200.12 - 1

Method 200.12

Determination of Trace Elements in Marine Waters by Stabilized

Temperature Graphite Furnace Atomic Absorption

John T. Creed and Theodore D. Martin

Chemical Exposure Research Branch

Human Exposure Research Division

Revision 1.0

September 1997

National Exposure Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, Ohio 45268
Revision 1.0 September 1997 200.12 - 2

Chemical Abstracts

Service Registry

Analyte Numbers (CASRN)

Arsenic (As) 7440-38-2

Cadmium (Cd) 7440-43-9

Chromium (Cr) 7440-47-3

Copper (Cu) 7440-50-8

Lead (Pb) 7439-92-1

Nickel (Ni) 7440-02-0

Selenium (Se) 7782-49-2

Method 200.12

Determination of Trace Elements in Marine Waters by Stabilized 

Temperature Graphite Furnace Atomic Absorption

1.0 Scope and Application

1.1 This method provides procedures for the

determination of total recoverable elements by graphite

furnace atomic absorption (GFAA) in marine waters,

including estuarine, ocean and brines with salinities of up

to 35 ppt. This method is applicable to the following

analytes: 

1.2 For determination of total recoverable analytes in

marine waters, a digestion/extraction is required prior to

analysis.

1.3 Method detection limit and instrumental operating

conditions for the applicable elements are listed in Tables

1 and 2. These are intended as a guide and are typical of

a commercial instrument optimized for the element.

However, actual method detection limits and linear working ranges will be dependent on the sample matrix,

instrumentation and selected operating conditions.

1.4 Users of the method data should state the data

quality objectives prior to analysis. The ultra-trace metal

concentrations typically associated with marine water may

preclude the use of this method based on its sensitivity.

Users of the method must document and have on file the

required initial demonstration performance data described

in Section 9.2 prior to using the method for analysis.

2.0 Summary of Method

2.1 Nitric acid is dispensed into a beaker containing

an accurately weighed or measured, well-mixed, 

homogeneous aqueous sample. Then, for samples with

undissolved material, the beaker is covered with a watch

glass and heated, made up to volume, centrifuged or

allowed to settle, and the sample is then analyzed.

2.2 The analytes listed in this method are determined

by stabilized temperature platform graphite furnace

atomic absorption (STPGFAA). In STPGFAA, the sample

and the matrix modifier are first pipetted onto the platform

or a device which provides delayed atomization. 

The furnace chamber is then purged with a continuous

flow of a premixed gas (95% argon - 5% hydrogen) and

the sample is dried at a relatively low temperature (about

120EC) to avoid spattering. Once dried, the sample is

pretreated in a char or ashing step which is designed to

minimize the interference effects caused by the concomitant sample matrix. After the char step, the furnace is

allowed to cool prior to atomization. The atomization

cycle is characterized by rapid heating of the furnace to a

temperature where the metal (analyte) is atomized from

the pyrolytic graphite surface into a stopped gas flow

atmosphere of argon containing 5% hydrogen. (Only

selenium is determined in an atmosphere of high purity

argon.) The resulting atomic cloud absorbs the elementspecific atomic emission produced by a hollow cathode

lamp (HCL) or an electrodeless discharge lamp (EDL).

Following analysis, the furnace is subjected to a cleanout

period of high temperature and continuous argon flow.

Because the resulting absorbance usually has a nonspecific component associated with the actual analyte absorbance, Zeeman background correction is required to

subtract from the total signal the component which is

nonspecific to the analyte. In the absence of interferences, the background-corrected, absorbance is directly

related to the concentration of the analyte. Interferences

relating to STPGFAA (Section 4.0) must be recognized

and corrected. Suppressions or enhancements of instrument response caused by the sample matrix must be

corrected for by the method of standard addition (Section

11.3).
200.12 - 3 Revision 1.0 September 1997

3.0 Definitions

3.1 Calibration Blank (CB) -- A volume of reagent

water fortified with the same matrix as the calibration

standards, but without the analytes, internal standards, or

surrogate analytes.

3.2 Calibration Standard (CAL) -- A solution prepared from the primary dilution standard solution or stock

standard solutions and the internal standards and surrogate analytes. The CAL solutions are used to calibrate the

instrument response with respect to analyte concentration.

3.3 Field Reagent Blank (FRB) -- An aliquot of

reagent water or other blank matrix that is placed in a

sample container in the laboratory and treated as a

sample in all respects, including shipment to the sampling

site, exposure to sampling site conditions, storage,

preservation, and all analytical procedures. The purpose

of the FRB is to determine it method analytes or other

interferences are present in the field environment.

3.4 Instrument Detection Limit (IDL) -- The minimum quantity of analyte or the concentration equivalent

which gives an analyte signal equal to three times the

standard deviation of the background signal at the selected wavelength, mass, retention time, absorbance line,

etc.

3.5 Instrument Performance Check Solution (IPC)

-- A solution of one or more method analytes, surrogates,

internal standards, or other test substances used to

evaluate the performance of the instrument system with

respect to a defined set of criteria.

3.6 Laboratory Duplicates (LD1 and LD2) -- Two

aliquots of the same sample taken in the laboratory and

analyzed separately with identical procedures. Analyses

of LD1 and LD2 indicate precision associated with

laboratory procedures, but not with sample collection,

preservation, or storage procedures.

3.7 Laboratory Fortified Blank (LFB) -- An aliquot

of reagent water or other blank matrices to which known

quantities of the method analytes are added in the

laboratory. The LFB is analyzed exactly like a sample,

and its purpose is to determine whether the methodology

is in control, and whether the laboratory is capable of

making accurate and precise measurements.

3.8 Laboratory Fortified Sample Matrix (LFM) -- An

aliquot of an environmental sample to which known

quantities of the method analytes are added in the

laboratory. The LFM is analyzed exactly like a sample,

and its purpose is to determine whether the sample matrix

contributes bias to the analytical results. The background

concentrations of the analytes in the sample matrix must

be determined in a separate aliquot and the measured

values in the LFM corrected for background concentrations.

3.9 Laboratory Reagent Blank (LRB) -- An aliquot

of reagent water or other blank matrices that are treated

exactly as a sample including exposure to all glassware,

equipment, solvents, reagents, internal standards, and

surrogates that are used with other samples. The LRB is

used to determine if method analytes or other interferences are present in the laboratory environment, the

reagents, or the apparatus.

3.10 Linear Dynamic Range (LDR) -- The absolute

quantity or concentration range over which the instrument

response to an analyte is linear.

3.11 Material Safety Data Sheet (MSDS) -- Written

information provided by vendors concerning a chemical’s

toxicity, health hazards, physical properties, fire, and

reactivity data including storage, spill, and handling precautions.

3.12 Matrix Modifier (MM) -- A substance added to

the instrument along with the sample in order to minimize

the interference effects by selective volatilization of either

analyte or matrix components.

3.13 Matrix Performance Check (MPC) -- A solution

of method analytes used to evaluate the laboratory’s

ongoing capabilities in analyzing high salinity samples.

The reference material NASS-3 or its equivalent is fortified with the same analytes at the same concentration as

the LFB. This provides an ongoing check of furnace

operating conditions to assure the analyte false positives

are not being introduced via elevated backgrounds.

3.14 Method Detection Limit (MDL) -- The minimum

concentration of an analyte that can be identified, measured and reported with 99% confidence that the analyte

concentration is greater than zero.

