dissolve the fusion. Acidify the solution with

H

2 S0

4 (1+1) and add 1 ml excess. Remove the crucible

and lid and rinse. Filter the solution through a 9-cm

fine filter paper containing paper pulp and wash

thoroughly with hot water. Combine the filtrate with

reserved filtrate (A)

.

18
(d) Transfer the paper and residue to a platinum

crucible and ignite at 600 °C. Cool, add 2 ml of

water, 5 ml of H

2 S0

4 (1+1) and 5 ml of HF . Evaporate

to fumes of f^SC^ on an air bath. Cool, rinse the

crucible with water and mix. Evaporate to fumes of

H

2 S04

. Cool, add 15 ml of water, and add the solution

to the reserved filtrate (A)

.

(e) Warm a 500-ml volumetric flask at 110 °C, insert

a glass tube, and remove moisture by means of a vacuum. Stopper the flask and cool to room temperature. Weigh

the flask to the nearest milligram, using a second

flask as a tare. Transfer the reserved filtrate (A) to the weighed flask, dilute to the mark with water, and

mix. Reweigh the flask and solution, using the tare.

(f) Using a pipet, transfer 100 ml of the solution to

a weighed 6 00-ml beaker containing a cover. Reweigh the

covered beaker and solution immediately to the nearest

milligram. Reserve aliquot (A) for precipitation with

ammonium hydroxide.

(g) Using a pipet, transfer another 100 ml of

the solution to a weighed 400-ml beaker containing a cover. Reweigh the covered beaker and solution

immediately to the nearest milligram. Reserve aliquot

(B) for precipitation with cupferron.

(h) Using pipets , transfer duplicate 4-ml aliquot

portions of standard clay solution SRM 9 7A, and duplicate

15 -ml aliquot portions of standard clay solution SRM 98A,

to four 125-ml Erlenmeyer flasks. Reserve these

aliquots (C) and (D) , respectively for the determination

of phosphorus spectrophotometrically

.

19
PRECIPITATION WITH AMMONIUM HYDROXIDE

(A1

2 0

3 , Fe

2 0 3/ Ti02 , Zr02 , P2 0

5

, V

2 °5' Cr2°3 )

(i) Dilute the reserved aliquot (A) , above, to 350 ml

with water and heat on a steam bath. Adjust the solution to pH 7.0 with the specially prepared NH^OH. Heat to boiling

and boil for 2 min. Allow the precipitate to settle.

Check the pH of the solution, and adjust to pH 7.0, if

necessary. Filter the precipitate through a 12.5 cm medium filter paper and wash 5 times with hot, neutral

NH

4 C1 solution (2 percent). Discard the filtrate.

(j) Transfer the paper and contents to the original

beaker. Add 50 ml of hot HC1 (1+1) and stir to dissolve the

precipitate and to macerate the paper. Dilute to 350 ml

with hot water. Adjust the solution to pH 7.0 with NH^OH

.

Heat to boiling and boil for 2 min. Allow the precipitate

to settle. Check the pH of the solution and filter on

a medium filter paper. Do not allow the precipitate to run dry. Wash with 150 ml of hot, neutral NH

4 C1 solution

(2 percent) , keeping the filter paper nearly filled. Drain

thoroughly and transfer the paper and contents to a weighed

platinum crucible.

(k) Dry and heat slowly to 600 °C, until the carbon is

destroyed and finally heat at 1200 °C for 1 hr. Cover the

crucible, transfer to a desiccator and weigh after 30 min.

Reheat the crucible at 1200 °C for 3 min, cool in a desiccator and weigh. Reheat and reweigh, if necessary, to constant weight within 0.2 mg. The weighed precipitate

contains A1

2 0

3

, Fe

2 0

3

, Ti0

2

, Z r0

2

, p

2 0

5 > V2°5 and some Cr2°3-

(1) Add 4g of potassium pyrosulfate to the crucible

and fuse over a low flame until a clear solution is

obtained. Cool and transfer to a 150-ml beaker. Add

100 ml of H

2 S0

4 (1+9) and heat on a steam bath to dissolve

the melt. Remove and rinse the crucible. Evaporate the

20
solution to fumes of H

2 S04

, cover and fume for 5 min. Cool,

dilute to 125 ml with warm water and heat. Filter and wash

well with hot water. Transfer the paper to a platinum

crucible, dry and heat to 600 °C. Finally, heat the crucible

at 1200 °C for 30 min. Cover the crucible, cool in a desiccator and weigh. Moisten the precipitate with 3 drops

of water, add 3 drops of H

2 S0

4 (1+1) and 5 ml of HF . Heat

on an air bath to fumes of H

2 S0

4 and continue heating to expel I^SO^. Ignite the crucible over an open flame for

5 min with the cover open. Cool in a desiccator for 30 min

and weigh. The difference in weight is the silica in the

NH^OH precipitate.

PRECIPITATION WITH CUPFERRON (Fe^, TiC>

2

, Z rC> 2

, (m) Neutralize the reserved aliquot (B) with the

specially prepared NH^OH and then acidify with H

2 S0

4 (1+1) . Add 40 ml of H

2 S04 (1+1), dilute to 175 ml with water, and

stir. Cool the solution in an ice bath. Add slowly 25 ml of

cold cupferron solution (6 percent) and stir. Digest in an ice bath for several min, add paper pulp and stir. Using

moderate suction, filter the precipitate through a 11-cm

fine filter paper supported by a platinum cone in a funnel.

Wash thoroughly with chilled HC1 (1+9) containing 25 ml of

cupferron solution per liter. Transfer the paper and contents

to a platinum crucible. Heat slowly at 600 °C until the

carbon is destroyed.

(n) Cool and add 3g of K

2 S

2 0

7 and fuse over a low flame

until a clear solution is obtained. Cool, transfer the

crucible to 400-ml beaker and add 100 ml of H

2 S0

4 (1+9). Heat

to dissolve the fusion, remove and rinse the crucible. Dilute

to 170 ml with H

2 S0

4 (1+9) and add 5 ml of H

2 S04 (1+1). Cool

in an ice bath, add 2 5 ml of cold cupferron solution and add

paper pulp. Filter and wash the precipitate as directed in

the preceding paragraph. Transfer the paper and contents to a

21
weighed platinum crucible. Dry at 50 °C. Heat slowly to

600 °C until carbon is destroyed and finally heat at 1200 °C

for 1 hr. Cover the crucible, transfer to a desiccator, and

weigh after 30 min. Reheat the crucible at 1200 °C for

30 min, cool in a desiccator and weigh. Reheat and reweigh,

if necessary, to constant weight within 0.2 mg. The weighed

precipitate contains Fe^O^, Ti°2 ' an<^ V2°5* Reserve

the oxides for the gravimetric determination of titania.

VI. Calculation

See page 28.

22
PHOSPHORUS

A useful procedure for the spectrophotometric determination of phosphorus involves the phosphomolybdenum blue

complex. The method is based on the measurement of the blue

color which develops when a heteropoly acid formed by

phosphate and molybdate is reduced with hydrazine sulfate,

hydroquinone , ferrous sulfate, or sodium bisulfite. Arsenic

and germanium form yellow heteropoly acids which produce a blue color on reduction. Arsenic and germanium can be

volatilized by fuming with hydrochloric and hydrobromic

acids

.

Phosphorus can also be determined by the phosphovanadomolybdate method which is based on the formation of

a yellow complex, but the molybdenum blue method is the more

sensitive

.

A dependable gravimetric method for phosphorus involves

its precipitation as ammonium phosphomolybdate and conversion

to magnesium pyrophosphate.

PHOSPHORUS BY THE MOLYBDENUM-BLUE (PHOTOMETRIC) METHOD

I. Scope

This method covers the determination of phosphorus

pentoxide in concentrations from 0.03 to 1.5 percent. The

relative standard deviations at the low and high ranges

are 0.002 and 0.1 percent, respectively.

II. Principle of Method 16]

Phosphorus as the ortho acid forms a blue complex with

hydrazine sulfate and ammonium molybdate. Photometric

measurement is made at 650 nm.

III. Interferences

Arsenic above 0.05 percent interferes and must be

separated by volatilization with HBr. Germanium, if present,

will be removed by treatment with HBr and HCl.

23
IV. Concentration Range

The recommended concentration range is from 0.001 to 0.04

mg of phosphorus per 50 ml of solution, using a 2-cm cell.

V. Stability of Color

The color develops within 5 min at 98 °C and is stable

for at least 24 hr. Readings are usually made within 30 min.

VI. Reagents

(a) Ammonium Molybdate Solution (2 percent in 11 N I^SO^)

Add 300 ml of H

2 S0

4 (sp gr 1.84) to 500 ml of water and cool.

Dissolve 20g of ammonium molybdate in the acid and dilute

to 1 liter with water.

(b) Ammonium Molybdate - Hydrazine Sulfate Solution.

Dilute 25 ml of the ammonium molybdate solution to 80 ml

with water, add 10 ml of the hydrazine sulfate solution, and

dilute to 100 ml with water. This solution is not stable

and should be prepared as needed.

(c) Hydrazine Sulfate Solution (0.15 percent). Dissolve

1.5g of hydrazine sulfate in 1000 ml of water.

(d) Phosphorus, Standard Solution (A) (1 ml - 0.4 mg

of P) . Dissolve 1.8312g of Na

2 HP0

4 in 200 ml of water,

add 35 ml of HNO^ (1+1) , dilute to 1 liter in a volumetric

flask with water and mix.

(e) Phosphorus, Standard Solution (B) (1 ml - 0.01 mg P)

Using a pipet, transfer 5.0 ml of standard phosphorus

solution (A) to a 20 0-ml volumetric flask, dilute to the

mark with water and mix. Prepare this solution fresh as needed

(f) Sodium Sulfite Solution (10 percent) . Dissolve

lOOg of anhydrous Na2SO^ in 500 ml of water and dilute to

1 liter. Filter through a fine filter paper, but do not

wash.

VII. Preparation of Calibration Curve

(a) Transfer 0, 0.5, 1.0, 2.0, 3.0 and 4 . 0 ml aliquot

portions of standard phosphorus solution (B) to six 125-ml

Erlenmeyer flasks.

24
(b) Add 5 ml of HN0

3 (1+1) and 3.0 ml of HC104 (60

percent) . Evaporate to fumes and fume gently 3 or 4 min to remove HNO^

.

