3113 METALS BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY*

3113 A. Introduction

1. Applications

Electrothermal atomic absorption permits determination of

most metallic elements with sensitivities and detection limits

from 20 to 1000 times better than those of conventional flame

techniques without extraction or sample concentration. This

increase in sensitivity results from an increase in atom density

within the furnace as compared to flame atomic absorption.

Many elements can be determined at concentrations as low as

1.0 g/L. An additional advantage of electrothermal atomic

absorption is that only a very small volume of sample is

required.

The electrothermal technique is used only at concentration

levels below the optimum range of direct flame atomic absorption because it is subject to more interferences than the flame

procedure and requires increased analysis time. The method of

standard additions may be required to insure validity of data.

Because of the high sensitivity of this technique, it is extremely

susceptible to contamination; extra care in sample handling and

analysis may be required.

2. Principle

Electrothermal atomic absorption spectroscopy is based on the

same principle as direct flame atomization but an electrically

heated atomizer or graphite furnace replaces the standard burner

head. A discrete sample volume is dispensed into the graphite

sample tube (or cup). Typically, determinations are made by

heating the sample in three or more stages. First, a low current

heats the tube to dry the sample. The second, or charring, stage

destroys organic matter and volatilizes other matrix components

at an intermediate temperature. Finally, a high current heats the

tube to incandescence and, in an inert atmosphere, atomizes the

element being determined. Additional stages frequently are

added to aid in drying and charring, and to clean and cool the

tube between samples. The resultant ground-state atomic vapor

absorbs monochromatic radiation from the source. A photoelectric detector measures the intensity of transmitted radiation. The

inverse of the transmittance is related logarithmically to the

absorbance, which is directly proportional to the number density

of vaporized ground-state atoms (the Beer-Lambert law) over a

limited concentration range.

3. Interferences

Electrothermal atomization determinations may be subject to

significant interferences from molecular absorption as well as

chemical and matrix effects. Molecular absorption may occur

when components of the sample matrix volatilize during atomization, resulting in broadband absorption. Several background

correction techniques are available commercially to compensate

for this interference. A continuum source such as a deuterium arc

can correct for background up to absorbance levels of about 0.8.

Continuum lamp intensity diminishes at long wavelengths and

use of continuum background correction is limited to analytical

wavelengths below 350 nm. Zeeman effect background correctors can handle background absorbance up to 1.5 to 2.0. The

Smith-Hieftje correction technique can accommodate background absorbance levels as large as 2.5 to 3.0 (see Section

3111A.3). Both Zeeman and Smith-Hieftje background corrections are susceptible to rollover (development of a negative

absorbance-concentration relationship) at high absorbances. The

rollover absorbance for each element should be available in the

manufacturer’s literature. Curvature due to rollover should become apparent during calibration; dilution produces a more

linear calibration plot. Use background correction when analyzing samples containing high concentrations of acid or dissolved

solids and in determining elements for which an absorption line

below 350 nm is used.

Matrix modification can be useful in minimizing interference

and increasing analytical sensitivity. Determine need for a modifier by evaluating recovery of a sample with a known addition.

Recovery near 100% indicates that sample matrix does not affect

analysis. Chemical modifiers generally modify relative volatilities of matrix and metal. Some modifiers enhance matrix removal, isolating the metal, while other modifiers inhibit metal

volatilization, allowing use of higher ashing/charring temperatures and increasing efficiency of matrix removal. Chemical

modifiers are added at high concentration (percent level) and can

lead to sample contamination from impurities in the modifier

solution. Heavy use of chemical modifiers may reduce the useful

life (normally 50 to 100 firings) of the graphite tube. Some

specific chemical modifiers and approximate concentrations are

listed in Table 3113:I.

Addition of a chemical modifier directly to the sample before

analysis is restricted to inexpensive additives (e.g. phosphoric

acid). Use of palladium salts for matrix modification normally

requires methods of co-addition, in which sample and modifier

are added consecutively to the furnace either manually or, preferably, with an automatic sampler. Palladium salts (nitrate is

preferred, chloride is acceptable) are listed in Table 3113:I as a

modifier for many metals. The palladium solution (50 to 2000

mg/L) generally includes citric or ascorbic acid, which aids

reduction of palladium in the furnace. Citric acid levels of 1 to

2% are typical. Use of hydrogen (5%) in the coolant gas (available commercially as a mixture) also reduces palladium, eliminating need for organic reducing acids. CAUTION: Do not mix

hydrogen and other gases in the laboratory; hydrogen gas is

very flammable—handle with caution. Use low levels of palladium (50 to 250 mg/L) for normal samples and higher levels for

complex samples. Addition of excess palladium modifier may

widen atomization peaks; in such cases peak area measurements * Approved by Standard Methods Committee, 1999.