3.15 Quality Control Sample (QCS) -- A solution of

method analytes of known concentrations which is used

to fortify an aliquot of LRB or sample matrix. The QCS is

obtained from a source external to the laboratory and
Revision 1.0 September 1997 200.12 - 4

different from the source of calibration standards. It is suggested matrix modifiers and the appropriate furnace

used to check laboratory performance with externally charring conditions. Figure 1 is a plot of integrated

prepared test materials. background absorbance vs. char temperature for Ni, Cd,

3.16 Standard Addition -- The addition of a known absorbance in a saline matrix is strongly affected by the

amount of analyte to the sample in order to determine the

relative response of the detector to an analyte within the

sample matrix. The relative response is then used to

assess either an operative matrix effect or the sample

analyte concentration.

3.17 Stock Standard Solution (SSS) -- A concentrated solution containing one or more method analytes

prepared in the laboratory using assayed reference

materials or purchased from a reputable commercial

source.

3.18 Total Recoverable Analyte (TRA) -- The concentration of analyte determined to be in either a solid

sample or an unfiltered aqueous sample following treatment by refluxing with hot dilute mineral acid(s) as

specified in the method.

4.0 Interferences

4.1 Several interference sources may cause

inaccuracies in the determination of trace elements by

GFAA. These interferences can be classified into three

major subdivisions: spectral, matrix, and memory.

4.2 Spectral interferences are caused by absorbance

of light by a molecule or atom which is not the analyte of

interest or emission from black body radiation.

4.2.1 Spectral interferences caused by an element only

occur if there is a spectral overlap between the wavelength of the interfering element and the analyte of

interest. Fortunately, this type of interference is relatively

uncommon in STPGFAA because of the narrow atomic

line widths associated with STPGFAA. In addition, the use

of appropriate furnace temperature programs and high

spectral purity lamps as light sources can minimize the

possibility of this type of interference. However, molecular

absorbances can span several hundred nanometers

producing broadband spectral interferences. This type of

interference is far more common in STPGFAA. The use

of matrix modifiers, selective volatilization, and

background correctors are all attempts to eliminate unwanted nonspecific absorbance. Table 2 contains typical

background absorbances associated with the analysis of

the MPC solution (NASS-3) which has a salinity of 35 ppt.

These background absorbances were obtained using the

Pb, and Se. Figure 1 indicates that the background

char temperature. Therefore, char temperature optimization is a critical part of the successful analysis of metals

in saline water by GFAA. The elevated backgrounds

associated with ocean water can produce false positives.

For this reason, the char temperature profiles shown in

Figure 1 should be constructed for each analyte prior to

using this method for saline water analysis.

Note: False analyte positives can be generated by large

backgrounds. Figure 2 is an atomization profile for Pb

using a 800EC char temperature. The background shown

in the figure has exceeded the capabilities of the Zeeman

corrector. This profile can be used as a guide in screening

other analyses which may have background absorbances

which exceed the Zeeman capability. The background

profile is characterized by a smooth baseline in the

beginning of the atomization cycle followed by a sharp

increase. During this sharp increase the background peak

profile may remain relatively smooth, but when the

background exceeds the Zeeman correction capability,

the background profile will appear extremely erratic. The

atomic profile is also erratic during this part of the atomization cycle. These types of background/atomic profiles

obtained during atomization result in false positives.

Since the nonspecific component of the total absorbance

can vary considerably from sample type to sample type,

to provide effective background correction and eliminate

the elemental spectral interference of palladium on copper and iron on selenium, the exclusive use of Zeeman

background correction is specified in this method.

4.2.2 Spectral interferences are also caused by black

body radiation produced during the atomization furnace

cycle. This black body emission reaches the

photomultiplier tube, producing erroneous results. The

magnitude of this interference can be minimized by

proper furnace tube alignment and monochromator

design. In addition, atomization temperatures which

adequately volatilize the analyte of interest without

producing unnecessary black body radiation can help

reduce unwanted background emission produced during

atomization.

4.3 Matrix interferences are caused by sample components which inhibit the formation of free atomic analyte

atoms during atomization. In this method the use of a

delayed atomization device which provides a warmer gas
200.12 - 5 Revision 1.0 September 1997

phase environment during atomization is required. These response profile is observed in a solution containing

devices provide an environment which is more conducive 10,000 ppm NaCl. Therefore, in well-characterized

to the formation of free analyte atoms and thereby samples of known salinity it is possible to effectively matrix

minimize this type of interference. This type of match the standards with NaCl and perform the analysis

interference can be detected by analyzing the sample directly using matrix matched standards, thereby avoiding

plus a sample aliquot fortified with a known concentration the time consuming method of standard additions. If the

of the analyte. If the determined concentration of the matrix matched standards are going to be used, it is

analyte addition is outside a designated range (Section necessary to document that the use of NaCl is indeed

9.4.3), a possible matrix effect should be suspected. In compensating for the suppression. This documentation

addition, the matrix can produce analyte complexes which should include a response plot of increasing matrix vs.

are lost via volatilization during the char. These losses will relative response similar to Figure 4.

result in poor recovery of the analyte within the matrix and

should be corrected by adjusting the char temperature. 4.5.2 Selenium: The background level associated with

4.4 Memory interferences result from analyzing a

sample containing a high concentration of an element

(typically a high atomization temperature element) which

cannot be removed quantitatively in one complete set of

furnace steps. The analyte which remains in the furnace

can produce false positive signals on subsequent

sample(s). Therefore, the analyst should establish the

analyte concentration which can be injected into the

furnace and adequately removed in one complete set of

furnace cycles. If this concentration is exceeded, the

sample should be diluted and a blank analyzed to assure

the memory effect has been eliminated before reanalyzing the diluted sample.

4.5 Specific Element Interferences. -- The matrix

effects caused by the saline water can be severe. In order

to evaluate the extent of the matrix suppression as a 4.5.3 Arsenic: The elevated char temperatures

function of increasing salinity a plot of normalized integrated absorbance vs. microliters NASS-3 (Reference

Material from the National Research Council of Canada)

is constructed. Figure 3 is a plot of relative response of

As, Se, Cd, Ni, Cu, and Pb in waters containing salinity of

3.5 ppt (1 μL NASS-3) to 35 ppt (10 μL NASS-3). Figure

3 indicates that the matrix effects caused by the increasing salinity are minor for Pb, Cu, and Ni. The relative

responses of Pb, Ni, and Cu shown in Figure 3 are within

± 5% of the 1% HNO standard or zero μL of matrix. 3

Figure 3 indicates that the increasing salinity does cause

a substantial matrix interference for Se and Cd. This

suppression must be compensated for by methods of

standard addition or the use of matrix matched standards

where applicable.

4.5.1 Cadmium: The background level associated with the

direct determination of Cd in NASS-3 exceeds the

Zeeman background correction. Therefore, NH4 NO3 is

used as a matrix removing modifier in addition to the Pd/

Mg(NO3)2. Figure 4 is a plot of the relative Cd response 1 

vs. the amount of seawater on the platform. A similar

the direct determination of Se in NASS-3 exceeds the

Zeeman correction capability. Therefore, HNO3 is used as

a matrix removing modifier in addition to the Pd/ Mg(NO )3 2

for the determination of Se in saline waters. Figure 5 is a

plot of relative response vs. the amount of seawater on

the platform. A similar suppression is observed in a

solution containing 10,000 ppm NaCI. Therefore, in wellcharacterized samples of known salinity it is possible to

effectively matrix match the standards with NaCl and

perform the analysis directly using matrix matched

standards, thereby avoiding the time consuming method

of standard additions. If the matrix matched standards are

going to be used, it is necessary to document that the use

of NaCl is indeed compensating for the suppression. This

documentation should include a response plot of

increasing matrix vs. relative response similar to Figure 5.

possible with the determination of As minimize the

interferences produced by the marine water background

levels. Figure 3 is a plot of relative response vs. the

amount of seawater on the platform. Figure 3 indicates a

matrix suppression on As caused by the seawater.