(c) Cool and add 5 ml of HBr (1+4) . Evaporate to fumes

and fume gently to remove HBr. Cool, rinse the flask with

5 ml of water and evaporate to fumes. Cool somewhat, and

add 10 ml of water and 15 ml of Na

2 S0

3 solution. Heat to boiling and boil gently for 30 sec. Add 20 ml of the

ammonium molybdate-hydrazine sulfate reagent, heat to 95-

98 °C and digest at this temperature for 4 to 5 min. Then

heat the solution just to boiling temperature, but do not

boil. Cool rapidly to room temperature and transfer the

solution to a 50-ml volumetric flask. Rinse the 125-ml

flask with 2-ml portions of a dilute solution of the

ammonium molybdate-hydrazine sulfate reagent (1+4) and

transfer the washings to the 50-ml flask. Dilute to the

mark with the diluted solution of the reagent and mix.

(d) Transfer a portion of the solution to a 2-cm

absorption cell and measure the transmittance or absorbance

at 650 nm, using water as a reference solution for 100

percent transmittance or zero absorbance. Plot the values

obtained against milligrams of phosphorus per 50 ml of

solution. (Note 1, see page 11.) VIII. Procedure

(a) Proceed as directed in Section VII, b through d

(above) , with reserved aliquots C and D prepared in

Section V, h of method for determination of Alumina by

Ammonium Hydroxide-Cupferron . See page 17.

(b) From the value obtained, determine the milligrams

of phosphorus present in 50 ml of the final solution.

(c) Carry a reagent blank through the entire procedure

using the same amounts of all reagents but with the sample

omitted

.

25
IX. Calculation

Calculate the percentage of phosphorus pentoxide as follows

:

p

2 o5

, percent _ a

-

where

:

A = milligrams of phosphorus found in 50 ml of

final test solution.

B = milligrams of phosphorus found in 50 ml of the

reagent blank, and

C = grams of sample in 50 ml of the final test

solution

.

26
PHOSPHORUS BY THE ION-EXCHANGE (PHOTOMETRIC) METHOD

I. Scope

This method covers the determination of phosphorus

pentoxide in concentrations from 0.03 to 1.5 percent.

II. Principle of Method [6, 7, 8] After fusion of the sample with lithium metaborate,

the fusion is stirred in water containing cation exchange

resin. Si0

2 , B

2 °3 and P2°5 are eluted with water. Silica is

separated with HF and phosphorus is determined spectrophotometrically

.

III. Interferences

Arsenic and germanium interfere and must be separated

by volatilization with HBr and HC1.

IV. Reagents

(a) Lithium Metaborate, Anhydrous, LiB0

2

. (b) Resin, Cation Exchange, Dowex 50W-X4 (100-200 mesh).

V. Procedure

(a) Transfer 0.5g of clay SRM 97A or 0 . 3g of clay SRM 98A

sample to a weighing bottle and dry for 2 hr at 140 °C. Cool

for 1 hr in a desiccator, and weigh the bottle and sample

after opening the bottle momentarily. Transfer the sample

to glazed paper and reweigh the bottle. The difference

is the weight of the sample. Add 2.5g of LiB0

2 to the

glazed paper and mix thoroughly. Transfer to a graphite

crucible and fuse in a muffle furnace at 95 0 °C for 20 min.

Remove the crucible, and transfer the fusion to a 400-ml

Teflon beaker containing 100 ml of water, and stir.

(b) Decant the aqueous solution into a Teflon beaker and reserve (A). Transfer the fusion to an agate mortar, grind

to a powder, and transfer to the beaker containing the water

(A) . Add double the milliequivalent weight of dry cation resin

Dowex 50W-X4 required for the aluminum and lithium. Stir for

one hr and allow to settle. Decant the solution and reserve

(B) . Transfer the resin to a column containing a plug of

27
polyethylene wool and transfer the reserved solution (B) to the column. Adjust the flow rate to 35 to 4 5 drops per min.

Elute with 400 ml of water and reserve the eluted solutions (C) , which contain SiC^ , B 2°3' an<^ P 2°5 " Elute with

25 ml of water and test for the presence of silicon spectrophotometrically

(c) Add 10 ml of HCIO^ to the reserved solution (C) and

evaporate the solution of standard 97A to a volume of about

225 ml or the solution of standard 98A to a volume of about

90 ml. Transfer the former to a 250-ml volumetric flask or

the latter to a 100-ml volumetric flask. Dilute to mark

with water, and mix.

(d) Using pipets, transfer a 10-ml aliquot portion of

standard 97A or a 20-ml aliquot of 98A to a platinum

crucible. Add 2.6 ml or 1.0 ml of HCIO^ to the crucibles

containing 97A and 98A, respectively. Add 10 ml of HF and

evaporate to fumes in an air bath. Cool, rinse the crucible,

and mix. Again evaporate to fumes of HCIO^ . Proceed as directed in Section VII (c) , (d) , of the method for the

determination of Phosphorus by the Molybdenum-Blue

(Photometric). See page 23.

The value obtained for phosphorus is calculated as

P

2 °5 and deducted from the impure A^O^ precipitate obtained

in the determination of alumina by the Ammonium HydroxideCupferron-Gravimetric Method. See page 17. Chromium is determined as C^O^ in a subsequent section

and is also deducted from the impure A^O^. See page 46.

VI. Calculation

Calculate the percentage alumina as follows:

E = —

- p

(B + C > X 100

A1

2 0

3

, (percent) = E - (F + G)

where

28
A = grams of oxides in the

aliquot portion,

B = grams of oxides in the

aliquot,

C = grams of silica in the

D = grams of sample in 100

E = percent A^O^ + P

2 °5 +

F = percent P

2 °5' and

G = percent Cr 9 0~.

NH^OH precipitate in 100 ml

cupferron precipitate in 100 ml

NH^OH precipitate,

ml aliquot,

Cr

2 0

3

,

29
TIT ANIA BY CUPFERRON (GRAVIMETRIC) METHOD

I. Principle of Method [1] After separation of silica with HF, iron, titanium,

zirconium, and vanadium are precipitated with cupferron.

The ignited oxides are fused with K

2 S

2 07 and dissolved in

H

2 S04

. Iron, titanium, and zirconium are separated from

vanadium by precipitation with NaOH solution. The

precipitate is dissolved in HC1. Tartaric acid is

added, and the solution is treated with H

2 S. Iron, in

the filtrate, is removed as FeS by ammoniacal precipitation with H

2 S. Titanium and zirconium are precipitated with cupferron and the ignited oxides are weighed. After fusion with K

2 S

2 0

7

, silica is

dehydrated, determined, and the weight of the oxides

corrected for silica. Hydrogen peroxide is added,

zirconium is precipitated with (NH

4

) 2 HP0

4 and ignited to ZrP

2 0^ and weighed. The gravimetric value for T i02 is

obtained by deducting the weight of the zirconium as Zr0

2 from the combined weight of Zr0

2 + Ti02

» II. Reagents

(a) Cupferron (60g/l) . Dissolve 6g of cupferron in

80 ml of cold water, dilute to 100 ml, and filter. Prepare

fresh as needed.

(b) Diammonium Hydrogen Phosphate. [ (NH^

)

2 HPO^] . (c) Hydrogen Peroxide Solution. (H

2 02

) 30 volume

percent.

(d) Hydrogen Sulfide. (H

2 S)

.

(e) Tartaric Acid. Reagent grade.

(f) Wash Solution. Dissolve 5g of NH

4 C1 in 1 liter of

water, add 15 ml of NH^OH, and saturate with H

2 S. III. Procedure

(a) Fuse the reserved oxides of iron, titanium,

zirconium, and vanadium, Section V, (n) of the AluminaCupferron-Gravimetric Method, with 3g of K

2 S2 0

7

. See page 22

30
Cool and transfer the crucible to a 250-ml beaker. Add

100 ml of H

2 S04 (1+9) and heat to dissolve the fusion. Wash

and remove the crucible and lid.

(b) Nearly neutralize the solution with NaOH solution

(20 percent) . Pour slowly, with constant stirring, into

100 ml of NaOH solution (10 percent) contained in a platinum or Teflon container. Digest for 1 hr on a steam

bath. Filter on a filter paper previously washed several

times with NaOH solution (10 percent) and wash the precipitate with hot water. Discard the filtrate.

(c) Dissolve the precipitate by pouring 25 ml of hot

HC1 (1+2) onto the paper and wash with hot HCl (2+98) . Add

5g of tartaric acid to the solution and dilute to 200 ml

with water. Neutralize with NH^OH and then add 2 ml of HCl

per 100 ml of solution. Heat to boiling and saturate the

solution with H

2 S to precipitate any platinum. Allow to cool

and filter through a fine filter paper. Wash with H

2 S04 (1+9)

saturated with H

2 S. Discard the precipitate.

(d) Add NH^OH to the filtrate until a black precipitate

of iron sulfide forms and then add 5 ml in excess. Treat

the solution with a rapid stream of H

2 S for 5 min. Digest

at about 40 ° C for 30 min and then filter through a fine

filter paper. Wash with H

2 S wash solution. Discard the

filter and precipitate.

(e) Evaporate the filtrate to a volume of about 155 ml

and acidify with H

2 S04

- Add 45 ml of H

2 S04 (1+1) and chill

the solution in ice water. While stirring, add 25 ml of the

cooled cupferron solution (60g/l) . Add paper pulp and

allow to settle for several mins. Insert a platinum cone in

a funnel and filter the solution on a fine filter paper using

gentle suction. Wash thoroughly with cool HCl (1+9)

containing 25 ml of the cupferron solution.

(f) Transfer the paper to a weighed platinum crucible,

cautiously char and heat at 1200 °C for 15 min. Cool and

31
weigh as Zr0

2 + T i°2* Repeat the heating and weighing to constant weight.

(g) To correct for small amounts of silica in the weighed

oxides, fuse the oxides with lg of K

2 S

2 07

. Dissolve the fusion

in 50 ml of H

2 S0

4 (1+9) and evaporate the solution to fumes

of H

2 S0

4

. Cool, add 45 ml of water, and heat until salts have

dissolved. Filter immediately through a 9-cm fine filter

paper and wash with hot H

2 S04 (1+9) . Reserve the filtrate

(A) and washings for the precipitation of zirconium.

Transfer the paper and contents to a platinum crucible,

char the paper, and ignite the crucible at 1200 °C for 10 min.

Cool and weigh. Add several drops of H

2 S0

4 (1+1) , 5 ml of HF

(48 percent) and evaporate to dryness on an air bath. Ignite

at 1000 °C for 5 min, cool and weigh. The difference in

weight is the weight of the silica in the oxides.