Joint Task Group: 20th Edition—Raymond J. Lovett (chair), David J. Kaptain.

ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY (3113)/Introduction 3-25
may provide higher quality results. The recommended mode of

modifier use is through co-addition to the furnace of about 10 L

of the palladium (or other) modifier solution. Palladium may not

be the best modifier in all cases and cannot be recommended

unconditionally. Test samples requiring a modifier first with

palladium; test other modifiers only if palladium is unsuccessful

or to minimize modifier cost. See Section 3113B.3 for preparation of modifier solution.

Temperature ramping, i.e., gradual heating, can be used to

decrease background interferences and permits analysis of samples with complex matrices. Ramping permits a controlled, continuous increase of furnace temperature in any of the various

steps of the temperature sequence. Ramp drying is used for

samples containing mixtures of solvents or for samples with a

high salt content (to avoid spattering). If spattering is suspected,

develop drying ramp by visual inspection of the drying stage,

using a mirror. Samples that contain a complex mixture of matrix

components sometimes require ramp charring to effect controlled, complete thermal decomposition. Ramp atomization may

minimize background absorption by permitting volatilization of

the element being determined before the matrix. This is especially applicable in the determination of such volatile elements

as cadmium and lead. Use of time-resolved absorbance profiles

(available on most modern instruments) greatly aids method

development. Changes in atomization, notably the element peak

appearance time and magnitude of background and metal absorbances, can be monitored directly.

Improve analysis by using a graphite platform, inserted into

the graphite tube, as the atomization site. The platform is not

heated as directly by the current flowing through the graphite

tube; thus the metal atomizes later and under more uniform

conditions.

Use standard additions to compensate for matrix interferences.

When making standard additions, determine whether the added

metal and that in the sample behave similarly under the specified

conditions. [See Section 3113B.4d2)]. In the extreme, test every

sample for recovery (85 to 115% recovery desired) to determine

if standard addition is needed. Test every new sample type for

recovery. Recovery of only 40 to 85% generally indicates that

standard addition is required. Often, as long as the samples are

from sources of consistent properties, a representative recovery

can be used to characterize the analysis and determine the

necessity of standard addition. Test samples of unknown origin

or of complex composition (digestates, for example) individually

for metal recovery. Ideally, chemical modifiers and graphite

platforms render the sample fit to be analyzed using a standard

analytical calibration curve. Always verify this assumption;

however, a properly developed method with judicious use of

chemical modifiers should eliminate the necessity for standard

addition in all but the most extreme samples.

Chemical interaction of the graphite tube with various elements to form refractory carbides occurs at high charring and

atomization temperatures. Elements that form carbides are barium, molybdenum, nickel, titanium, vanadium, and silicon. Carbide formation is characterized by broad, tailing atomization

peaks and reduced sensitivity. Using pyrolytically coated tubes

for these metals minimizes the problem.

4. Sensitivity, Detection Levels, and Optimum

Concentration Range

Estimated detection levels and optimum concentration ranges

are listed in Table 3113:II. These values may vary with the

chemical form of the element being determined, sample composition, or instrumental conditions.

For a given sample, increased sensitivity may be achieved by

using a larger sample volume or by reducing flow rate of the

purge gas or by using gas interrupt during atomization. Note,

however, that these techniques also will increase the effects of

any interferences present. Sensitivity can be decreased by diluting the sample, reducing sample volume, increasing purge-gas

flow, or using a less sensitive wavelength. Use of argon, rather

than nitrogen, as the purge gas generally improves sensitivity

and reproducibility. Hydrogen mixed with the inert gas may

suppress chemical interference and increase sensitivity by acting

TABLE 3113:I. POTENTIAL MATRIX MODIFIERS FOR ELECTROTHERMAL

ATOMIC ABSORPTION SPECTROMETRY*

Modifier

Analyses for Which

Modifier

May Be Useful

1500 mg Pd/L 1000 mg

Mg(NO3)2/L1

Ag, As, Au, Bi, Cu, Ge, Mn,

Hg, In, Sb, Se, Sn, Te, Tl

500–2000 mg Pd/L reducing

agent2

†

Ag, As, Bi, Cd, Co, Cr, Cu, Fe,

Hg, Mn, Ni, Pb, Sb

5000 mg Mg(NO3)2/L1 Be, Co, Cr, Fe, Mn, V

100–500 mg Pd/L2 As, Ga, Ge, Sn

50 mg Ni/L2 As, Se, Sb

2% PO4

3	 1000 mg Mg (NO3)2/L1 Cd, Pb

*Assumes 10 L modifier/10 L sample.