Although this suppression does cause a slight bias as

shown in the recovery data in Table 3, the suppression

does not warrant the method of standard additions (MSA)

given the recovery criteria of 75-125% for LFMS.

5.0 Safety

5.1 The toxicity or carcinogenicity of each reagent

used in this method has not been fully established. Each

chemical should be regarded as a potential health hazard

and exposure to these compounds should be as low as

reasonably achievable. Each laboratory is responsible for

maintaining a current awareness file of OSHA regulations

regarding the safe handling of the chemicals specified in

this method. A reference file of material data handling 2-5

sheets should also be made available to all personnel
Revision 1.0 September 1997 200.12 - 6

involved in the chemical analysis. Specifically, 6.1.2 Single element hollow cathode lamps or single

concentrated nitric and hydrochloric acids present various

hazards and are moderately toxic and extremely irritating

to skin and mucus membranes. Use these reagents in a

fume hood whenever possible and if eye or skin contact

occurs, flush with large volumes of water. Always wear

safety glasses or a shield for eye protection, protective

clothing, and observe proper mixing when working with

these reagents.

5.2 The acidification of samples containing reactive

materials may result in the release of toxic gases, such as

cyanides or sulfides. Acidification of samples should be

done in a fume hood.

5.3 All personnel handling environmental samples

known to contain or to have been in contact with human

waste should be immunized against known disease

causative agents.

5.4 The graphite tube during atomization emits intense UV radiation. Suitable precautions should be taken

to protect personnel from such a hazard.

5.5 The use of the argon/hydrogen gas mixture

during the dry and char steps may evolve a considerable

amount of HCI gas. Therefore, adequate ventilation is

required.

5.6 It is the responsibility of the user of this method to

comply with relevant disposal and waste regulations. For

guidance see Sections 14.0 and 15.0.

6.0 Equipment and Supplies

6.1 Graphite Furnace Atomic Absorption Spectrometer

6.1.1 The GFAA spectrometer must be capable of

programmed heating of the graphite tube and the

associated delayed atomization device. The instrument

must be equipped with Zeeman background correction

and the furnace device must be capable of utilizing an

alternate gas supply during specified cycles of the

analysis. The capability to record relatively fast (< 1 s)

transient signals and evaluate data on a peak area basis

is preferred. In addition, a recirculating refrigeration unit is

recommended for improved reproducibility of furnace

temperatures.

element electrodeless discharge lamps along with the

associated power supplies.

6.1.3 Argon gas supply (high-purity grade, 99.99%) for

use during the atomization of selenium, for sheathing the

furnace tube when in operation, and during furnace

cleanout. 

6.1.4 Alternate gas mixture (hydrogen 5%-argon 95%)

for use as a continuous gas flow environment during the

dry and char furnace cycles.

6.1.5 Autosampler capable of adding matrix modifier

solutions to the furnace, a single addition of analyte, and

completing methods of standard additions when required.

6.2 Analytical balance, with capability to measure to

0.1 mg, for preparing standards, and for determining

dissolved solids in digests or extracts.

6.3 A temperature adjustable hot plate capable of

maintaining a temperature of 95°C.

6.4 An air displacement pipetter capable of delivering

volumes ranging from 100 to 2500 μL with an assortment

of high quality disposable pipet tips.

6.5 Labware -- All reusable labware (glass, quartz,

polyethylene, PTFE, FEP, etc.) should be sufficiently

clean for the task objectives. Several procedures found to

provide clean labware include washing with a detergent

solution, rinsing with tap water, soaking for 4 h or more in

20% (v/v) nitric acid or a mixture of HCI and HNO3, rinsing

with reagent water and storing clean. Chromic acid

cleaning solutions must be avoided because chromium is

an analyte.

Note: Glassware having ground glass stoppers, etc.

should be avoided because the ground glass surface is

difficult to clean properly and can contain active sites

which adsorb metals.

6.5.1 Glassware -- Volumetric flasks, graduated cylinders, funnels and centrifuge tubes (glass and/or metalfree plastic).

6.5.2 Assorted calibrated pipettes.

6.5.3 Griffin beakers, 250-mL with 75-mm watch

glasses and (optional) 75-mm ribbed watch glasses.
200.12 - 7 Revision 1.0 September 1997

6.5.4 Narrow-mouth storage bottles, FEP (fluorinated that stock solutions be stored in FEP bottles. Replace

ethylene propylene) with screw closure, 125-mL to 1-L

capacities.

6.5.5 One-piece stem FEP wash bottle with screw closure, 125-mL capacity.

7.0 Reagents and Standards

7.1 Reagents may contain elemental impurities which

might affect analytical data. Only high-purity reagents that

conform to the American Chemical Society specifications6

should be used whenever possible. If the purity of a

reagent is in question, analyze for contamination. All acids

used for this method must be of ultra high-purity grade or

equivalent. Suitable acids are available from a number of

manufacturers. Redistilled acids prepared by sub-boiling

distillation are acceptable.

7.2 Nitric acid, concentrated (sp.gr. 1.41) HNO .3

7.2.1 Nitric acid (1+1) -- Add 500 mL concentrated

HNO to 400 mL reagent water and dilute to 1 L. 3

7.2.2 Nitric acid (1+5) -- Add 50 mL concentrated

HNO to 250 mL reagent water. 3

7.2.3 Nitric acid (1+9) -- Add 10 mL concentrated

HNO to 90 mL reagent water. 3

7.3 Reagent water. All references to water in this

method refer to ASTM Type I grade water.7

7.4 Ammonium hydroxide, concentrated

(sp.gr.0.902).

7.5 Matrix Modifier, dissolve 300 mg palladium (Pd)

powder in concentrated HNO3 (1 mL of HNO3, adding 10

μL of concentrated HCI if necessary). Dissolve 200 mg of

Mg(NO3)2@6H2O in ASTM Type I water. Pour the two

solutions together and dilute to 100 mL with ASTM Type

I water.

Note: It is recommended that the matrix modifier be

analyzed separately in order to assess the contribution of

the modifier to the absorbance of calibration and reagent

blank solutions.

7.6 Standard stock solutions may be purchased or

prepared from ultra-high purity grade chemicals (99.99 to

99.999% pure). All compounds must be dried for 1 h at

105EC, unless otherwise specified. It is recommended

stock standards when succeeding dilutions for preparation of calibration standards cannot be verified.

Caution: Many of these chemicals are extremely toxic if

inhaled or swallowed (Section 5.1). Wash hands thoroughly after handling.

Typical stock solution preparation procedures follow for

1-L quantities, but for the purpose of pollution prevention,

the analyst is encouraged to prepare smaller quantities

when possible. Concentrations are calculated based

upon the weight of the pure element or upon the weight

of the compound multiplied by the fraction of the analyte

in the compound.

From pure element,

Concentration = weight (mg)

volume (L)

From pure compound,

Concentration = weight (mg) x gravimetric factor

volume (L)

where:

gravimetric factor = the weight fraction of the analyte

in the compound.