(h) Add 2 ml of H

2 02 (30 percent) to the reserved

filtrate (A) to oxidize titanium. Add 0.5g of (NH

4

) 2 HP0

4 to precipitate zirconium. Stir and digest overnight at about

40 °C. Filter on a 9-cm fine filter paper containing paper pulp

and wash with cold NH^NO^ solution (5 percent). Transfer the

paper to a platinum crucible, and ignite at 1050 °C. Cool, and

fuse with lg of K

2 S2 0

7

. Transfer the crucible and fusion to

a 250 ml beaker. Dissolve the fusion in 50 ml of H

2 S04 (1+9) . Remove and rinse the crucible with H

2 S0

4 (1+9) . Add

2 ml of H

2 0

2 (30 percent) and precipitate the zirconium as before. Transfer the paper to a weighed platinum crucible and

ignite at 1050 °C for 15 min. Cool and weigh the zirconium

as Z rP

2 0

7

. IV. Calculation

Calculate the percentage titania as follows

:

Ti0

2

, percent = A " ^

B + C) X 100

where

:

A = grams of mixed oxides, T i09 + Zr09 + Si09

,

32
B = grams of silica in the oxides,

C = grams of Zr0

2

, or g of ZrP

2 0

7 found X 0.4647, and

D = grams of sample used.

33
TITANIA BY THE HYDROGEN PEROXIDE (PHOTOMETRIC) METHOD

I. Scope

This method covers the determination of titania in

concentrations from 0.02 to 0.8 percent.

II. Principle of Method 19]

After separation of silica, hydrogen peroxide is added

to form a yellow complex with titanium in a sulfuric acid

solution. Spectrophotometric measurement is made at 410 nm.

III. Concentration Range

The recommended concentration range is from 0.15 to

3.0 mg of titanium per 100 ml of solution, using a 2-cm cell.

IV. Stability of Color

The color is stable for at least 1 hr.

V. Interferences

Interference from vanadium is negligible because of the

low concentration present in clays. Fluoride is reduced to

a noninterfering level by fuming with sulfuric acid.

VI. Reagents

(a) Hydrogen Peroxide Solution (H

2 O2 )-30 volume percent.

(b) Titanium, Standard Solution (A) (1 ml =< 1.0 mg Ti)

Dry lg of NBS SRM 154a, Titanium Oxide, at 105 °C for 2 hr

and cool. Transfer 0.8374g of the dried sample to a 250 ml

Erlenmeyer flask. Add lOg of (NH

4

) 2 S0

4 and 25 ml of H

2 S04

. Insert a short-stemmed glass funnel in the neck of the flask

and heat cautiously to boiling while rotating the flask over

an open flame. Continue the heating until solution is complete.

Cool and rapidly pour the solution into 4 00 ml of cool water,

while stirring. Rinse the flask 5 times with 10 ml portions

of H

2 S04 (1+1) , and transfer to a 500-ml volumetric flask.

Dilute to volume with H

2 S0

4 (1+9) , and mix.

(c) Titanium, Standard Solution (B) (1 ml ~ 0.1 mg Ti)

Using a pipet, transfer 20 ml of Solution (A) (1 ml * 1.0 mg

34
Ti) to a 200-ml volumetric flask, dilute to volume with

H

2 S0

4 (1+9) , and mix.

VII. Preparation of Calibration Curve

(a) Calibration Solutions. Using pipets , transfer 5,

10, 20, 25 and 30 ml of Solution (B) (1 ml * 0.1 mg Ti) to 100-ml volumetric flasks. Add 90 ml of H

2

SC> 4 (1+9) and 4 drops of ^2°2 Percent ) • Dilute to volume with H

2 S0

4 (1+9 ) , and mix.

(b) Reference Solution

Transfer 90 ml of H

2 S04 (1+9) to a 100-ml volumetric

flask, add 5 drops of H

2 02 (30 percent) , dilute to volume with

H

2 S04 (1+9) , and mix. Using this solution, adjust the

spectrophotometer to the initial setting, using a light

band centered at 410 nm. While maintaining this photometric

adjustment, take the photometric readings of the calibration

solutions using a 2-cm cell. Plot the photometric readings

of the calibration solutions against milligrams of titanium

per 100 ml of solution.

VIII. Procedure

(a) Transfer 2g of sample to a weighing bottle and dry

for 2 hrs at 140 °C. Transfer the sample to a platinum dish

containing a cover. Add 25 ml of water, 15 ml of H

2 S04

, 25 ml

of HN0

3 and 25 ml of HF and heat gently to dissolve the

sample. After dissolution, heat to fumes of H

2 S04

. Cool, and

cautiously add 100 ml of water. Transfer to a 500 ml volumetric flask, dilute to volume with water, and mix.

(b) Using a pipet, transfer a 50-ml aliquot to a 100 ml

volumetric flask. Add 15 ml of H

2 S0

4 (1+1) , dilute to volume with water, and mix.

(c) Transfer a portion of the solution to a 2-cm cell

and adjust the spectrophotometer to the initial setting

using a light band centered at 410 nm.

35
(d) Add 4 drops of ^2°2 ^® percent) to the solution

remaining in the flask, mix thoroughly, and measure the

absorbance or transmittance at 410 nm.

(e) From the calibration curve determine the number of

milligrams of titanium per 100 ml of solution.

IX. Calculation

Calculate the percentage of titania as follows:

m • ^ A X 1.668 Ti0

2

, percent =

b X 10 where

:

A = milligrams of titanium in 100 ml of the final

solution, and

B = grams of sample in 100 ml of the final solution.

36
IRON BY THE 1, 10-PHENANT HROLINE (PHOTOMETRIC) METHOD

I. Scope

This method covers the determination of iron oxide in

concentrations from 0.0 3 to 4 percent.

II. Principle of Method [10]

The sample is dissolved in mixed acids and fumed to remove silica and HF. The pH is adjusted to 5.5-6.0, and 1,10-

phenanthroline is added to form an orange-red complex with

ferrous iron. Spectrophotometric measurement is made at 510 nm.

III. Interferences

Copper, nickel and zinc form complexes and consume 1,10-

phenanthroline ; however, sufficient reagent is added to complex

the maximum amounts of these elements, in addition to the iron.

IV. Concentration Range

The recommended concentration range is 10 to 150 yg of

iron per 100 ml of solution, using a 2-cm cell.

V. Stability of Color

The color is stable for at least 2 hr.

VI. Reagents

(a) Citric Acid Solution (500g/l) . Dissolve 250g of

citric acid in 300 ml of water and dilute to 500 ml with

water.

(b) Hydroxylamine Hydrochloride Solution (100g/l) . Dissolve lOg of hydroxylamine hydrochloride (NH

2 0H.HC1) in

80 ml of water and dilute to 100 ml. Prepare fresh as needed.

(c) Iron, Standard Solution (A) (1 ml = 0.30 mg Fe)

.

Dissolve 150.4 mg of iron (NBS Standard 55E) in 50 ml of

HC1 (1+1). Heat gently to dissolve the iron. Cool, transfer

to a 500-ml volumetric flask, dilute to volume with water,

and mix.

(d) Iron, Standard Solution (B) (1 ml = 0.015 mg Fe)

.

Using a pipet, transfer a 25 ml aliquot of iron solution (A) to a 500-ml volumetric flask, dilute to volume with water,

and mix.

37
(e) 1, 10-Phenanthroline Solution (5g/l) . Dissolve

0.5g of 1 , 10-phenanthroline in 80 ml of hot water and dilute

to 100 ml with water. Prepare fresh as needed.

(f ) Sodium Acetate Solution (400g/l) . Dissolve 400g

of sodium acetate (NaC

2 H

3 02

. 3H

2 0) in 600 ml of water.

Dilute to 1 liter.

VII. Preparation of Calibration Curve

(a) Calibration Solutions.

(1) Transfer 0.0, 1, 3, 5 and 10 ml of iron

solution (B) (1 ml - 0.015 mg Fe) to six 150-ml beakers. Add

5 ml of citric acid solution and dilute to 50 ml with water.

(2) Add successively 2 ml of the 1 , 10-phenanthroline

solution, 2 ml of the hydroxylamine hydrochloride solution,

and 10 ml of the sodium acetate solution, mixing after

each addition. Adjust the pH to 5.5-6.0 with NH^OH (1+3).

Transfer the solution to a 100-ml volumetric flask, dilute

to approximately 9 5 ml with water and mix. Place the flask

in a water bath at about 70 °C for 30 min. Remove from the

bath, cool to room temperature, dilute to volume with water,

and mix.

(b) Spectrophotometry. Fill the reference cell with

water and adjust the spectrophotometer to the initial setting

using a light band centered at approximately 515 nm. While

maintaining this adjustment, take the photometric readings

of the calibration solutions using a 2-cm cell.

(c) Calibration Curve. Plot the net photometric

readings of the calibration solutions against milligrams of

iron per 100 ml of solution.

VIII. Procedure

(a) Using pipets, transfer a 10 ml aliquot from 500 ml

solution of SRM 97A, or a 4 ml aliquot from 500 ml

solution of SRM 98A prepared in Section VIII (a) , of

Titania by the Hydrogen Peroxide (Photometric) Method to

a 150-ml beaker. See page 35. Add 5 ml of citric acid

38
solution and dilute to about 50 ml. Proceed as directed in

Section VII (a) 2 and (b)

.

(b) From the value obtained, read from the calibration

curve the number of milligrams of iron present in 100 ml of

solution.

(c) Determine the blank correction by following the same procedure and using the same amounts of all reagents,

with the sample omitted.

IX. Calculation

Calculate the percentage of iron oxide as follows:

Pe

203

, percent = <» = l**^TM

where

:

A = milligrams of iron in 100 ml of the final solution,

B = milligrams of iron in 100 ml of the blank, and

C = grams of sample in 100 ml of the final solution.

39
IRON BY SnCl

2 - K

2 Cr

2 0

7 (VOLUMETRIC) METHOD

I. Scope

This method covers the determination of iron oxide

in concentrations from 0.03 to 4 percent.

II. Principle of Method 111]

The sample is fused with lithium metaborate and

leached in hydrochloric acid. Iron is reduced with SnCl

2 and titrated with a standard solution of K

2 Cr2 0^

.

III. Interferences

None of the elements present interfere.

IV. Apparatus

Graphite crucible (1 in. X 2.5 in.)

V. Reagents

(a) Mercuric Chloride Solution (saturated) . Dissolve

80g of HgCl

2 in 1 liter of hot water, stir and cool to room temperature

.