†Citric acid (1–2%) preferred; ascorbic acid or H2 acceptable.

TABLE 3113:II. DETECTION LEVELS AND CONCENTRATION RANGES FOR

ELECTROTHERMAL ATOMIZATION ATOMIC ABSORPTION SPECTROMETRY

Element

Wavelength

nm

Estimated

Detection

Level

g/L

Optimum

Concentration

Range

g/L

Al 309.3 3 20–200

Sb 217.6 3 20–300

As 193.7 1 5–100

Ba 553.6 2 10–200

Be 234.9 0.2 1–30

Cd 228.8 0.1 0.5–10

Cr 357.9 2 5–100

Co 240.7 1 5–100

Cu 324.7 1 5–100

Fe 248.3 1 5–100

Pb* 283.3 1 5–100

Mn 279.5 0.2 1–30

Mo 313.3 1 3–60

Ni 232.0 1 5–100

Se 196.0 2 5–100

Ag 328.1 0.2 1–25

Sn 224.6 5 20–300

*The more sensitive 217.0-nm wavelength is recommended for instruments with

background correction capabilities.

3-26 METALS (3000)
as a reducing agent, thereby aiding in producing more groundstate atoms. Pyrolytically coated graphite tubes can increase

sensitivity for the more refractory elements and are recommended. The optical pyrometer/maximum power accessory

available on some instruments also offers increased sensitivity

with lower atomization temperatures for many elements.

Using the Stabilized Temperature Platform Furnace (STPF)

technique, which is a combination of individual techniques, also

offers significant interference reduction with improved sensitivity. Sensitivity changes with sample tube age. Discard graphite

tubes when significant variations in sensitivity or poor reproducibility are observed. The use of high acid concentrations, brine

samples, and matrix modifiers often drastically reduces tube life.

Preferably use the graphite platform in such situations.

5. References

1. PERKIN-ELMER CORP. 1991. Summary of Standard Conditions for

Graphite Furnace. Perkin-Elmer Corp., Norwalk, Conn.

2. ROTHERY, E., ed. 1988. Analytical Methods for Graphite Tube Atomizers. Varian Techtron Pty, Ltd., Mulgrave, Victoria, Australia.

6. Bibliography

FERNANDEZ, F.J. & D.C. MANNING. 1971. Atomic absorption analyses of

metal pollutants in water using a heated graphite atomizer. Atomic

Absorption Newsletter 10:65.

SEGAR, D.A. & J.G. GONZALEZ. 1972. Evaluation of atomic absorption

with a heated graphite atomizer for the direct determination of trace

transition metals in sea water. Anal. Chim. Acta 58:7.

BARNARD, W.M. & M.J. FISHMAN. 1973. Evaluation of the use of heated

graphite atomizer for the routine determination of trace metals in

water. Atomic Absorption Newsletter 12:118.

KAHN, H.L. 1973. The detection of metallic elements in wastes and

waters with the graphite furnace. Int. J. Environ. Anal. Chem.

3:121.

WALSH, P.R., J.L. FASCHING & R.A. DUCE. 1976. Matrix effects and their

control during the flameless atomic absorption determination of

arsenic. Anal. Chem. 48:1014.

HENN, E.L. 1977. Use of Molybdenum in Eliminating Matrix Interferences in Flameless Atomic Absorption. Spec. Tech. Publ. 618,

American Soc. Testing & Materials, Philadelphia, Pa.

MARTIN, T.D. & J.F. KOPP. 1978. Methods for Metals in Drinking Water.

U.S. Environmental Protection Agency, Environmental Monitoring

and Support Lab., Cincinnati, Ohio.

HYDES, D.J. 1980. Reduction of matrix effects with a soluble organic

acid in the carbon furnace atomic absorption spectrometric determination of cobalt, copper, and manganese in seawater. Anal.

Chem. 52:289.