7.6.1 Arsenic solution, stock, 1 mL = 1000 μg As: Dissolve 1.320 g of As2O3

 (As fraction = 0.7574), weighed

accurately to at least four significant figures, in 100 mL of

reagent water containing 10.0 mL concentrated NH OH. 4

Warm in solution gently to effect dissolution. Acidify the

solution with 20.0 mL concentrated HNO3 and dilute to

volume in a 1-L volumetric flask with reagent water.

7.6.2 Cadmium solution, stock, 1 mL = 1000 μg Cd:

Dissolve 1.000 g Cd metal, acid cleaned with (1+9) HNO ,3

weighed accurately to at least four significant figures, in

50 mL (1+1) HNO with heating to effect dissolution. Let 3

solution cool and dilute with reagent water in a 1-L

volumetric flask.

7.6.3 Chromium solution, stock, 1 mL = 1000 μg Cr:

Dissolve 1.923 g CrO3 (Cr fraction = 0.5200), weighed

accurately to at least four significant figures, in 120 mL (1

+5) HNO3. When solution is complete, dilute to volume in

a 1-L volumetric flask with reagent water.

7.6.4 Copper solution, stock, 1 mL = 1000 μg Cu: Dissolve 1.000 g Cu metal, acid cleaned with (1+9) HNO ,3
Revision 1.0 September 1997 200.12 - 8

weighed accurately to at least four significant figures, in the samples. The preparation blank must be carried

50.0 mL (1+1) HNO3 with heating to effect dissolution. Let through the entire sample digestion and preparation

solution cool and dilute in a 1-L volumetric flask with scheme.

reagent water.

7.6.5 Lead solution, stock, 1 mL = 1000 μg Pb:

Dissolve 1.599 g Pb(NO ) (Pb fraction = 0.6256), all analytes to provide a final concentration which will 3 2

weighed accurately to at least four significant figures, in a produce an absorbance of approximately 0.1 for each

minimum amount of (1+1) HNO3. Add 20.0 mL (1+1) analyte. The LFB must be carried through the complete

HNO and dilute to volume in a 1-L volumetric flask with procedure as used for the samples. 3

reagent water.

7.6.6 Nickel solution, stock, 1 mL = 1000 μg Ni:

Dissolve 1.000 g of nickel metal, weighed accurately to at the appropriate plastic containers.

least four significant figures, in 20.0 mL hot concentrated

HNO , cool, and dilute to volume in a 1-L volumetric flask 7.9 lnstrument Performance Check (IPC) Solution -- 3

with reagent water. The IPC solution is used to periodically verify instrument

7.6.7 Selenium solution, stock, 1 mL = 1000 μg Se: same acid mixture as the calibration standards by comDissolve 1.405 g SeO2

 (Se fraction = 0.7116), weighed

accurately to at least four significant figures, in 200 mL

reagent water and dilute to volume in a 1-L volumetric

flask with reagent water.

7.7 Preparation of Calibration Standards -- Fresh

calibration standards (CAL Solution) should be prepared

weekly, or as needed. Dilute each of the stock standard

solutions to levels appropriate to the operating range of

the instrument using the appropriate acid diluent. The

element concentrations in each CAL solution should be

sufficiently high to produce good measurement precision

and to accurately define the slope of the response curve.

The instrument calibration should be initially verified using

a IPC sample (Section 7.9).

7.8 Blanks -- Four types of blanks are required for

this method. A calibration blank is used to establish the

analytical calibration curve, the laboratory reagent blank

(LRB) is used to assess possible contamination from the

sample preparation procedure and to assess spectral

background, the laboratory fortified blank is used to

assess routine laboratory performance, and a rinse blank

is used to flush the instrument autosampler uptake system. All diluent acids should be made from concentrated

acids (Section 7.2) and ASTM Type I water.

7.8.1 The calibration blank consists of the appropriate

acid diluent in ASTM Type I water. The calibration blank

should be stored in a FEP bottle.

7.8.2 The laboratory reagent blanks must contain all

the reagents in the same volumes as used in processing

7.8.3 The laboratory fortified blank (LFB) is prepared

by fortifying an aliquot of the laboratory reagent blank with

7.8.4 The rinse blank is a 0.1% HCI and 0.1% HNO3

solution used to flush the autosampler tip and is stored in

performance during analysis. It should be prepared in the

bining method analytes at appropriate concentrations to

approximate the midpoint of the calibration curve. The

IPC solution should be prepared from the same standard

stock solutions used to prepare the calibration standards

and stored in a FEP bottle. Agency programs may specify

or request that additional instrument performance check

solutions be prepared at specified concentrations in order

to meet particular program needs.

7.10 Quality Control Sample (QCS) -- For initial and

periodic verification of calibration standards and instrument performance, analysis of a QCS is required. The

QCS must be obtained from an outside source different

from the standard stock solutions and prepared in the

same acid mixture as the calibration standards. The

concentration of the analytes in the QCS solution should

be such that the resulting solution will provide an absorbance reading of approximately 0.1. The QCS solution

should be stored in a FEP bottle and analyzed as needed

to meet data-quality needs. A fresh solution should be

prepared quarterly or as needed.

7.11 Matrix Performance Check (MPC) -- The MPC

solution is used to periodically evaluate the laboratory/

instrument performance in saline samples. It should be

prepared in the same acid mixture as the calibration

standards by combining method analytes at appropriate

concentrations in a seawater matrix (NASS-3, or its

equivalent) to produce an absorbance of 0.1. The MPC

solution should be prepared from the same standard

stock solutions used to prepare the calibration standards

and stored in a FEP bottle. The MPC sample should be

analyzed after every 10 samples to assure saline matrix

is not producing false positives.
200.12 - 9 Revision 1.0 September 1997

8.0 Sample Collection, Preservation and

Storage

8.1 Prior to collection of an aqueous sample,

consideration should be given to the type of data required.

Acid preservation should be performed at the time of

sample collection or as soon thereafter as practically

possible. The pH of all aqueous samples must be tested

immediately prior to aliquoting for analysis to ensure the

sample has been properly preserved. If properly acidpreserved, the sample can be held up to 6 months before

analysis.

8.2 For determination of total recoverable elements

in aqueous samples, acidify with (1+1) nitric acid at the

time of collection to pH<2. Normally, 3 mL of (1+1) nitric

acid (ultra high purity) per liter of sample is sufficient for

most ambient water samples. The sample should not be

filtered prior to analysis.

Note: Samples that cannot be acid-preserved at the

time of collection because of sampling limitations or

transport restrictions, or are > pH 2 because of high

alkalinity should be acidified with nitric acid to pH < 2 upon

receipt in the laboratory. Following acidification, the

sample should be held for 16 h and the pH verified to be

<2 before withdrawing an aliquot for sample processing.

8.3 For aqueous samples, a field blank should be

prepared and analyzed as required by the data user. Use

the same container and acid as used in sample collection.

9.0 Quality Control

9.1 Each laboratory using this method is required to

operate a formal quality control (QC) program. The

minimum requirements of this program consist of an initial

demonstration of laboratory capability, and the periodic

analysis of laboratory reagent blanks, fortified blanks and

other laboratory solutions as a continuing check on

performance. The laboratory is required to maintain

performance records that define the quality of the data

thus generated.