(b) Potassium Dichromate , Standard Solution (0.01N or 1 ml £ 0.5585 mg Fe) . Dissolve 0.4904g of K

2 Cr2 0

7 (SRM 136c) , in about 800 ml of water in a 1-liter

volumetric flask. Dilute to volume and mix. This is

a primary standard and the theoretical titer of

the solution can be used or it may be standardized

against high purity iron.

(c) Potassium Permanganate Solution (approximately

0.1N). Dissolve 0.32g of potassium permanganate (KMnO^

)

in 100 ml of water.

(d) Sodium Diphenylamine Sulfonate Indicator Solution (2g/l) . Dissolve 0.20g of sodium diphenylamine

sulfonate in 100 of water.

(e) Stannous Chloride Solution (50g/l) . Dissolve 5g

of SnCl

2 .2H

2 0 in 10 ml of HC1 and dilute to 100 ml with

water

.

(f) Sulfuric-Phosphoric Acid Mixture. Slowly add

150 ml of H

2 S04 to 500 ml of water, while stirring,

40
and cool to room temperature. Add 150 ml of H

3 P0

4 to the cool solution, dilute to 1 liter with water, and mix.

VI. Procedure

(a) Transfer approximately 0.25g of sample to a weighing bottle and dry for 2 hr at 14 0 °C. Stopper the

bottle and cool 1 hr in a desiccator. Lift the stopper

momentarily, replace, and weigh the bottle and sample.

Transfer the sample, without brushing, to a larger

weighing bottle containing 1.25g of lithium metaborate

and weigh the empty bottle.

(b) Mix the sample and lithium metaborate for 10 min.

Transfer to a graphite crucible. Dry wash the bottle with

small portion of lithium metaborate and transfer to the

crucible. Heat the crucible and contents in an electric

muffle furnace at 950 °C for 15 min. While stirring,

pour the hot fusion into 30 ml of HC1 (1+3) in a 250-ml

beaker. Cover the beaker and heat until the fusion is

dissolved.

(c) Cool and add 0 . IN KMnO^ solution dropwise

until a distinct pink color appears. Heat to boiling,

boil for 1 min to expel chlorine, add SnCl

2 solution,

drop by drop and with stirring, until the yellow color

of ferric chloride disappears. Add one drop in excess, but no more. Wash the wall of the beaker and quickly

cool the solution in an ice bath. Add at one stroke

10 ml of the saturated solution of mercuric chloride,

stir, and wash the wall of the beaker with cool water.

Allow to stand 2 to 5 min, with occasional stirring.

Add 100 ml of cool water, 20 ml of H

2 S0

4 -H

3 P0

4 mixture,

and 5 drops of sodium diphenylamine sulfonate indicator.

While stirring, titrate the iron with standard K

2 Cr

2 0

7 solution to a permanent reddish-violet color that

persists for 1 min.

(d) Make a blank determination, following the same procedure and using the same amounts of all reagents.

41
VII. Calculation

Calculate the percentage of iron oxide as follows:

Fe

2 0

3

, percent = (* - B) C X 0-05585 X 1.4298

x 10Q

where

A = milliliters of I^C^O.^ solution required to titrate

the sample,

B = milliliters of I^C^O^ solution required to titrate

the blank,

C = normality of the I^C^O^ solution, and

D = grams of sample used.

42
ZIRCONIA BY THE PYROCAT ECHOL VIOLET (PHOTOMETRIC) METHOD

I. Scope

This method covers the determination of zirconium in

concentrations from 0.005 to 0.5 percent.

II. Principle of Method 112, 13, 14]

Zirconium is extracted with trioctylphosphine oxide

(TOPO) , dissolved in cyclohexane, and forms a green complex

with pyrocatechol violet which is dissolved in absolute

alcohol. The photometric measurement is made at 655 nm.

III. Concentration Range

The recommended concentration range is from 4 to 40 yg

of zirconium per 25 ml of solution, using a 2 cm cell.

IV. Stability of Color

The color tends to fade on standing. Photometric measurements should be made within 30 min after the addition of the

pyrocatechol violet solution.

V. Interferences

Iron and titanium interfere but are removed by backwashing the TOPO extract with HNO-j. VI. Reagents

(a) Pyrocatechol Violet Solution. Dissolve 10 mg of

pyrocatechol violet in 20 ml of absolute ethyl alcohol.

(b) Trioctylphosphine Oxide (TOPO) (0.1 Molar).

Dissolve 3.86g of TOPO in 100 ml of cyclohexane.

(c) Zirconium Perchlorate, Standard Solution (A)

(1 ml * 1.0 mg Zr). Transfer 1.767g of ZrOCl

2 .8H

2 0 to a 300-ml Kjeldahl flask and dissolve in 25 ml of water. Add

40 ml of HC10

4 and evaporate to heavy fumes. Cool, add

100 ml of water, and mix. Transfer to a 500 ml volumetric

flask, dilute to volume with water, and mix.

(d) Zirconium Perchlorate, Standard Solution (B)

(1 ml * 4 yg Zr) . Transfer a 2.0 ml aliquot of zirconium

solution (A) to a 500-ml volumetric flask, and add 40 ml of

43
HCIO^ . Dilute to volume with water and mix. Prepare fresh

as needed.

VII. Preparation of Calibration Curve

(a) Transfer 0.0, 1, 2, 5, and 10-ml of zirconium

solution (B) (1 ml ^ 4 yg Zr) to five 60 ml separatory

funnels

.

(b) Dilute to 25 ml with HN0

3 (1+1). Add 5 ml of 0.1M

TOPO solution, stopper the funnel, and shake for 15 min on

a mechanical shaker. Allow the layers to separate and

discard the lower acid layer. Add 25 ml of HNO^ (1+1) and

shake for 15 min. Allow the layers to separate and discard

the acid layer.

(c) Using a pipet, transfer 2 ml of the TOPO extract to

a dry 25-ml volumetric flask. Add 10 ml of absolute alcohol,

and 1.5 ml of the pyrocatechol violet solution. Add 5 ml of

pyridine to neutralize any acid in the TOPO extract. Dilute

to volume with absolute alcohol, and mix.

(d) Fill the reference cell with water and adjust the

spectrophotometer to the initial setting using a light band

centered at 655 nm. While maintaining this adjustment, take

the photometric readings of the calibration solutions in a 2-cm cell within 3 0 min after addition of the pyrocatechol

violet solution.

(e) Plot the photometric readings of the calibration

solutions against micrograms of zirconium per 25 ml of

solution

.

VIII. Procedure

(a) Transfer 0 . lg of sample to a weighing bottle and

dry for 2 hrs at 14 0 °C. Cool, and weigh. Mix with 0.5g

of anhydrous lithium metaborate and transfer the mixture

to a graphite crucible. Heat the crucible and contents in an electric muffle furnace at 950 °C for 15 min. Swirl the

melt and transfer to a 400-ml beaker containing 50 ml of

44
HN0

3 (1+19) , while stirring. Transfer the solution to a 100 ml volumetric flask and wash with 47.5 ml of HNO^

(sp gr 1.42). Dilute to volume with water, and mix.

(b) Using a pipet, transfer a 20-ml aliquot of the

solution to a 60 ml separatory funnel and proceed as directed in Section VII, (b) through (d)

(c) From the value obtained, determine the micrograms

of zirconium present in 25 ml of solution.

IX. Calculation

Calculate the percentage of zirconia as follows:

„ _ AX 1.35

Z r09

, percent = 2—

Z B X 10

where

A = micrograms of zirconium in 25 ml of the final

test solution,

B = grams of sample in 25 ml of the final test

solution.

45
CHROMIUM OXIDE BY THE DIPHENYLCARBAZ IDE (PHOTOMETRIC)

METHOD

I. Scope

This method covers the determination of chromium oxide

in the range of 0.02 to 0.5 percent. The relative standard

deviation is 2 percent.

II. Principle of Method 115]

Chromium is oxidized to the sexivalent state with

ammonium peroxydisulfate and silver nitrate. A red-violet

complex is then formed with diphenylcarbazide . The photometric measurement is made at 54 0 nm.

III. Interferences

Iron interferes, but is removed with NaOH. Vanadium

in amounts present in clays does not interfere if the

solution is allowed to stand for 10 to 15 min after addition

of diphenylcarbazide.

IV. Stability of Color

The chromium diphenylcarbazide complex develops almost

immediately, but may fade after a short time. Spectrophotometric measurement should be made within 15 to 30 min after

addition of diphenylcarbazide.

V. Concentration Range

The recommended concentration range is 0.004 to 0.06 mg

of chromium in 100 ml of solution, using a 2-cm cell.

VI. Reagents

(a) Ammonium Peroxydisulfate Solution (100g/l)

.

Dissolve lOg of ammonium peroxydisulfate [(NH^)2S20g] in

90 ml of water. Prepare fresh as needed.

(b) Diphenylcarbazide Solution (0.32 percent). Dissolve

0.320g in 50 ml of ethyl acetate. Transfer the solution

to a 100-ml volumetric flask, dilute to volume with ethyl

acetate, and mix. Prepare fresh as needed.

(c) Potassium Dichromate , Standard Solution (A)

(1 ml - 1 mg Cr) . Dissolve 2.829g of K^r^^ (NBS

46
Standard 136c) in 500 ml of water contained in a 1-liter

volumetric flask. Dilute to volume with water, and mix.

(d) Potassium Dichromate, Standard Solution (B)

(1 ml 2 0.005 mg Cr) . Using a pipet, transfer a 10-ml

aliquot of chromium solution (A) to a 2-liter volumetric

flask, dilute to volume with water, and mix.

(e) Silver Nitrate Solution (2.5g/l). Dissolve

1.25g of AgN0

3 in 500 ml of water.

(f ) Sodium Hydroxide Solution (100g/l) . Dissolve 50g

of NaOH in 250 ml of water, cool, and dilute to 500 ml.

VII. Preparation of Calibration Curve

(a) Transfer 0.0, 1, 3, 5, 7, and 10 ml of chromium

solution (B) (1 ml ^ 0.005 mg Cr) to six 250-ml beakers

and add 4 ml of H

2 S0

4 (1+1)

.

(b) Dilute to about 50 ml with water. Add 10 ml of

AgNO^ solution and heat to boiling. Add 5 ml of ammonium

peroxydisulfate solution and boil for 25 min. Cool

rapidly and transfer to a 100-ml volumetric flask.

Dilute to about 90 ml with water and add 2 ml of diphenylcarbazide solution. Dilute to volume with water, and mix.

(c) Fill the reference cell with water and adjust

the spectrophotometer to the initial setting using a light band centered at 540 nm. While maintaining this

adjustment, take the photometric readings of the calibration solutions in a 2-cm cell within 15 to 30 min

after addition of the diphenylcarbazide solution.