SOTERA, J.J. & H.L. KAHN. 1982. Background correction in AAS. Amer.

Lab. 14:100.

SMITH, S.B. & G.M. HIEFTJE. 1983. A new background-correction

method for atomic absorption spectrometry. Appl. Spectrosc. 37:

419.

GROSSER, Z. 1985. Techniques in Graphite Furnace Atomic Absorption

Spectrophotometry. Perkin-Elmer Corp., Ridgefield, Conn.

SLAVIN, W. & G.R. CARNICK. 1985. A survey of applications of the

stabilized temperature platform furnace and Zeeman correction.

Atomic Spectrosc. 6:157.

BRUEGGEMEYER, T. & F. FRICKE. 1986. Comparison of furnace & atomization behavior of aluminum from standard & thorium-treated

L’vov platforms. Anal. Chem. 58:1143.

3113 B. Electrothermal Atomic Absorption Spectrometric Method

1. General Discussion

This method is suitable for determination of micro quantities

of aluminum, antimony, arsenic, barium, beryllium, cadmium,

chromium, cobalt, copper, iron, lead, manganese, molybdenum,

nickel, selenium, silver, and tin. It is also applicable to analysis

of bismuth, gallium, germanium, gold, indium, mercury, tellurium, thallium, and vanadium, but precision and accuracy data

are not yet available.

2. Apparatus

a. Atomic absorption spectrometer: See Section 3111A.6a.

The instrument must have background correction capability.

b. Source lamps: See Section 3111A.6d.

c. Graphite furnace: Use an electrically heated device with

electronic control circuitry designed to carry a graphite tube or

cup through a heating program that provides sufficient thermal

energy to atomize the elements of interest. Furnace heat controllers with only three heating steps are adequate only for fresh

waters with low dissolved solids content. For salt waters, brines,

and other complex matrices, use a furnace controller with up to

seven individually programmed heating steps. Fit the furnace

into the sample compartment of the spectrometer in place of the

conventional burner assembly. Use argon as a purge gas to

minimize oxidation of the furnace tube and to prevent the formation of metallic oxides. Use graphite tubes with platforms to

minimize interferences and to improve sensitivity.

d. Readout: See Section 3111A.6c.

e. Sample dispensers: Use microliter pipets (5 to 100 L) or

an automatic sampling device designed for the specific instrument.

f. Vent: See Section 3111A.6f.

g. Cooling water supply: Cool with tap water flowing at 1 to

4 L/min or use a recirculating cooling device.

h. Membrane filter apparatus: Use an all-glass filtering device

and 0.45-m or smaller-pore-diameter membrane filters. For

trace analysis of aluminum, use polypropylene or TFE devices.

3. Reagents

a. Metal-free water: See Section 3111B.3c.

b. Hydrochloric acid, HCl, 1 1 and conc.

c. Nitric acid, HNO3, 1 1 and conc.

d. Matrix modifier stock solutions:

1) Magnesium nitrate, 10 000 mg Mg/L: Dissolve 10.5 g

Mg(NO3)2 6H2O in water. Dilute to 100 mL.

ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY (3113)/Electrothermal Atomic Absorption Spectrometric Method 3-27
2) Nickel nitrate, 10 000 mg Ni/L: Dissolve 4.96 g

Ni(NO3)2 6H2O in water. Dilute to 100 mL.

3) Phosphoric acid, 10% (v/v): Add 10 mL conc H3PO4 to

water. Dilute to 100 mL.

4) Palladium nitrate, 4000 mg Pd/L: Dissolve 8.89 g

Pd(NO3)2 H2O in water. Dilute to 1 L.

5) Citric acid, 4%: Dissolve 40 g citric acid in water. Dilute to

1 L.

NOTE: All of the modifier solutions recommended in Table

3113:I can be prepared with volumetric combination of the

above solutions and water. For preparation of other matrix modifiers, see references or follow manufacturers’ instructions.

e. Stock metal solutions: Refer to Sections 3111B and 3114.

f. Chelating resin: 100 to 200 mesh* purified by heating at

60°C in 10N NaOH for 24 h. Cool resin and rinse 10 times each

with alternating portions of 1N HCl, metal-free water, 1N NaOH,

and metal-free water.

g. Metal-free seawater (or brine): Fill a 1.4-cm-ID  20-cmlong borosilicate glass column to within 2 cm of the top with

purified chelating resin. Elute resin with successive 50-mL portions of 1N HCl, metal-free water, 1N NaOH, and metal-free

water at the rate of 5 mL/min just before use. Pass salt water or

brine through the column at a rate of 5 mL/min to extract trace

metals present. Discard the first 10 bed volumes (300 mL) of

eluate.