9.2 Initial Demonstration of Performance 

(Mandatory)

9.2.1 The initial demonstration of performance is used

to characterize instrument performance (determination of

linear dynamic ranges and analysis of quality control

samples) and laboratory performance (determination of

method detection limits) prior to samples being analyzed

by this method.

9.2.2 Linear dynamic range (LDR) -- The upper limit of

the LDR must be established for the wavelength utilized

for each analyte by determining the signal responses

from a minimum of six different concentration standards

across the range, two of which are close to the upper limit

of the LDR. Determined LDRs must be documented and

kept on file. The linear calibration range which may be

used for the analysis of samples should be judged by the

analyst from the resulting data. The upper LDR limit

should be an observed signal no more than 10% below

the level extrapolated from the four lower standards. New

LDRs should be determined whenever there is a

significant change in instrument response, a change in

instrument analytical hardware or operating conditions.

Note: Multiple cleanout furnace cycles may be necessary in order to fully define or utilize the LDR for certain

elements such as chromium. For this reason, the upper

limit of the linear calibration range may not correspond to

the upper operational LDR limit.

Measured sample analyte concentrations that exceed the

upper limit of the linear calibration range must either be

diluted and reanalyzed (with concern for memory effects

Section 4.4) or analyzed by another approved method.

9.2.3 Quality control sample (QCS) -- When beginning

the use of this method, on a quarterly basis or as required

to meet data-quality needs, verify the calibration standards and acceptable instrument performance with the

preparation and analyses of a QCS (Section 7.10). If the

determined concentrations are not within ± 10% of the

stated values, performance of the determinative step of

the method is unacceptable. The source of the problem

must be identified and corrected before either proceeding

on with the initial determination of method detection limits

or continuing with ongoing analyses.

9.2.4 Method detection limit (MDL) -- MDLs must be

established for all analytes, using reagent water (blank)

fortified at a concentration of two to three times the

estimated instrument detection limit. To determine MDL 8

values, take seven replicate aliquots of the fortified

reagent water and process through the entire analytical

method. Perform all calculations defined in the method

and report the concentration values in the appropriate

units. Calculate the MDL as follows:
Revision 1.0 September 1997 200.12 - 10

MDL = (t) x (S) outside the required control limits of 85-115%, that

where, t = Student's t value for a 99% confidence level problem should be identified and resolved before

and a standard deviation estimate with n-1 degrees of continuing analyses.

freedom [t = 3.14 for seven replicates].

S = standard deviation of the replicate analyses.

Note: If the percent relative standard deviation (% RSD)

from the analyses of the seven aliquots is < 15%, the

concentration used to determine the analyte MDL may

have been inappropriately high for the determination. If

so, this could result in calculation of an unrealistically low

MDL. If additional confirmation of the MDL is desired,

reanalyze the seven replicate aliquots on two more

nonconsecutive days and again calculate the MDL values

for each day. An average of the three MDL values for

each analyte may provide a more appropriate MDL

estimate. Concurrently, determination of MDL in reagent

water represents a best case situation and does not

reflect possible matrix effects of real world samples.

However, successful analyses of LFMs (Section 9.4) and

the analyte addition test described in Section 9.5.1 can

give confidence to the MDL value determined in reagent

water. Typical single laboratory MDL values using this

method are given in Table 2.

MDLs should be determined every six months, when a

new operator begins work or whenever there is a signifi- 9.3.4 Instrument performance check (IPC) solution --

cant change in the background or instrument response.

The MDLs reported in Table 2 were determined in fortified NASS-3 samples. It is recommended that a certified

saline matrix such as NASS-3 be used to determine

MDLS.

9.3 Assessing Laboratory Performance (Mandatory)

9.3.1 Laboratory reagent blank (LRB) -- The laboratory

must analyze at least one LRB (Section 7.8.2) with each firms calibration to be outside the limits, sample analysis

batch of 20 or fewer samples. LRB data are used to must be discontinued, the cause determined and/or, in

assess contamination from the laboratory environment. the case of drift, the instrument recalibrated. All samples

LRB values that exceed the MDL indicate laboratory or following the last acceptable IPC solution must be reanareagent contamination should be suspected. Any deter- lyzed. Data for the calibration blank and IPC solution

mined source of contamination must be corrected and the must be kept on file with associated sample data.

samples reanalyzed for the affected analytes after

acceptable LRB values have been obtained. 9.3.5 Matrix performance check (MPC) solution -- For

9.3.2 Laboratory fortified blank (LFB) -- The laboratory

must analyze at least one LFB (Section 7.8.3) with each bration, after every tenth sample (or more frequently, if

batch of samples. Calculate accuracy as percent recov- required) and after the last sample in the batch is anaery (Section 9.4.3). If the recovery of any analyte falls lyzed. Analysis of the MPC must verify that the instrument

analyte is judged out of control, and the source of the

9.3.3 The laboratory must use LFB analyses data to

assess laboratory performance against the required

control limits of 85-115%. When sufficient internal performance data become available (usually a minimum of 20-

30 analyses), optional control limits can be developed

from the percent mean recovery (x) and the standard

deviation (S) of the mean recovery. These data can be

used to establish the upper and lower control limits as

follows:

Upper Control Limit = x + 3S

Lower Control Limit = x - 3S

The optional control limits must be equal to or better than

the required control limits of 85-115%. After each five to

ten new recovery measurements, new control limits can

be calculated using only the most recent 20-30 data

points. Also, the standard deviation (S) data should be

used to establish an ongoing precision statement for the

level of concentrations included in the LFB. These data

must be kept on file and be available for review.

For all determinations the laboratory must analyze the

IPC solution (Section 7.9) and a calibration blank

immediately following daily calibration, after every tenth

sample (or more frequently, if required) and after the last

sample in the batch is analyzed. Analysis of the I PC

solution and calibration blank immediately following

calibration must verify that the instrument is within ± 5% of

calibration. Subsequent analyses of the IPC solution must

verify the calibration within ± 10%. If the calibration cannot

be verified within the specified limits, reanalyze the IPC

solution. If the second analysis of the IPC solution conall determinations, the laboratory must analyze the MPC

solution (Section 7.11) immediately following daily cali-
200.12 - 11 Revision 1.0 September 1997

is within ± 15% of calibration and confirm that the matrix 9.4.4 If the recovery of any analyte falls outside the

is not causing matrix/background interferences. If the

MPC is not within ± 15%, reanalyze the MPC solution. If

the second analysis of the MPC solution is outside the

limits, sample analysis must be discontinued the cause

determined and/or, in the case of drift, the instrument

recalibrated. All samples following the last acceptable

MPC solution must be reanalyzed. The analysis data for

the calibration blank and MPC solution must be kept on

file with the sample analyses data.

9.4 Assessing Analyte Recovery and Data Quality

9.4.1 Sample homogeneity and the chemical nature of

the sample matrix can affect analyte recovery and the recovery of the LFM should be calculated. If the fortified

data quality. Taking separate aliquots from the sample for analyte in the diluted LFM is found to be < 25% of the

replicate and fortified analyses can in some cases assess sample concentration or the diluted LFM produces an

these effects. Unless otherwise specified by the data user, atomic signal of <10 times the MDL, the diluted sample

laboratory or program, the following laboratory fortified should be analyzed by methods of standard addition. If

matrix (LFM) procedure (Section 9.4.2) is required. Also, the calculated recovery of the diluted sample is within the

the analyte addition test (Section 9.5.1) can aid in designated range, the sample concentration should be

identifying matrix interferences. However, all samples calculated from the diluted sample. If the calculated

must have a background absorbance < 1.0 before the recovery of the diluted sample is outside the designated

test results obtained can be considered reliable. range, follow the directions given below. If the back9.4.2 The laboratory must add a known amount of dilution, all samples of a similar matrix should be diluted

each analyte to a minimum of 10% of the routine

samples. In each case the LFM aliquot must be a

duplicate of the aliquot used for sample analysis and for

total recoverable determinations added prior to sample

preparation. For water samples, the added analyte

concentration must be the same as that used in the

laboratory fortified blank (Section 9.3.2).