(d) Plot the photometric readings of the calibration

solutions against milligrams of chromium per 100 ml of

solution.

VIII. Procedure

(a) Transfer slowly and with stirring, a 50-ml

aliquot from the 500 ml master solution prepared in

Section VIII (a) of the Titania by the Hydrogen-Peroxide

(Photometric) Method, see page 35, to 150 ml of NaOH

47
solution (10 percent) contained in a Teflon beaker or platinum dish. Digest on a steam bath for 1 hr and heat

to boiling. Allow the precipitate to settle, and filter

through a 11-cm medium filter paper previously washed

with NaOH (10 percent) . Wash the paper and precipitate 5 times with hot water. Using litmus paper as the indicator,

acidify the filtrate with H

2 S0

4 (1+1) and add 20 ml in excess, Evaporate the solution to about 80 ml, cool and transfer

to a 100-ml volumetric flask. Dilute to volume with

water, and mix.

(b) Using a pipet, transfer a 20-ml aliquot of the

solution to a 250-ml beaker and proceed as directed in

Section VII (b) and (c)

(c) From the value obtained, determine the milligrams

of chromium present in 100 ml of solution.

(d) Determine the blank correction by following the same procedure and using the same amounts of all reagents,

but with the sample omitted.

IX. Calculation

Calculate the percentage of chromium oxide as follows

Cr

203

, percent " »

x\l«TM

where

A = milligrams of chromium in 100 ml of the final

test solution,

B = milligrams of chromium in 100 ml of the blank,

and

C = grams of sample in 100 ml of the final test

solution

48
PART II ATOMIC ABSORPTION AND FLAME EMISSION SPECTROMETRY

The use of atomic absorption and flame emission

spectrometry as analytical techniques are firmly established.

Their applications to the determination of the alkali metals

such as lithium, sodium and potassium and to the determination of the alkaline-earth metals such as magnesium,

calcium, strontium and barium, all important constituents

of clay materials, are simple, rapid and reliable.

This section presents practical and well-established

spectrometric methods for the analyst and includes a procedure for dissolution of the sample, interferences,

reagents, preparation of calibration curves, and clear

stepwise directions for performing the analyses.

The instrumental system used in this work is outlined

and described in detail.

49
INST RUMENT AT ION

The instrumental system used in this work consists of

the following eight basic units, (1) a 0.5m monochromator

with exchangeable gratings having 1180 grooves per mm

o o blazed for 3000 and 7500 A and a dispersion of 1.6 A per mm

of slit width, (2) adjustable flame housing with a total

consumption nebulizer burner with 0£ - gases or premixed

air-acetylene and nitrous oxide-acetylene burner, (3) gas

flow meters and pressure regulators, (4) multiplier phototube (EMI 9558 AQ7) , (5) 0 to 2100 V multiplier phototube

power supply, (6) selective amplifier and synchronous

detector, (7) recorder, and (8) digital readout.

The atomic absorption instrument is similar to the

flame emission equipment except that the mechanical chopper

is placed between the hollow-cathode lamp and the nebulizer

burner

50
PROCEDURE FOR DISSOLUTION OF CLAY MATERIALS FOR FLAME

EMISSION AND ATOMIC ABSORPTION ANALYSES

1. Transfer 0.2g of sample, dried for 2 hr at 140 °C,

to a Teflon-lined pressure container 116]

.

2. Add 1 drop each of HC1 and HN0

3 and 4 ml of HF

.

3. Seal the container and place in an oven at 125 °C

for 2 hrs.

4. Remove from the oven, cool, open the container and

transfer the solution, to a platinum dish.

5. Add 5 ml of HF and 5 ml of HC10

4

. 6. Heat on a hot plate to dense fumes of HC10

4

. 7. Cool, add 1 ml of HC1 and 10 ml of H

2 0.

8. Warm the sample to dissolve the salts.

9. Cool and transfer the solution to a 25-ml

volumetric flask, dilute to volume and mix.

10. Transfer the solution to a plastic bottle for

subsequent use.

51
LITHIUM BY FLAME EMISSION SPECTROMETRY

I. Scope

This flame emission method is applicable to the

determination of 0.2 to lug of lithium per milliliter

of solution in clay materials. In this range, the

relative standard deviation of the method is 1 percent.

II. Principle of Method

Lithium is excited to emission in an oxygen-hydrogen

flame and is then determined by measuring the radiation

o intensity of the light emitted at a wavelength of 6708 A.

III. Interferences

o The resonance line of lithium at 6708 A is relatively

free of spectral line interferences. However, elements

such as sodium, calcium and strontium produce a continuum

or unresolved band structure in this region of the spectrum.

The CaO-CaOH and SrOH bands may cause an increase in flame

background. The magnitude of this interference will

depend upon the resolution of the monochromator . To make

the appropriate background correction it is necessary to scan the wavelength region of the lithium line.

IV. Reagents

(a) Lithium, Standard Solution A (1 ml - 1.000 mg Li).

Dry approximately 1 gram of reagent grade L^CO^ at 110 °C

for 2 hours. Cool in a desiccator. Transfer 0.5324 + 0.0002g of the dry Li

2 C0

3 to a 100-ml volumetric flask.

Add 60 ml of water and 3 ml of HC1 to dissolve the

Li^CO^ . Swirl the solution to expel C0

2

, dilute to volume

with water, and mix.

(b) Lithium, Standard Solution B (1 ml ^ 20 yg Li) . Using a pipet, transfer 2 ml of Solution A (1 ml a 1.000 mg

Li) to a 100-ml volumetric flask, dilute to volume with

water, and mix.

52
V. Preparation of Calibration Curve

1. Using pipets, transfer 1, 2, 3, 4 and 5 ml of

Solution B (1 il 2 20 yg Li) to 100 ml volumetric flasks,

dilute to volume with water, and mix.

2. Turn on the operating switches of the flame

emission spectrometer.

3. Set the voltage to the multiplier phototube at

1000 v.

4 . Install the total consumption burner in the

flame housing.

5. Open the valves to the oxidant (oxygen) and fuel

(hydrogen) cylinders and set the tank regulators at

30 and 20 psi, respectively.

6. Ignite the burner and adjust the pressure and/or

flow rates recommended by the manufacturer.

7. Set the wavelength dial of the monochromator to

o 6807 A and the slit width at 50 y . 8. Aspirate the lithium solution with the highest

concentration (1 ml s 1 yg Li) from the series prepared

in Step 1.

9. Adjust the gain of the operational amplifier to give 85 percent of full scale, as indicated on the recorder.

10. While aspirating, set the wavelength dial of the

o monochromator at 6804 A and scan the lithium line at

o o 6807 A at a rate of 10 A/min.

11. Repeat step 10 with each calibration solution,

in turn, and record its radiation intensity. Aspirate

water between each standard solution and record the

radiation intensity.

12. Plot the radiation intensity values, corrected for

background, against micrograms of lithium per milliliter on rectangular coordinate paper.

53
VI. Procedure

1. Transfer to two 25-ml volumetric flasks, A and B,

two equal test portions containing 10 to 15 yg of lithium.

2. Dilute test portion A to volume with water and

mix

3. To test portion B, add 5 yg of lithium, dilute to, volume with water, and mix.

4. Aspirate test portions A and B, and measure the

radiation intensity of each. Aspirate water after each test

portion

5. From the calibration curve, determine the lithium

concentration as yg/ml.

6. Subtract the concentration, yg/ml, that was added

to test portion B. If the concentrations of the two test

portions agree, proceed to step 7. If the recoveries

do not agree , correct by the standard addition method

(Note 1) and proceed to step 7.

7. Calculate the percent lithium as follows:

T

. A . , . ^ CXZX 2 .1528 Li~0, weight percent = j W X io 4 where

C = lithium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, grams.

Note 1 - See, Menis , 0. and Rains, T. C. Sensitivity,

Detection Limits, Precision and Accuracy in Flame Emission

and Atomic Absorption Spectrometry. Chapter II pp 47-77 in

Analytical Flame Spectroscopy—Selected Topics.

Radu Mavrodineanu, Editor. MacMillan and Co. Ltd. (1970),

New York

54
SODIUM BY FLAME EMISSION SPECTROMETRY

I. Scope

This flame emission method is applicable to the

determination of 1 to 5 yg of sodium per milliliter of

solution in clay materials. In this range, the relative

standard deviation of the method is 1 percent.

II. Principle of Method

Sodium is excited to emission in an oxygen-hydrogen

flame and is then determined by measuring the radiation

o intensity of the light emitted at a wavelength of 5890 A. III. Interferences

o The resonance line of sodium at 5890 A shows very little

spectral interference from other elements. Because of the

high sensitivity of sodium emission, the flame background,

due to a continuum or unresolved band structure, is very

small when the resolution of the monochromator is better

o than 1 A. The major sources of errors are from the

contamination of sodium during the preparation of the sample,

and from air-borne dust particles during the flame emission

measurements. Extreme care must be taken in handling the

sample and disposable or clean gloves must be worn at all

times

.

IV. Reagents

(a) Sodium, Standard Solution A (1 ml * 10.0 mg Na)

.

Dry approximately 5 grams of reagent grade NaCl at

110 °C for 2 hrs. Cool in a desiccator. Transfer 2.542 + O.OOlg of the dry NaCl to a 100-ml volumetric flask,

dissolve in 50 ml of water and then add 10 ml of ultra pure

IN HC1. Dilute to volume with water, and mix.

(b) Sodium, Standard Solution B (1 ml - 100 yg Na)

.

Using a pipet, transfer 1 ml of Solution A (1 ml a 10.0 mg

Na) to a 100-ml volumetric flask, dilute to volume with

water, and mix.

55
V. Preparation of Calibration Curve

1. Using pipets , transfer 1, 2, 3, 4 and 5 ml of

Solution B (1 ml ^ 100 yg Na) to 100-ml volumetric flasks,

dilute to volume with water, and mix.

2-6. Proceed as directed in steps 2 to 6 of Section V

of the procedure for lithium. See page 53.

7 . Set the wavelength dial of the monochromator to 5890 A and slit width at 50 y

8 . Aspirate the sodium solution with the highest

concentration (1 ml =^ 5 y g Na) from the series prepared

in Step 1.

9. Adjust the gain of the operational amplifier

to give 85 percent of full scale, as indicated on the

recorder

10. While aspirating, set the wavelength dial of the

o o monochromator at 5885 A and scan the sodium line at 5890 A

o at a rate of 10 A/min.