4. Procedures

a. Sample pretreatment: Before analysis, pretreat all samples

as indicated below. Rinse all glassware with 1 1 HNO3 and

water. Carry out digestion procedures in a clean, dust-free laboratory area to avoid sample contamination. For digestion of trace

aluminum, use polypropylene or TFE utensils to avoid leachable

aluminum from glassware.

1) Dissolved metals—See Section 3030B. For samples requiring arsenic and/or selenium analysis add 3 mL 30% hydrogen

peroxide/100 mL sample and an appropriate volume of nickel

nitrate solution (see Table 3113:I) before analysis. For all other

metals no further pretreatment is required except for adding an

optional matrix modifier.

2) Total recoverable metals (Al, Sb, Ba, Be, Cd, Cr, Co, Cu,

Fe, Pb, Mn, Mo, Ni, Ag, and Sn)—NOTE: Sb and Sn are not

recovered unless HCl is used in the digestion. See Section

3030D. Quantitatively transfer digested sample to a 100-mL

volumetric flask, add an appropriate amount of matrix modifier

(see Table 3113:I), and dilute to volume with water.

3) Total recoverable metals (As, Se)—Transfer 100 mL of

shaken sample, 1 mL conc HNO3, and 2 mL 30% H2O2 to a

clean, acid-washed 250-mL beaker. Heat on a hot plate without

allowing solution to boil until volume has been reduced to about

50 mL. Remove from hot plate and let cool to room temperature.

Add an appropriate concentration of nickel (see Table 3113:I),

and dilute to volume in a 100-mL volumetric flask with water.

Substitution of palladium is uneconomical. Nickel may be deleted if palladium is co-added during analysis. Simultaneously

prepare a digested blank by substituting water for sample and

proceed with digestion as described above.

b. Instrument operation: Mount and align furnace device

according to manufacturer’s instructions. Turn on instrument and

data collection system. Select appropriate light source and adjust

to recommended electrical setting. Select proper wavelength and

set all conditions according to manufacturer’s instructions, including background correction. Background correction is important when elements are determined at short wavelengths or when

sample has a high level of dissolved solids. Background correction normally is not necessary at wavelengths longer than 350

nm. If background correction above 350 nm is needed deuterium

arc background correction is not useful and other types must be

used.

Select proper inert- or sheath-gas flow. In some cases, it is

desirable to interrupt the inert-gas flow during atomization. Such

interruption results in increased sensitivity by increasing residence time of the atomic vapor in the optical path. Gas interruption also increases background absorption and intensifies

interference effects, but modern background correction methods

usually eliminate these problems. Consider advantages and disadvantages of this option for each matrix when optimizing

analytical conditions.

To optimize graphite furnace conditions, carefully adjust furnace

temperature settings to maximize sensitivity and precision and to

minimize interferences. Follow manufacturer’s instructions.

Use drying temperatures slightly above the solvent boiling

point and provide enough time and temperature for complete

evaporation without boiling or spattering.

Select atomization temperature by determining the lowest

temperature providing maximum sensitivity without significantly eroding precision. Optimize by a series of successive

determinations at various atomization temperatures using a standard solution giving an absorbance of 0.2 to 0.5.

The charring temperature must be high enough to maximize

volatilization of interfering matrix components yet too low to

volatilize the element of interest. With the drying and atomization temperatures set to their optimum values, analyze a standard

solution at a series of charring temperatures in increasing increments of 50 to 100°C. When the optimum charring temperature

is exceeded, there will be a significant drop in sensitivity. Plot

charring temperature versus sample absorbance: the optimum

charring temperature is the highest temperature without reduced

sensitivity. Verify optimization with major changes in sample

matrix.

c. Instrument calibration: Prepare standard solutions for instrument calibration by diluting metal stock solutions. Prepare

standard solutions fresh daily.

Prepare a blank and at least three calibration standards in the

appropriate concentration range (see Table 3113:II) for correlating element concentration and instrument response. Match the

matrix of the standard solutions to those of the samples as

closely as possible. In most cases, this simply requires matching

the acid background of the samples. For seawaters or brines,

however, use the metal-free matrix (¶ 3g) as the standard solution diluent. In addition, add the same concentration of matrix

modifier (if required for sample analysis) to the standard solutions.