9.4.3 Calculate the percent recovery for each analyte,

corrected for concentrations measured in the unfortified

sample, and compare these values to the designated

LFM recovery range of 75-125%. Recovery calculations

are not required if the concentration added is less than

25% of the unfortified sample concentration. Percent

recovery may be calculated in units appropriate to the

matrix, using the following equation:

R = Cs - C x 100

s

where, R = percent recovery.

C = fortified sample concentration. s

C = sample background concentration.

s = concentration equivalent of analyte

added to sample.

designated LFM recovery range (but is still within the

range of calibration and the background absorbance is <

1.0 abs.) and the laboratory performance for that analyte

is shown to be in control (Section 9.3), the recovery

problem encountered with the LFM is judged to be either

matrix or solution related, not system related. A flowchart

of the remainder of this section can be found in Figure 6.

This flowchart may clarify the verbal discussion given

below.

If the background absorbance is > 1 abs., the sample and

the LFM should be diluted 1:3 and reanalyzed until the

background absorbance is < 1, at which point a percent

ground is reduced and/or the matrix effect is reduced by

and analyzed in a similar fashion. The result should be

flagged indicating the methods sensitivity has been reduced by the dilution. If dilution is unacceptable because

of data quality objectives the sample should be flagged

indicating the analysis is not possible via this analytical

procedure.

If the analyte recovery on the LFM is <75% and the

background absorbance is <1, complete the analyte

addition test (Section 9.5.1) on the original sample (or its

dilution). The results of the test should be evaluated as

follows:

1. If recovery of the analyte addition test (< 85%)

confirms a low recovery for the LFM, a suppressive

matrix interference is indicated and the unfortified

sample aliquot must be analyzed by method of

standard additions (Section 11.3).

2. If the recovery of the analyte addition test is between

85% to 115%, a low recovery of the analyte in the

LFM (< 75%) may be related to the heterogeneity of

the sample, sample preparation or a poor transfer,

etc. Report the sample concentration based on the

unfortified sample aliquot.
Revision 1.0 September 1997 200.12 - 12

3. If the recovery of the analyte addition test is less prevents successful determination of the analyte or when

than recovery calculated for the LFM, matrix sup- the heterogeneous nature of the sample precludes the

pression is confirmed. The unfortified sample use of duplicate analyses.

should be analyzed by MSA (Section 11.3).

Significantly lower recoveries (relative to the LFM) 9.4.6 Where reference materials are available, they

associated with the analyte addition test are

unlikely unless the sample is heterogeneous.

4. If the recovery of the analyte addition test is >115%,

the dramatic change in analyte response should be

verified by fortifying the LFM. The recovery in the

sample and the recovery in the LFM should be

compared. If the recoveries verify the dramatic

response difference, the sample results should be

flagged indicating the sample matrix is not homogeneous.

If the analyte recovery in the LFM is > 125% and the

background absorbance is < 1, complete the analyte

addition test (Section 9.5.1) on the unfortified sample (or

its dilution) aliquot.

1 . If the percent recovery of the analyte addition test is

> 115% and the LFB does not indicate laboratory

contamination, an enhancing matrix interference

(albeit rare) is indicated, and the unfortified sample

aliquot must be analyzed by method of standard

additions (Section 11.3).

2. If the percent recovery of the analyte addition test is

between 85% to 115%, either random sample contamination of the LFM, an incorrect analyte concentration was added to the LFM prior to sample

preparation, or sample heterogeneity should be

suspected. Report analyte data determined from the

analysis of the unfortified sample aliquot.

3. If the percent recovery of the analyte addition test is

< 85%, a heterogeneous sample with matrix interference is suspected. This dramatic change in response should be verified by performing the analyte

addition test to the LFM. The recovery in the sample

and the recovery in the LFM should be compared. If

the recoveries verify the dramatic response difference the sample results should be flagged indicating

the sample matrix is not homogeneous.

9.4.5 If the analysis of a LFM sample(s) and the test

routines above indicate an operative interference and the

LFMs are typical of the other samples in the batch, those

samples that are similar must be analyzed in the same

manner as the LFMS. Also, the data user must be

informed when a matrix interference is so severe that it

should be analyzed to provide additional performance

data. Analysis of reference samples is a valuable tool for

demonstrating the ability to perform the method acceptably. It is recommended that NASS-3 or its equivalent be

fortified and used as an MPC.

9.5 Matrix interference effects and the need for MSA

can be assessed by the following test. Directions for using

MSA are given in Section 11.3.

9.5.1 Analyte addition test: An analyte standard added

to a portion of a prepared sample or its dilution should be

recovered to within 85-115% of the known value. The

analyte addition should occur directly to sample in the

furnace and should produce a minimum absorbance of

0.1. The concentration of the analyte addition plus that in

the sample should not exceed the linear calibration range

of the analyte. If the analyte is not recovered within the

specified limits, a matrix effect should be suspected and

the sample must be analyzed by MSA.

10.0 Calibration and Standardization

10.1 Specific wavelengths and instrument operating

conditions are listed in Table 1. However, because of

differences among makes and models of spectrophotometers and electrothermal furnace devices, the actual

instrument conditions selected may vary from those listed.

10.2 Prior to the use of this method, the instrument

operating conditions must be optimized. The analyst

should follow the instructions provided by the manufacturer while using the conditions listed in Table 1 as a

guide. The appropriate charring condition for each of the

analytes is a critical part of the metal analysis in saline

waters; therefore, the char temperature profiles should be

determined in a saline water matrix. The appropriate

charring temperature should be chosen so as to minimize

background absorbance while providing some furnace

temperature variation without the loss of analyte. For

analytical operation, the charring temperature is usually

set at least 100EC below the point at which analyte begins

to be lost during the char. Because the background

absorbance can be affected by the atomization temperature, care should be taken in the choice of an appropriate

atomization temperature. The optimum conditions se-
200.12 - 13 Revision 1.0 September 1997

lected should provide the lowest reliable MDLs and be 11.1.3 Cover the lip of the beaker with a watch glass to

similar to those listed in Table 2. Once the optimum

operating conditions are determined, they should be

recorded and available for daily reference. The effectiveness of these operating conditions are continually evaluated by analyzing the MPC.

10.3 Prior to an initial calibration the linear dynamic

range of the analyte must be determined (Sect 9.2.2)

using the optimized instrument operating conditions. For

all determinations allow an instrument and hollow cathode lamp warm-up period of not less than 15 min. If an

EDL is to be used, allow 30 min for warm-up.

10.4 Before using the procedure (Section 11.0) to analyze samples, there must be data available documenting

initial demonstration of performance. The required data

and procedure are described in Section 9.2. This data

must be generated using the same instrument operating

conditions and calibration routine to be used for sample

analysis. These documented data must be kept on file

and be available for review by the data user.