11. Repeat step 10 with each calibration solution,

in turn, and record the radiation intensity. Aspirate water

between each standard solution and record the radiation

intensity.

12. Plot data as directed in step 12 of the procedure

for lithium. See page 53.

VI. Procedure

1. Transfer to two 25-ml volumetric flasks, A and B,

two equal test portions containing 25 to 50 y g of sodium.

2 . Dilute test portion A to volume with water and

mix.

3. To test portion B, add 25 yg of sodium, dilute

to volume with water and mix.

4-6. Proceed as directed in steps 4 to 6 of Section VI of the procedure for lithium. See page 54.

7. Calculate the percent sodium as follows:

56
xt a • v.. a. C X Z X 1.348 Na 9 0, weight percent = —

j

' W X 10

where

:

C = sodium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, grams.

57
POTASSIUM BY FLAME EMISSION SPECTROMETRY

I. Scope

This flame emission method is applicable to the determination of 2 to 10 yg of potassium per milliliter of

solution in clay materials. In this range, the relative

standard deviation of the method is 1 percent.

II. Principle of Method

Potassium is excited to emission in an oxygen-hydrogen

flame and is then determined by measuring the radiation

o intensity of the light emitted at a wavelength of 7665 A.

III. Interferences

o The potassium doublet at 7665 and 7699 A suffers

seriously from the spectral interference of rubidium which

o emits strongly at 7800 A. To overcome this interference,

it is necessary to have an instrument with good dispersion

and resolution. Another source of interference results

from the enhancement of the emission of potassium when

rubidium or cesium are present. This is due to the

repression of the ionization of potassium by electrons

produced by these elements in the flame. This enhancement

can be corrected by means of the standard addition method.

IV. Reagents

(a) Potassium Standard Solution A (1 ml - 10.0 mg K)

Dry approximately 2 grams of reagent grade KC1 at 110 °C

for 2 hrs. Cool in a desiccator. Transfer 1.907 + O.OOlg of the dry KC1 to a 100-ml volumetric flask,

dissolve in 50 ml of water and then add 10 ml of ultra pure

IN HC1 . Dilute to volume with water, and mix.

(b) Potassium, Standard Solution B (1 ml - 100 yg K) . Using a pipet, transfer 1 ml of Solution A (1 ml - 10.0 mg K) to a 100-ml volumetric flask, dilute to volume with water,

and mix.

58
V. Preparation of Calibration Curve

1. Using pipets , transfer 2 t 4, 6, 8 and 10 ml of

Solution B (1 ml - 100 yg K) to 100 ml volumetric flasks,

dilute to volume with water and mix.

2-6. Proceed as directed in steps 2 to 6 of Section V

of the procedure for lithium. See page 53.

7. Set the wavelength dial of the monochromator to 7665 A and the slit width at 50 y.

8. Aspirate the potassium solution with the highest

concentration (1 ml - 10 yg K) from the series prepared

in Step 1.

9. Adjust the gain of the operational amplifier to give 85 percent of full scale, as indicated on the recorder.

10. While aspirating, set the wavelength dial of the

0 monochromator at 76 60 A and scan the potassium line at

o o 7665 A at a rate of 10 A/min.

11. Repeat step 10 with each calibration solution, in

turn, and record its radiation intensity. Aspirate water

between each standard solution and record the radiation

intensity.

12. Plot data as directed in step 12 of the procedure

for lithium. See page 53.

VI. Procedure

1. Transfer to two 25-ml volumetric flasks, A and B, two equal test portions containing 50 to 100 yg of potassium.

2 . Dilute test portion A to volume with water and

mix.

3. To test portion B, add 50 yg of potassium, dilute

to volume with water and mix.

4-6. Proceed as directed in steps 4 to 6 of Section VI

of the procedure for lithium. See page 54.

7. Calculate the percent potassium as follows:

K 0, weight percent =

C X Z X ]' 205

W X 10

59
where

C = potassium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, gram.

60
MAGNESIUM BY ATOMIC ABSORPTION SPECTROMETRY

I. Scope

This atomic absorption method is applicable to the

determination of 0.4 to 2.4 yg of magnesium per milliliter

of solution in clay materials. In this range, the relative

standard deviation of the method is 2 percent.

II. Principle of Method

In atomic absorption spectrometry, the analyte of the

test portion is converted to an atomic vapor, and the

absorption of light by the ground state atoms in the vapor

phase is measured at the specific wavelength which is

characteristic of the element. The light source is

generally a hollow-cathode lamp adjusted to give an intense

and sharp resonance line. Many parameters affect the

production of atoms in flame gases. For many elements, the

number of ground state resonance atoms will depend not only

on the temperature of the flame, but on whether the fuel

mixture results in a reducing or oxidizing flame. The

concentration of free atoms often varies with the height of

observation above the burner tip.

III. Interferences

The interferences in atomic absorption spectrometry

are spectral, physical and chemical in nature. Usually

spectral interferences are associated with the source of

radiation—the hollow-cathode lamp. The filler gas in a hollow-cathode lamp, as well as impurities in the cathode

material, will emit its characteristic radiation which may

interfere with the analytical line. Spectral interferences

from the source can be controlled by determining the

constituents within the lamp and by selecting the proper

optical condition to minimize or eliminate this interference.

Physical interferences may alter processes within

the flame gases. These include aspiration, nebulization,

solvent evaporation and vaporization. By selecting the

61
proper oxidant-fuel gas and burner system, these types of

interferences can be minimized.

The greatest number of interferences in atomic

absorption are of a chemical nature. Chemical interferences

affect the analyte and may occur in the vapor, solid or liquid phase within the flame , Reactions occurring in the

vapor phase may suppress or enhance the dissociation of

the molecular species into atomic vapor. This is referred

to as the condensed—phase interference. To control this

type of interference, the oxidant-fuel and nebulizer-burner

system must be carefully regulated. To overcome condensed

phase types of interference, protective chelating agents

can be used. Another approach for minimizing these

interferences is by using high temperature flames such as the nitrous oxide-acetylene fixture; however, high

temperature flames produce excessive ionization, which is

undesirable. Chemical interferences can be overcome most

satisfactorily by premixing the oxidant, air-nitrous

oxide, in the proper ratio to provide the proper flame

temperature

IV. Reagents

(a) Magnesium, Standard Solution A (1 ml ^ 10.0 mg Mg)

Transfer 1.0000 + 0.0005g of high purity magnesium metal

to a 150-ml beaker. Add 50 ml of water. Slowly add

6 ml of HC1 . After dissolution of the sample, transfer

to a 100-ml volumetric flask, dilute to volume with water

and mix.

(b) Magnesium, Standard Solution B (1 ml a 40 yg Mg) . Using a pipet, transfer 1 ml of Solution A (1 ml =; 10.0 mg

Mg) to a 250-ml volumetric flask, dilute to volume with

0. 1M HC1 , and mix

(c) Lanthanum, Standard Solution (1 ml = 10.0 mg La).

Transfer 11.73g of La

2

0

3 to a 100-ml beaker. While

stirring, add 20 ml of HC1 and heat to dissolve. Cool, add

62
90 ml of HC10

4 and heat to fumes. Cool, transfer to a 1-

liter volumetric flask, dilute to volume with water, and mix.

(d) Glycerol Solution (50 v/v percent, alkaline-earth

free). Transfer 500 ml of analytical-reagent grade

glycerol to a 1-liter volumetric flask and dilute to volume with water. Prepare an ion-exchange resin column

by mixing an equal weight of Dowex 50-X8 (50 to 100 mesh)

and Dowex 1-X10 (50 to 100 mesh) in a beaker. Wash with 6M

HC1 and then with water. Transfer the resin to a 1 x 15-cm

glass column to provide a bed 10 cm in depth. Pass the

glycerol solution through the column and collect for

subsequent use.

V. Preparation of Calibration Curve

1. Using pipets , transfer 0, 1, 2, 3, 4 and 5 ml of

Solution B (1 ml ~ 40 p.g Mg) to 100-ml volumetric flasks

and dilute to about 50 ml with water.

2. To each solution, add 10 ml of the standard

solution of lanthanum and 20 ml of the purified glycerol

solution.

3. Dilute the flasks to volume with water, and mix.

The solutions will contain 1000 yg of lanthanum/ml in 0 . IN HC10

4 and 10 percent glycerol.

4. Install the magnesium hollow-cathode lamp in the

atomic absorption instrument.

5. Set the current at two-thirds of the maximum

operating current.

6. Turn on the operating switches of the atomic

absorption instrument and allow the hollow-cathode lamp to warm up for 15 min.

7. Set the slit width at 50 u and the voltage to the multiplier phototube (R-106) at 500 V.

8. Install the premixed-laminar flow burner equipped

with a 10-cm head within the flame housing.

63
9. Open the valves to the oxidant (air) and fuel

(acetylene) cylinders and set the tank regulators at

40 and 15 psi, respectively.

10. Align the burner within the optical path of the

light source.

11. Ignite the burner and adjust the pressure and/or

flow rates to produce a reducing flame. Note . Observe the

manufacturer's safety precautions in lighting the premixed

burner.

12. Adjust the wavelength dial of the monochromator to Aspirate water between each standard and record the

absorbance

13. Adjust the gain of the operational amplifier to 100 percent transmission and the dark current to zero.

14. Aspirate the magnesium solution with the highest

concentration (1 ml = 2 yg Mg) from the series prepared

in Step 1 and adjust the height and alignment to give the

maximum absorbance.

15. Aspirate each calibration solution, in turn,

including the reagent blank, and record the absorbance.

Aspirate water between each standard and record the

absorbance

16 . Plot the absorbance values , corrected for reagent

blanks, etc. against micrograms of magnesium per milliliter,

on rectangular coordinate paper. (The calibration curve should pass through the origin, but may deviate at higher

concentrations of the analyte.)

VI. Procedure

1. Transfer to two 10-ml volumetric flasks, A and B,

two equal test portions containing 4 to 12 yg of magnesium.

2. To test portion A, add 1 ml of the standard

solution of lanthanum (1 ml ~ 10 mg La) , 2 ml of glycerol,

dilute to volume with water, and mix.

64
3. To test portion B, add 4 yg of magnesium, 1 ml of

the standard solution of lanthanum (1 ml ~ 10 mg La) , 2 ml

of glycerol, dilute to volume with water, and mix.

4. Aspirate test portions, A and B, and measure the

absorbance of each.

5. From the calibration curve, determine the magnesium

concentrations, yg/ml.

6. Recheck the calibration curve with standard

solutions of magnesium.