Inject a suitable portion of each standard solution, in order of

increasing concentration. Analyze each standard solution in triplicate to verify method precision. * Chelex 100, or equivalent, available from Bio-Rad Laboratories, Richmond,

CA.

3-28 METALS (3000)
Construct an analytical curve by plotting the average peak

absorbances or peak areas of the standard solution versus concentration on linear graph paper. Alternatively, use electronic

instrument calibration if the instrument has this capability.

d. Sample analysis: Analyze all samples except those demonstrated to be free of matrix interferences (based on recoveries of

85% to 115% for known additions) using the method of standard

additions. Analyze all samples at least in duplicate or until

reproducible results are obtained. A variation of  10% is

considered acceptable reproducibility. Average replicate values.

1) Direct determination—Inject a measured portion of pretreated sample into the graphite furnace. Use the same volume as

was used to prepare the calibration curve. Usually add modifier

immediately after the sample, preferably using an automatic

sampler or a micropipet. Some methods require modifier to be

injected before the sample. Use the same volume and concenTABLE 3113:III. INTERLABORATORY SINGLE-ANALYST PRECISION DATA FOR ELECTROTHERMAL ATOMIZATION METHODS1

Single-Analyst Precision

% RSD

Element

Concentration

g/L

Lab

Pure

Water

Drinking

Water

Surface

Water

Effluent

1

Effluent

2

Effluent

3

Al 28 66 108 70 — — 66

125 27 35 24 — — 34

11 000 11 — — 22 — —

58 300 27 — — 19 — —

460 9 — —— 30 —

2 180 28 — —— 4 —

10.5 20 13 13 13 56 18

230 10 18 13 21 94 14

As 9.78 40 25 15 74 23 11

227 10 6 8 11 15 6

Ba 56.5 36 21 29 59 23 27

418 14 12 20 24 24 18

Be 0.45 18 27 15 30 2 11

10.9 14 4 9 7 12 12

Cd 0.43 72 49 1 121 35 27

12 11 17 22 14 11 15

Cr 9.87 24 33 10 23 15 10

236 16 7 11 13 16 7

Co 29.7 10 17 10 19 24 12

420 8 11 13 14 9 5

Cu 10.1 49 47 17 17 — 30

234 8 15 6 21 — 11

300 6 — —— 11 —

1 670 11 — —— 6 —

Fe 26.1 144 52 153 — — 124

455 48 37 45 — — 31

1 030 17 — — 30 — —

5 590 6 — — 32 — —

370 14 — —— 19 —

2 610 9 — —— 18 —

Pb 10.4 6 19 17 21 19 33

243 17 7 17 18 12 16

Mn 0.44 187 180 — —— 275

14.8 32 19 — —— 18

91.0 15 — — 48 — —

484.0 4 — — 12 — —

111.0 12 — —— 21 —

666.0 6 — —— 20 —

Ni 26.2 20 26 25 24 18 9

461.0 15 11 9 8 11 4

Se 10.0 12 27 16 35 41 13

235.0 6 6 15 6 13 14

Ag 8.48 10 — — 15 27 16

56.5 14 — — 7 16 23

0.45 27 166 48 —— —

13.6 15 4 10 —— —

ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY (3113)/Electrothermal Atomic Absorption Spectrometric Method 3-29
tration of modifier for all standards and samples. Dry, char, and

atomize according to the preset program. Repeat until reproducible results are obtained.

Compare the average absorbance value or peak area to the

calibration curve to determine concentration of the element of

interest. Alternatively, read results directly if the instrument is

equipped with this capability. If absorbance (or concentration) or

peak area of the sample is greater than absorbance (concentration) or peak area of the most concentrated standard solution,

dilute sample and reanalyze. If very large dilutions are required, another technique (e.g., flame AA or ICP) may be

more suitable for this sample. Large dilution factors magnify

small errors on final calculation. Keep acid background and

concentration of matrix modifier (if present in the solutions)

constant. Dilute the sample in a blank solution of acid and

matrix modifiers.