11.0 Procedure

11.1 Aqueous Sample Preparation -- Total Recoverable Analytes

11.1.1 Add 2 mL (1+1) nitric acid to the beaker

containing 100 mL of sample. Place the beaker on a hot

plate for solution evaporation. The hot plate should be

located in a fume hood and previously adjusted to provide

evaporation at a temperature of approximately but no

higher than 85EC. (See the following note.) The beaker

should be covered with an elevated watch glass or other

necessary steps should be taken to prevent sample

contamination from the fume hood environment.

Note: For proper heating adjust the temperature control

of the hot plate such that an uncovered Griffin beaker

containing 50 mL of water placed in the center of the hot

plate can be maintained at a temperature approximately

but no higher than 85EC. (Once the beaker is covered

with a watch glass the temperature of the water will rise

to approximately 95EC.)

11.1.2 Reduce the volume of the sample aliquot to

about 20 mL by gentle heating at 85EC. DO NOT BOIL.

This step takes about 2 h for a 100-mL aliquot with the

rate of evaporation rapidly increasing as the sample

volume approaches 20 mL. (A spare beaker containing

20 mL of water can be used as a gauge.)

reduce additional evaporation and gently reflux the

sample for 30 min.

11.1.4 Allow the beaker to cool. Quantitatively transfer

the sample solution to a 100-mL volumetric flask, dilute

to volume with reagent water, stopper and mix.

11.1.5 Allow any undissolved material to settle overnight, or centrifuge a portion of the prepared sample until

clear. (If after centrifuging or standing overnight the

sample contains suspended solids, a portion of the

sample may be filtered prior to analysis. However, care

should be exercised to avoid potential contamination from

filtration.) The sample is now ready for analysis. Because

the effects of various matrices on the stability of diluted

samples cannot be characterized, all analyses should be

performed as soon as possible after the completed

preparation.

11.2 Sample Analysis

11.2.1 Prior to daily calibration of the instrument, inspect the graphite tube and contact rings for salt

buildup, etc. Generally, it will be necessary to clean the

contact rings and replace the graphite tube daily. The

contact rings are a cooler environment in which salts

can deposit after atomization. A cotton swab dipped in a

50/50 mixture of isopropyl alcohol (IPA) and H2O (such

that it is damp but not dripping) can be used to remove

the majority of the salt buildup. A second cotton swab is

dipped in IPA and the contact rings are wiped down to

assure they are clean. The rings are then allowed to

thoroughly dry and then a new tube is placed in the

furnace and conditioned according to instrument

manufacturer's specifications.

11.2.2 Configure the instrument system to the selected

optimized operating conditions as determined in Sections

10.1 and 10.2.

11.2.3 Before beginning daily calibration the instrument

should be reconfigured to the optimized conditions. Initiate the data system and allow a period of not less than

15 min for instrument and hollow cathode lamp warm up.

If an EDL is to be used, allow 30 min for warm up.

11.2.4 After the warm up period but before calibration,

instrument stability must be demonstrated by analyzing a

standard solution with a concentration 20 times the IDL a

minimum of five times. The resulting relative standard

deviation of absorbance signals must be < 5%. If the
Cx'

SBVSCS

(SA&SB)VX

Revision 1.0 September 1997 200.12 - 14

relative standard deviation is > 5%, determine and correct 11.2.11 When it is necessary to assess an operative

the cause before calibrating the instrument.

11.2.5 For initial and daily operation, calibrate the instrument according to the instrument manufacturer's

recommended procedures using the calibration blank 11.2.12 Report data as directed in Section 12.

(Section 7.8.1) and calibration standards (Section 7.7)

prepared at three or more concentrations within the

usable linear dynamic range of the analyte (Sections 4.4

and 9.2.2).

11.2.6 An autosampler must be used to introduce all

solutions into the graphite furnace. Once the sample and

the matrix modifier are injected, the furnace controller

completes a set of furnace cycles and a cleanout period

as programmed. Analyte signals must be reported on an

integrated absorbance basis. Background absorbances,

background heights and the corresponding peak profiles

should be displayed to the CRT for review by the analyst

and be available as hard copy for documentation to be

kept on file. Flush the autosampler solution uptake system with the rinse blank (Section 7.8.4) between each

solution injected.

11.2.7 After completion of the initial requirements of

this method (Section 9.2), samples should be analyzed

in the same operational manner used in the calibration

routine.

11.2.8 During sample analyses, the laboratory must

comply with the required quality control described in

Sections 9.3 and 9.4.

11.2.9 For every new or unusual matrix, when practical, where, S and S are the analytical signals (corrected

it is highly recommended that an inductively coupled

plasma atomic emission spectrometer be used to screen

for high element concentration. Information gained from

this may be used to prevent potential damage to the

instrument and to better estimate which elements may

require analysis by graphite furnace.

11.2.10 Determined sample analyte concentrations that

are > 90% of the upper limit of calibration must either

be diluted with acidified reagent water and reanalyzed

with concern for memory effects (Section 4.4), or

determined by another approved but less sensitive

procedure. Samples with background absorbances > 1

must be diluted with appropriate acidified reagent water

such that the background absorbance is < 1 (Section

9.4.4). If the method of standard additions is required,

follow the instructions described in Section 11.3.

matrix interference (e.g., signal reduction due to high

dissolved solids), the test described in Section 9.5 is

recommended.

11.3 Standard Additions -- If the method of standard

addition is required, the following procedure is recommended:

11.3.1 The standard addition technique involves pre9

paring new standards in the sample matrix by adding

known amounts of standard to one or more aliquots of the

processed sample solution. This technique compensates

for a sample constituent that enhances or depresses the

analyte signal, thus producing a different slope from that

of the calibration standards. It will not correct for additive

interference, which causes a baseline shift. The simplest

version of this technique is the single-addition method.

The procedure is as follows: Two identical aliquots of the

sample solution, each of volume V , are taken. To the first x

(labeled A) is added a small volume VS of a standard

analyte solution of concentration CS. To the second

(labeled B) is added the same volume VS of the solvent.

The analytical signals of A and B are measured and

corrected for nonanalyte signals. The unknown sample

concentration CX is calculated:

A B

for the blank) of solutions A and B, respectively. VS and

CS should be chosen so that SA is roughly twice SB on

the average. It is best if VS is made much less than VX,

and thus CS is much greater than CX, to avoid excess

dilution of the sample matrix. If a separation or

concentration step is used, the additions are best made

first and carried through the entire procedure. For the

results from this technique to be valid, the following

limitations must be taken into consideration:

1. The analytical curve must be linear.

2. The chemical form of the analyte added must respond in the same manner as the analyte in the

sample.

3. The interference effect must be constant over the

working range of concern.
200.12 - 15 Revision 1.0 September 1997

4. The signal must be corrected for any additive inter- EPA has established a preferred hierarchy of environference. mental management techniques that places pollution

12.0 Data Analysis and Calculations

12.1 Sample data should be reported in units of Fg/L

for aqueous samples.

12.2 For total recoverable aqueous analytes (Section

11.1), when 100-mL aliquot is used to produce the 100

mL final solution, round the data to the tenths place and

report the data in Fg/L up to three significant figures. If a

different aliquot volume other than 100 mL is used for

sample preparation, adjust the dilution factor accordingly.

Also, account for any additional dilution of the prepared

sample solution needed to complete the determination of

analytes exceeding the upper limit of the calibration curve.