7. Subtract the concentration, yg/ml, that was

added to test portion B. If the concentrations of the

two test portions agree, proceed to step 8. If the

recoveries do not agree, correct by the standard addition

method, and proceed to step 8.

8. Calculate the percent magnesium as follows:

MgO, weight percent =

C X_ Z X 1.658

W X 10 4 where

:

W

Zc magnesium concentration, yg/ml

dilution factor

test portion of solid sample, grams.

65
CALCIUM BY ATOMIC ABSORPTION SPECTROMETRY

I Scope

This atomic absorption method is applicable to the

determination of 0.2 to 1.0 yg of calcium per milliliter of

solution in clay materials. In this range, the relative

standard deviation of the method is 2 percent.

II. Principle of Method

See Section II of Magnesium Method.

III. Interferences

See Section III of Magnesium Method.

IV. Reagents

(a) Calcium, Standard Solution A (1 ml * 10.0 mg Ca)

Dry approximately 3 grams of CaC0

3 (NBS-915) at 110 °C

for 2 hrs. Cool in a desiccator. Transfer 2.497 + O.OOlg of the dry CaC0

3 to a 100-ml volumetric flask.

Slowly add 55 ml of ultra pure 1M HC1 and warm to dissolve.

Swirl the solution to expel C0

2

, dilute to volume with

0.1M HC1, and mix.

(b) Calcium, Standard Solution B (1 ml ~ 20 yg Ca)

Using a pipet, transfer 1 ml of Solution A (1 ml ~ 10.0 mg

Ca) to a 50 0-ml volumetric flask, dilute to volume with

0 . 1M HC1 , and mix.

(c) Aluminum, Standard Solution (1 ml =j 10.0 mg Al) . Transfer 5.0 grams of aluminum metal (NBS 44e) to a 400-ml

beaker. Add 50 ml of water and 4 0 ml of HC1 . Warm to dissolve, cool, transfer to a 500-ml volumetric flask.

Dilute to volume with water, and mix.

(d) Potassium, Standard Solution (1 ml ^10.0 mg K)

Transfer 9.5 grams of KC1 to a 500-ml volumetric flask.

Add 200 ml of water and 10 ml of 1M HC1. Dilute to volume

with water, and mix.

V. Preparation of Calibration Curve

1. Using pipets , transfer 0, 1, 2, 3, 4 and 5 ml of

Solution B (1 ml * 20 yg Ca) t© 100-ml volumetric flasks,

and dilute to about 50 ml with water.

66
2. To each flask, add 5 ml of the standard solution of

potassium and 5 ml of the standard solution of aluminum.

3. Dilute to volume with water, and mix. The solutions

will contain 500 yg of potassium and aluminum/ml.

4 . Install the calcium hollow-cathode lamp in the

atomic absorption instrument.

5-7. Proceed as directed in steps 5 to 7 of Section V

of the Magnesium Method. See page 63.

8 . Install the premixed-laminar flow burner equipped

with a 5-cm head O^O) in the flame housing.

9-10. Proceed as directed in steps 9 and 10 of Section V

of the Magnesium Method.

11. Ignite the air-acetylene burner and adjust the flame

to fuel rich conditions by gradually introducing £<2^2 ' T ^en introduce ^0 and ^2^2 un^^- ^he ratio to air is 80-20.

Note . Observe the manufacturer's safety precautions in the use of the nitrous oxide-acetylene flame

.

12. Adjust the wavelength dial of the monochromator to the

o resonance line of calcium at 4227 A to yield a maximum

reading.

13. Proceed as directed in steps 13 to 16 of Section V

of the Magnesium Method. See page 64.

VI. Procedure

1. Transfer to two 25-ml volumetric flasks, A and B,

two equal test portions containing 5 to 15 yg of calcium.

2. Dilute test portion A to volume with water and mix.

3. To test portion B, add 8 yg of calcium, dilute to volume with water, and mix.

4. Aspirate test portions, A and B, and measure the

absorbance of each.

5. From the calibration curve, determine the calcium

concentration, yg/ml.

67
6 . Recheck the calibration curve with standard solutions

of calcium.

7. Subtract the concentration, yg/ml, that was added

to test portion B. If the concentrations of the two test

portions A and B agree, proceed to step 8. If the

recoveries do not agree, correct by the standard addition

method, and proceed to step 8. 8. Calculate the percent calcium as follows:

CaO, weight percent =

C X Z X 1

! 399

W X 10 where

C = calcium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, grams.

68
STRONTIUM BY ATOMIC ABSORPTION SPECTROMETRY

I.' Scope

This atomic absorption method is applicable to the

determination of 1 to 5 y g of strontium per milliliter of

solution in clay materials. In this range, the relative

standard deviation of the method is 2 percent.

II. Principle of Method

See Section II of Magnesium Method.

III. Interferences

See Section III of Magnesium Method.

IV. Reagents

(a) Strontium, Standard Solution A (1 ml =; 10.0 mg Sr) . Dry approximately 2 grams of reagent grade SrC0

3 at

110 °C for 2 hrs. Cool in a desiccator. Transfer 1.685 + O.OOlg of the dry SrC0

3 to a 100 ml volumetric flask.

Slowly add 50 ml of ultra pure 1M HC1 and warm to dissolve.

Swirl the solution to expel C0

2

, dilute to volume with 0.1M

HC1, and mix.

(b) Strontium, Standard Solution B (1 ml a 100 yg Sr) . Using a pipet, transfer 1 ml of Solution A (1 ml a 10.0 mg Sr) to a 100-ml volumetric flask, dilute to volume with 0.1M HC1,

and mix.

(c) Aluminum, Standard Solution (1 ml ^ 10.0 mg Al)

.

Proceed as directed in Section IV of Calcium Method. See page 66.

(d) Potassium, Standard Solution (1 ml = 10.0 mg K)

.

Proceed as directed in Section IV of Calcium Method. See page 66.

V. Preparation of Calibration Curve

1. Using pipets, transfer 0, 1, 2, 3, 4 and 5 ml of

Solution B (1 ml 100 yg Sr) to 100-ml volumetric

flasks, and dilute to about 50 ml with water.

2. To each flask, add 5 ml of the standard solution

of potassium and 5 ml of the standard solution of aluminum.

3. Dilute to volume with water, and mix. The solutions

will contain 500 yg of potassium and aluminum/ml.

69
4 . Install the strontium hollow-cathode lamp in the

atomic absorption instrument.

5-7 . Proceed as directed in steps 5 to 7 of Section V of

the Magnesium Method. See page 63.

8 . Install the premixed-laminar flow burner equipped

with a 5-cm head (N 2 0) ^n the flame housing.

9-10. Proceed as directed in Steps 9 to 10 of Section V of

the Magnesium Method. See page 64. 11. Ignite the air-acetylene burner and adjust the flame

to fuel rich conditions by gradually introducing C

2 H2

. Then

introduce N

2 0 and C

2 H

2 until the N

2 0 ratio to air is 80-20.

Note. Observe the manufacturers safety precautions in the use of the nitrous oxide-acetylene flame.

12. Adjust the wavelength dial of the monochromator to

o the resonance line of strontium at 460 7 A to yield a maximum reading.

13. Proceed as directed in Steps 13 to 16 of Section V

of the Magnesium Method. See page 64.

VI. Procedure

1. Transfer to two 25-ml volumetric flasks, A and B,

two equal test portions containing 25 to 50 yg of strontium.

2. Dilute test portion A to volume with water and mix.

3. To test portion B, add 25 y g of strontium, dilute

to volume with water , and mix

4. Aspirate test portions, A and B, and measure the

absorbance of each.

5. From the calibration curve, determine the strontium

concentrations, yg/ml.

6. Recheck the calibration curve with standard

solutions of strontium.

7. Subtract the concentration, yg/ml, that was added

to test portion B. If the concentrations of the two test

portions agree, proceed to step 8. If the recoveries do not

agree, correct by the standard addition method, and proceed

to step 8

70
8 . Calculate the percent strontium as follows

SrO, weight percent =

C X 2 X *' 183

W X 10

4 where

:

C = strontium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, grams.

71
BARIUM BY FLAME EMISSION SPECTROMETRY

I. Scope

This flame emission method is applicable to the

determination of 0.5 to 2.5 yg of barium per milliliter of

solution in clay materials. In this range, the relative

standard deviation of the method is 2 percent.

II. Principle of Method

Barium is excited to emission in a nitrous oxide, air

(80-20) -acetylene flame and is then determined by measuring

the radiation intensity of the light emitted at a wavelength

of 5536 A.

III. Interferences

o The resonance line of barium at 5536 A suffers from

serious spectral interference of the CaO-CaOH band system

when a low temperature flame is used. Using a high

temperature flame such as nitrous oxide-acetylene, the

interference is minimized. The magnitude of the interference

will depend upon the resolution of the monochromator

IV. Reagents

(a) Barium, Standard Solution A (1 ml ~ 10.0 mg Ba)

Dry 2 grams of reagent grade BaC0

3 at 110 °C for 2 hrs

Cool in a desiccator. Transfer 1.437g + O.OOlg of

the dry BaC0

3 to 100-ml volumetric flask. Add 40 ml of

1M HC1 and warm to dissolve. Swirl the solution to expel

C0

2

, dilute to volume with 0.1M HC1, and mix.

(b) Barium, Standard Solution B (1 ml * 50 yg Ba) . Using a pipet, transfer 1 ml of Solution A (1 ml ^ 10.0 mg Ba) to a 200-ml volumetric flask, dilute to volume with 0.1M HC1,

and mix.

(c) Aluminum, Standard Solution (1 ml =; 10.0 mg Al) . Prepare as directed in Section IV of the Calcium Method.

See page 66.

(d) Potassium, Standard Solution (1 ml * 10.0 mg K)

Prepare as directed in Section IV of the Calcium Method.

See page 66.
V. Preparation of Calibration Curve

1. Using pipets, transfer 0, 1, 2, 3, 4 and 5 ml of

Barium Solution B (1 ml - 50 yg Ba) to 100 ml volumetric

flasks, and dilute to about 50 ml with water.

2. To each flask, add 5 ml of the standard solution of

potassium and 5 ml of the standard solution of aluminum.

3. Dilute to volume with water, and mix.

4. Turn on the operating switches of the flame emission

spectrometer.

5. Set the voltage to the multiplier phototube at 1400 V.

6. Install the premixed laminar flow burner equipped

with a 5-cm head (N 2 °) in the flame housing.

7. Ignite the air-acetylene burner and adjust the flame

to fuel rich conditions by gradually introducing C

2 H2

. Then

introduce N

2 0 and C^H^ until the N2 0 ratio to air is 80-20.