TABLE 3113:IV. INTERLABORATORY OVERALL PRECISION DATA FOR ELECTROTHERMAL ATOMIZATION METHODS1

Overall Precision

% RSD

Element

Concentration

g/L

Lab

Pure

Water

Drinking

Water

Surface

Water

Effluent

1

Effluent

2

Effluent

3

Al 28 99 114 124 — — 131

125 45 47 49 — — 40

11 000 19 — — 43 — —

58 300 31 — — 32 — —

460 20 — —— 47 —

2 180 30 — —— 15 —

10.5 37 19 22 50 103 39

230 26 16 16 17 180 21

As 9.78 43 26 37 72 50 39

227 18 12 13 20 15 14

Ba 56.5 68 38 43 116 43 65

418 35 35 28 38 48 16

Be 0.45 28 31 15 67 50 35

10.9 33 15 26 20 9 19

Cd 0.43 73 60 5 88 43 65

12 19 25 41 26 20 27

Cr 9.87 30 53 24 60 41 23

236 18 14 24 20 14 20

Co 29.7 13 26 17 18 21 17

420 21 21 17 18 13 13

Cu 10.1 58 82 31 32 — 74

234 12 33 19 21 — 26

300 13 — —— 14 —

1 670 12 — —— 13 —

Fe 26.1 115 93 306 — — 204

455 53 46 53 — — 44

1 030 32 — — 25 — —

5 590 10 — — 43 — —

370 28 — —— 22 —

2 610 13 — —— 22 —

Pb 10.4 27 42 31 23 28 47

243 18 19 17 19 19 25

Mn 0.44 299 272 ——— 248

14.8 52 41 ——— 29

91.0 16 — — 45 — —

484.0 5 — — 17 — —

111.0 15 — —— 17 —

666.0 8 — —— 24 —

Ni 26.2 35 30 49 35 37 43

461.0 23 22 15 12 21 17

Se 10.0 17 48 32 30 44 51

235.0 16 18 18 17 22 34

Ag 8.48 23 — — 16 35 34

56.5 15 — — 24 32 28

0.45 57 90 368 ———

13.6 19 19 59 ———

3-30 METALS (3000)
Proceed to ¶ 5a below.

2) Method of standard additions—Refer to ¶ 4c above. The

method of standard additions is valid only when it falls in the

linear portion of the calibration curve. Once instrument sensitivity has been optimized for the element of interest and the linear

range for the element has been established, proceed with sample

analyses.

Inject a measured volume of sample into furnace device. Dry,

char or ash, and atomize samples according to preset program.

Repeat until reproducible results are obtained. Record instrument

response in absorbance or concentration as appropriate. Add a

known concentration of the element of interest to a separate portion

of sample so as not to change significantly the sample volume.

Repeat the determination.

TABLE 3113:V. INTERLABORATORY RELATIVE ERROR DATA FOR ELECTROTHERMAL ATOMIZATION METHODS1

Relative Error

%

Element

Concentration

g/L

Lab

Pure

Water

Drinking

Water

Surface

Water

Effluent

1

Effluent

2

Effluent

3

Al 28.0 86 150 54 — — 126

125.0 4 41 39 — — 30

11 000.0 2 — — 14 — —

58 300.0 12 — — 7 — —

460.0 2 — —— 11 —

2 180.0 11 — —— 9 —

Sb 10.5 30 32 28 24 28 36

230.0 35 14 19 13 73 39

As 9.78 36 1 22 106 13 16

227.0 3 7 10 19 6 13

Ba 56.5 132 54 44 116 59 40

418.0 4 0 0 13 6 60

Be 0.45 40 16 11 16 10 15

10.9 13 2 9 7 8 8

Cd 0.43 58 45 37 66 16 19

12.0 4 6 5 22 18 3

Cr 9.87 10 9 4 2 5 15

236.0 11 0 9 13 5 8

Co 29.7 7 7 1 6 3 13

420.0 12 8 8 11 5 18

Cu 10.1 16 48 2 5 — 15

234.0 8 7 0 4 — 19

300.0 4 — —— 21 —

1 670.0 6 — —— 2 —

Fe 26.1 85 60 379 — — 158

455.0 43 22 31 — — 18

1 030.0 8 — — 8 — —

5 590.0 2 — — 12 — —

370.0 4 — —— 11 —

2 610.0 35 — —— 2 —

Pb 10.4 16 10 17 1 34 14

243.0 5 15 8 18 15 29

Mn 0.44 332 304 — —— 556

14.8 10 1 — —— 36

91.0 31 — — 10 — —

484.0 42 — — 4 — —

111.0 1 — —— 29 —

666.0 6 — —— 23 —

Ni 26.2 9 16 10 7 33 54

461.0 15 19 18 31 16 18

Se 10.0 12 9 6 36 17 37

235.0 7 7 0 13 10 17

Ag 8.48 12 — — 1 51 20

56.5 16 — — 8 51 22

0.45 34 162 534 —— —

13.6 3 12 5 —— —

ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY (3113)/Electrothermal Atomic Absorption Spectrometric Method 3-31
Add a known concentration (preferably twice that used in the

first addition) to a separate sample portion. Mix well and repeat

the determination.