Do not report data below the determined analyte MDL

concentration or below an adjusted detection limit

reflecting smaller sample aliquots used in processing or 15.1 The Environmental Protection Agency requires

additional dilutions required to complete the analysis. that laboratory waste management practices be con12.3 The QC data obtained during the analyses tions. The Agency urges laboratories to protect the air,

provide an indication of the quality of the sample data and water, and land by minimizing and controlling all releases

should be provided with the sample results. from hoods and bench operations, complying with the

13.0 Method Performance

13.1 Instrument operating conditions used for single

laboratory testing of the method and MDLs are listed in

Tables 1 & 2.

13.2 Table 3 contains precision and recovery data obtained from a single laboratory analysis of four fortified

sample replicates of NASS-3. Five unfortified replicates

were analyzed, and their average concentration was used

to determine the sample concentration. Samples were

prepared using the procedure described in Section 11.1.

Four samples were fortified at the levels reported in Table

3. Average percent recovery and percent relative

standard deviation are reported in Table 3 for the fortified

samples.

14.0 Pollution Prevention

14.1 Pollution prevention encompasses any technique

that reduces or eliminates the quantity or toxicity of waste

at the point of generation. Numerous opportunities for

pollution prevention exist in laboratory operation. The

prevention as the management option of first choice.

Whenever feasible, laboratory personnel should use

pollution prevention techniques to address their waste

generation. When wastes cannot be feasibly reduced at

the source, the Agency recommends recycling as the

next best option.

14.2 For information about pollution prevention that

may be applicable to laboratories and research institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction, available from the American Chemical Society's Department of Government

Relations and Science Policy, 1155 16th Street N.W.,

Washington D.C. 20036, (202)872-4477.

15.0 Waste Management

ducted consistent with all applicable rules and regulaletter and spirit of any sewer discharge permits and

regulations, and by complying with all solid and hazardous waste regulations, particularly the hazardous waste

identification rules and land disposal restrictions. For

further information on waste management consult The

Waste Management Manual for Laboratory Personnel,

available from the American Chemical Society at the

address listed in the Section 14.2.

16.0 References

1. Pruszkowska, E., G. Carnrick, and W. Slavin. Anal.

Chem. 55,182-186,1983.

2. Carcinogens - Working With Carcinogens,

Department of Health, Education, and Welfare,

Public Health Service, Centers for Disease Control,

National Institute for Occupational Safety and

Health, Publication No. 77-206, Aug. 1977.

3. OSHA Safety and Health Standards, General

Industry, (29 CFR 1910), Occupational Safety and

Health Administration, OSHA 2206, (Revised,

January 1976).
Revision 1.0 September 1997 200.12 - 16

4. Safety in Academic Chemistry Laboratories,

American Chemical Society Publication,

Committee on Chemical Safety, 3rd Edition, 1979.

5. Proposed OSHA Safety and Health Standards,

Laboratories, Occupational Safety and Health

Administration, Federal Register, July 24,1986.

6. Rohrbough, W.G. et al. Reagent Chemicals,

American Chemical Society Specifications, 7th

edition. American Chemical Society, Washington,

DC, 1986.

7. American Society for Testing and Materials.

Standard Specification for Reagent Water, D1193-

77. Annual Book of ASTM Standards, Vol. 11.01.

Philadelphia, PA, 1991.

8. Code of Federal Regulations 40, Ch. 1, Pt. 136,

Appendix B.

9. Winefordner, J.D., Trace Analysis: Spectroscopic

Methods for Elements, Chemical Analysis, Vol. 46,

pp. 41-42, 1976.
200.12 - 17 Revision 1.0 September 1997

17.0 Tables, Diagrams, Flowcharts, and Validation Data

Table 1. Furnace Conditions for Determination of Metals in Seawater 1

Element Wavelength (nm) Method of Furnaces Temp Temp 5

Slit Width (nm) Analysis Modifier Cycle EC Ramp Hold Time (sec) 2,3

As 193.7 Direct Pd/Mg Dry 130 1 60

0.7 Char 1400 10 60 4

Atomization 2200 0 5

Cd 228.8 Matrix Match Pd/Mg Dry 130 1 60

0.7 Standard + Char 1 350 45 30

or 600 Fg Char 2 850 1 30

 Std. Addition NH4NO3 Atomization 1500 0 5

Cr 357.9 Direct Pd/Mg Dry 130 1 60

0.7 Char 1500 5 30

 Atomization 2600 0 5

Cu 324.8 Direct Pd/Mg Dry 130 1 60

0.7 Char 1300 10 30

Atomization 2600 0 5

Ni 232.4 Direct Pd/Mg Dry 130 1 60

0.2 Char 1400 10 30 4

Atomization 2600 0 7

Pb 283.3 Direct Pd/Mg Dry 130 1 60

0.7 Char 1200 10 45

Atomization 2200 0 5

 Se 196.0 Matrix Match Pd/Mg Dry 130 1 60

2.0 Standard 9% HNO3 on Char 1000 5 60

or Platform Atomization 2100 0 5

Std. Addition

 10-FL sample size. 1

 5FL of (30 mg Pd Powder and 20 mg Mg(NO ) @6H O to 10 mL). 2

3 2 2

 A gas mixture of 5% H in 95% Ar is used during the dry and char. 3

2

 Sodium emission is visibly exiting from the sample inlet port. 4

 The furnace program has a cool down step of 20E between char and atomization and a clean out step of 2600E C after atomization. 5

Table 2. MDLs and Background Absorbances Associated with a Fortified NASS-31-3

Typical

Integrated

MDL Background 5

Element Fg/L Absorbances6

Cd 0.1 1.2

Cr - 0.2

Cu 2.8 0.2

Ni 1.8 0.1

Pb 2.4 0.4

Se 9.5 1.4 4

As 2.6 0.3 4

 Matrix Modifier = 0.015 mg Pd + 0.01 mg Mg(NO ) .

1

3 2

 A 5% H in Ar gas mix is used during the dry and char steps at 300 mL/min for all elements. 2

2

 10-FL sample size. 3

 An electrodeless discharge lamp was used for this element. 4

 MDL calculated based on fortifying NASS-3 with metal analytes. 5

 Background absorbances are affected by the atomization temperature for analysis, therefore, lowering atomization temperatures may be 6

advantageous if large backgrounds are observed.

- Not Determined.
Revision 1.0 September 1997 200.12 - 18

Table 3. Precision and Recovery Data for Fortified NASS-3

Certified Observed Fortified Fortified

Value Value Conc. Avg. Conc. Avg.

Element Fg/L Fg/L Fg/L Recovery, % %RSD Fg/L Recovery, % % RSD 2

As 1.65 ± 0.19 < MDL 15 89 3.6 37.5 85 1.6

Cd 0.029 ± 0.004 < MDL 1.0 107 4.5 2.5 104 3.8 1

Cr 0.175 ± 0.010 < MDL 5 88 0.7 12.5 85 1.6

Cu 0.109 ± 0.011 < MDL 15 95 4.4 37.5 91 0.9

Pb 0.039 ± 0.006 < MDL 15 103 2.3 37.5 99 3.4

Ni 0.257 ± 0.027 < MDL 15 92 10.1 37.5 93 7.1

Se 0.024 ± 0.004 < MDL 25 101 2.9 62.5 99 3.9 1

 Standards were made in 10,000 ppm NaCl for this analysis. 1

 Determined from four sample replicates. 2
200.12 - 19 Revision 1.0 September 1997
Revision 1.0 September 1997 200.12 - 20
200.12 - 21 Revision 1.0 September 1997