Note. Observe the manufacturer's safety precautions in the use of the nitrous oxide-acetylene flame.

o 8. Set the wavelength of the monochromator to 5536 A

and the slit width at 50 u . 9 . Aspirate the barium solution with the highest con- centration (1 ml - 2.5 yg Ba) from the series prepared in

step 1. 10. Adjust the gain of the operational amplifier to give 85 percent of full scale, as indicated on the recorder.

11. While aspirating set the wavelength of the mono-

° ° chromator at 5530 A and scan the barium line at 5536 A

o at a rate of 10 A/min.

12. Repeat step 10 with each calibration solution, in

turn, and record its radiation intensity. Aspirate water

between each standard solution and record the radiation

intensity.

13. Plot the radiation intensity values, corrected for

background, against micrograms of barium per milliliter, on rectangular coordinate paper.

73
VI. Procedure

1. Transfer to two 25 -ml volumetric flasks, A and B,

two equal test portions containing 15 to 30 yg of barium.

2. Dilute test portion A to about 15 ml with water,

add 1 ml of standard solution of potassium, dilute to volume

with water and mix.

3. To test portion B, add 15 yg of barium, 1 ml of

standard solution of potassium, dilute to volume with water

and mix.

4. Aspirate test portions, A and B, and measure the

radiation intensity of each.

5. From the calibration curve, determine the barium

concentrations, yg/ml.

6 . Recheck the calibration curve with standard

solutions of barium.

7. Subtract the concentration, yg/ml, that was added

to test portion B. If the concentrations of the two test

portions agree, proceed to step 8. If the recoveries do

not agree correct by the standard addition method, and

proceed to step 8

8. Calculate the percent barium as follows:

BaO, weight percent =

C X Z X 1 ' 117

W X 10 4 where

C = barium concentration, yg/ml

Z = dilution factor

W = test portion of solid sample, grams.

The authors are particularly appreciative of the

valuable assistance of Mrs. Mary Pantazis in typing and

assembling this report and of Mrs. Rosemary Maddock who

provided overall coordination and editorial assistance.

74
REFERENCES

[1] Lundell, G. E. F. and Hoffman, J. I., NBS J. Res. 1,

90 (1928) RP 5.

[2] Flanagan, F. J., U. S. Geol. Survey, Giochim et Cosmochim Acta 33., 81-120 (1969) . [3] Peck, L. C., U. S. Geol. Survey Bulletin 1170 , 21 (1964).

[4] Bell, R. K., NBS Misc. Publ . 260-7, 82 (1965).

[5] Hillebrand, W. F. , Lundell, G. E. F., Bright, H. A. and

Hoffman, J. I., Applied Inorganic Analysis, 2nd ed. 507

(1953), John Wiley & Sons, New York.

[6] Hague, J. L. and Bright, H. A., Colorimetric Determination of Phosphorus in Steel and Iron, J. Res. Nat. Bur. Std. 2_6, A05 (1941) RP 1386.

[7] Suher, N. H. and Ingamells, C. 0., Solution Technique for

Analysis of Silicates, Anal. Chem. 3_8, 6, 730 (1966).

[8] Govindaraju, K. , Ion Exchange Dissolution Method for

Silicate Analysis, Anal. Chem. 4_0 , 24 (1968).

[9] ASTM Chemical Analysis of Metals; Sampling and Analysis

of Metal Bearing Ores, Part 32, p. 158 (1971).

[10] ibid p. 144.

[11] Lundell, G. E. F., Hoffman, J. I. and Bright, H. A.,

Chemical Analysis of Iron and Steel, p. 532 (1931)

,

John Wiley & Sons, New York.

[12] Young, J. P., French, J. R. and White, J. C, Anal.

Chem. 30_, 422 (1958) . [13] Young, J. P. and White, J. C, Talanta 1, 263 (1958).

[14] Wood, D. F. and Jones, J. T. , The Analyst 9_0, 1068

(1965) . [15] ASTM Chemical Analysis of Metals; Sampling and Analysis

of Metal Bearing Ores, Part 32, p. 137 (1971).

[16] Bernas, B., Anal. Chem. 40_, 1682 (1968).

75
S. Departi^|s# of Commerce

MauriceSIL Stans

APPENDIX 1

Certificate of &nalpgfe

STANDARD REFERENCE MATERIAL 97 a Flint Clay

(Results based on sample dried for two hours at 140 °C)

Analyst Si02 Al 2 Oa Fe20, Ti02 P2 05 K20 Na20 Li 20 Zr02 BaO MgO CaO SrO Cr2Os

Loss on

Igni- tion

H'l 43.74 38.65 {":£} {SC} 0.34 0.53= 0.033' 0.12" 0.063' 0.078* 0.16* O.lle 0.17k 0.028h 13.32

21*1 43.68 38.95 .45 1.95 .35 .51" Ml' .10* .07 .14* .11* .18* .03 13.31

3 43.60 38.79 .43° 1.87d .38 ! .46" Average.. 43.67 38.79 0.45 1.90 0.36 0.50 0.037 0.11 0.075

0.15 0.11 0.18 0.03 13.32 References: [1] G.E.F. Lundell and J.I. Hoffman, NBS J. Res. 1, 91 (1928) RP5.

[2] L. C. Peck, Geological Survey Bulletin 1170, (1964). "o-phenanthroline photometric method.

b Iron reduced with SnCl : and titrated with standard potas- sium dichromate solution. "Cupferron gravimetric method.

'H202 photometric method.

e Flame emission spectrometric method.

'Pyrocatechol violet photometric method. "Atomic absorption method.

h Diphenylcarbazide photometric method. 'Molybdenum-blue photometric method. List of Analysts

R. K. Bell, B. B. Bendigo, T. C. Rains, T. A. Rush,

E. R. Deardorff, J. R. Baldwin, R. A. Paulson, W. P. Schmidt, and S. D. Rasberry, Analytical Chemistry Division, Institute for Materials Research, National Bureau of Standards.

2. L. C. Peck, United States Geological Survey, Denver, Colorado.

3. L. M. Melnick, J. D. Selvaggio, and D. G. Cunningham, Applied Research Laboratory, United

States Steel Corporation, Pittsburgh, Pennsylvania. The material for the preparation of this standard was proyided by the A. P. Green Fire Brick Company,

Mexico, Missouri. The overall direction and coordination of the technical measurements leading to certification were performed under the chairmanships of O. Menis and J. I. Shultz. The technical and support aspects involved in the preparation, certification and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials by J. L. Hague.

Washington, D. C. 20234 J- Paul Cali, Acting Chief October 8, 1969 Office of Standard Reference Materials 76
S. DepartrrfenJ? of Commerce

Maurice^H. Stans

APPENDIX 2

Certificate of gfaalpsfe

STANDARD REFERENCE MATERIAL 98 a Plastic Clay

(Results based on sample dried for two hours at 140 °C)

Analyst Si02 A1 203 Fe20, Ti02 P205 K20 Na20 Li 20 Zr02 BaO MgO CaO SrO Cr20,

Loss on

Igni- tion

H'l 48.98 33.13 {i:!?"}

fl.56«\ \1.63d

/ 0.11 1.07" 0.080° 0.075" 0.042' 0.031" 0.42« 0.31« 0.041* 0.030h 12.40 2 m 48.91 33.31 1.35 1.64 .10 1.08" .083* .064* .03 .43" .31" .037* .04 12.49 3 33.12 1.28" 1.61* .IV 0.98' Average.

48.94 33.19 1.34 1.61 0.11 1.04 0.082 0.070 0.03 0.42 0.31 0.039 0.03 12.44 References: [1] G.E.F. Lundell and J.I. Hoffman, NBS J. Res. 1, 91 (1928) RP5.

[2] L.C. Peck, Geological Survey Bulletin 1170, (1964). "o-phenanthroline photometric method.

bIron reduced with SnCl2 and titrated with standard potas- sium dichromate solution. "Cupferron gravimetric method.

dH202 photometric method.

"Flame emission spectrometry method.

'Pyrocatechol violet photometric method. "Atomic absorption method.

h Diphenylcarbazide photometric method. 'Molybdenum-blue photometric method. List of Analysts

1. R. K. Bell, B. B. Bendigo, T. C. Rains, T. A. Rush,

E. R. Deardorff, J. R. Baldwin, R. A. Paulson, W. P. Schmidt, and S. D. Rasberry, Analytical Chemistry Division, Institute for Materials Research, National Bureau of Standards.

2. L. C. Peck, United States Geological Survey, Denver, Colorado.

3. L. M. Melnick, J. D. Selvaggio, and D. G. Cunningham, Applied Research Laboratory, United

States Steel Corporation, Pittsburgh, Pennsylvania. The material for the preparation of this standard was provided by the A. P. Green Fire Brick Company,

Mexico, Missouri. The overall direction and coordination of the technical measurements leading to certification were performed under the chairmenship of O. Menis and J. I. Shultz. The technical and support aspects involved in the preparation, certification and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials by J. L. Hague.

lington, D. C. 20234 J. Paul Cali, Acting Chief October 8, 1969 Office of Standard Reference Materials

77

jFORM NBS-114A (1-71) u.s. dept. of comm. 1 . PU BLIC ATION OR RE PORT NO. 2. Gov't Access BIBLIOGRAPHIC DATA NBSSP 260-37 N°-

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

StZ3.rid3.lTcl L G TGHC6 M3 t S Jf 2.3 L S

° Methods of Analysis of NBS Clay Standards

5. Publication Date June 1972

6. Performing Organization Code

7. AUTHOR(S) J. I. Shultz, R. K. Bell. T. C. Rains and 0. Menis

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Address Same as 9

.

13. Type of Report & Period ; Coveredfinal

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) This publication brings together a compilation of methods

used at NBS for the analysis of two complex standard ref- erence clay materials. The methods were selected to give

the best obtainable results for those elements normally

found in clays. In some instances, more than one procedure

was employed for an element as a cross-check on the precision and accuracy of the results. The procedures are presented in two parts . Part I is concerned with the determination of the major constituents by the classical

analytical procedures. Part II covers the minor elements

which are determined instrumentally by flame emission and atomic absorption spectrometry. These clay materials

serve as analytical composition standards to provide quality

control of the basic raw materials which are used in the ceramics and refractories industries.

17. KEY WORDS (Alphabetical order, separated by semicolons) Atomic absorption;

classical procedures; clay materials; flame emission;

Standard Reference Materials

.

ceramics;

refractories

;

18. AVAILABILITY STATEMENT

P^T UNLIMITED. FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

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