Using linear graph paper, plot average absorbance or instrument response for the sample and the additions on the vertical

axis against the concentrations of the added element on the

horizontal axis, using zero as the concentration for the sample.

Draw a straight line connecting the three points and extrapolate

to zero absorbance. The intercept at the horizontal axis is the

negative of the element concentration in the sample. The concentration axis to the left of the origin should be a mirror image

of the axis to the right.

5. Calculations

a. Direct determination:

g metal/L  C  F

where:

C  metal concentration as read directly from the instrument or

from the calibration curve, g/L, and

F  dilution factor.

b. Method of additions:

g metal/L  C  F

where:

C  metal concentration as read from the method of additions

plot, g/L, and

F  dilution factor.

6. Precision and Bias

Data typical of the precision and bias obtainable are presented

in Tables 3113:III, IV, and V.

7. Quality Control

See Section 3020 for specific quality control procedures to

be followed during analysis. Although previous indications

were that very low optimum concentration ranges were attainable for most metals (see Table 3113:II), data in Table

3113:III using variations of these protocols show that this

may not be so. Exercise extreme care when applying this

method to the lower concentration ranges. Verify analyst

precision at the beginning of each analytical run by making

triplicate analyses. Verify autosampler precision by checking

volumes (by weight) delivered by the autosampler at routinely

used injection volume settings.

8. Reference

1. COPELAND, T.R. & J.P. MANEY. 1986. EPA Method Study 31: Trace

Metals by Atomic Absorption (Furnace Techniques). EPA-600/S4-

85-070, U.S. Environmental Protection Agency, Environmental

Monitoring and Support Lab., Cincinnati, Ohio.

9. Bibliography

RENSHAW, G.D. 1973. The determination of barium by flameless atomic

absorption spectrophotometry using a modified graphite tube atomizer. Atomic Absorption Newsletter 12:158.

YANAGISAWA, M., T. TAKEUCHI & M. SUZUKI. 1973. Flameless atomic

absorption spectrometry of antimony. Anal. Chim. Acta 64:381.

RATTONETTI, A. 1974. Determination of soluble cadmium, lead, silver

and indium in rainwater and stream water with the use of flameless

atomic absorption. Anal. Chem. 46:739.

HENN, E.L. 1975. Determination of selenium in water and industrial

effluents by flameless atomic absorption. Anal. Chem. 47:428.

MARTIN, T.D. & J.F. KOPP. 1975. Determining selenium in water, wastewater, sediment and sludge by flameless atomic absorption spectrometry. Atomic Absorption Newsletter 14:109.

MARUTA, T., K. MINEGISHI & G. SUDOH. 1976. The flameless atomic

absorption spectrometric determination of aluminum with a carbon

atomization system. Anal. Chim. Acta 81:313.

CRANSTON, R.E. & J.W. MURRAY. 1978. The determination of chromium

species in natural waters. Anal. Chim. Acta 99:275.

HOFFMEISTER, W. 1978. Determination of iron in ultrapure water by

atomic absorption spectroscopy. Z. Anal. Chem. 50:289.

LAGAS, P. 1978. Determination of beryllium, barium, vanadium and

some other elements in water by atomic absorption spectrometry

with electrothermal atomization. Anal. Chim. Acta 98:261.

CARRONDO, M.J.T., J.N. LESTER & R. PERRY. 1979. Electrothermal

atomic absorption determination of total aluminum in waters and

waste waters. Anal. Chim. Acta 111:291.

NAKAHARA, T. & C.L. CHAKRABARTI. 1979. Direct determination of traces

of molybdenum in synthetic sea water by atomic absorption spectrometry with electrothermal atomization and selective volatilization of the salt matrix. Anal. Chim. Acta 104:99.

TIMINAGA, M. & Y. UMEZAKI. 1979. Determination of submicrogram

amounts of tin by atomic absorption spectrometry with electrothermal atomization. Anal. Chim. Acta 110:55.

3-32 METALS (3000)