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
200.12-1
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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:
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
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 work-
ing 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
120°C) 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 concomi-
tant 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 element-
specific 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 nonspe-
cific component associated with the actual analyte ab-
sorbance, Zeeman background correction is required to
subtract from the total signal the component which is
nonspecific to the analyte. In the absence of interfer-
ences, 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 instru-
ment response caused by the sample matrix must be
corrected for by the method of standard addition (Section
11.3).
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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 pre-
pared from the primary dilution standard solution or stock
standard solutions and the internal standards and surro-
gate analytes. The CAL solutions are used to calibrate the
instrument response with respect to analyte concen-
tration.
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 mini-
mum 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 se-
lected 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 concentra-
tions.
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 interfer-
ences 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 pre-
cautions.
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 forti-
fied 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, mea-
sured 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
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different from the source of calibration standards. It is
used to check laboratory performance with externally
prepared test materials.
3.16 Standard Addition - The addition of a known
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 concen-
trated 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 con-
centration of analyte determined to be in either a solid
sample or an unfiltered aqueous sample following treat-
ment 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 wave-
length 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 un-
wanted 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
suggested matrix modifiers and the appropriate furnace
charring conditions. Figure 1 is a plot of integrated
background absorbance vs. char temperature for Ni, Cd,
Pb, and Se. Figure 1 indicates that the background
absorbance in a saline matrix is strongly affected by the
char temperature. Therefore, char temperature optimi-
zation 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 800°C 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 atomi-
zation 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 cop-
per 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 com-
ponents 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
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200.12-4
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phase environment during atomization is required. These
devices provide an environment which is more conducive
to the formation of free analyte atoms and thereby
minimize this type of interference. This type of
interference can be detected by analyzing the sample
plus a sample aliquot fortified with a known concentration
of the analyte. If the determined concentration of the
analyte addition is outside a designated range (Section
9.4.3), a possible matrix effect should be suspected. In
addition, the matrix can produce analyte complexes which
are lost via volatilization during the char. These losses will
result in poor recovery of the analyte within the matrix and
should be corrected by adjusting the char temperature.
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 reanalyz-
ing 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
function of increasing salinity a plot of normalized inte-
grated 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 |jL NASS-3) to 35 ppt (10 |jl_ NASS-3). Figure
3 indicates that the matrix effects caused by the increas-
ing 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% HN03 standard or zero |jL of matrix.
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 N03 is
used as a matrix removing modifier in addition to the Pd/
Mg(N03)2.1 Figure 4 is a plot of the relative Cd response
vs. the amount of seawater on the platform. A similar
response profile is observed in a solution containing
10,000 ppm NaCI. Therefore, in well-characterized
samples of known salinity it is possible to effectively matrix
match the standards with NaCI 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 NaCI is indeed
compensating for the suppression. This documentation
should include a response plot of increasing matrix vs.
relative response similar to Figure 4.
4.5.2 Selenium: The background level associated with
the direct determination of Se in NASS-3 exceeds the
Zeeman correction capability. Therefore, HN03 is used as
a matrix removing modifier in addition to the Pd/ Mg(N03)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 well-
characterized samples of known salinity it is possible to
effectively matrix match the standards with NaCI and
perform the analysis directly using matrix matched
standards, thereby avoiding the time consuming method
of standard additions. Ifthe matrix matched standards are
going to be used, it is necessary to document that the use
of NaCI is indeed compensating for the suppression. This
documentation should include a response plot of
increasing matrix vs. relative response similar to Figure 5.
4.5.3 Arsenic: The elevated char temperatures
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.2"5 A reference file of material data handling
sheets should also be made available to all personnel
200.12-5
Revision 1.0 September 1997
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involved in the chemical analysis. Specifically,
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 in-
tense 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 Spec-
trometer
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.
6.1.2 Single element hollow cathode lamps or single
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 |jL 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 HN03, 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 cylin-
ders, funnels and centrifuge tubes (glass and/or metal-
free 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.
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6.5.4 Narrow-mouth storage bottles, FEP (fluorinated
ethylene propylene) with screw closure, 125-mL to 1-L
capacities.
6.5.5 One-piece stem FEP wash bottle with screw clo-
sure, 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) HN03.
7.2.1 Nitric acid (1+1) Add 500 mL concentrated
HN03 to 400 mL reagent water and dilute to 1 L.
7.2.2 Nitric acid (1+5) Add 50 mL concentrated
HN03 to 250 mL reagent water.
7.2.3 Nitric acid (1+9) Add 10 mL concentrated
HN03 to 90 mL reagent water.
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 HN03 (1 mL of HN03, adding 10
|jL of concentrated HCI if necessary). Dissolve 200 mg of
Mg(N03)2-6H20 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
105°C, unless otherwise specified. It is recommended
that stock solutions be stored in FEP bottles. Replace
stock standards when succeeding dilutions for prepara-
tion of calibration standards cannot be verified.
Caution: Many of these chemicals are extremely toxic if
inhaled or swallowed (Section 5.1). Wash hands thor-
oughly 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 (ma)
volume (L)
From pure compound,
Concentration = weight (mol 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 |jg As: Dis-
solve 1.320 g of As203 (As fraction = 0.7574), weighed
accurately to at least four significant figures, in 100 mL of
reagent water containing 10.0 mL concentrated NH4OH.
Warm in solution gently to effect dissolution. Acidify the
solution with 20.0 mL concentrated HN03 and dilute to
volume in a 1-L volumetric flask with reagent water.
7.6.2 Cadmium solution, stock, 1 mL = 1000 |jg Cd:
Dissolve 1.000 g Cd metal, acid cleaned with (1+9) HN03,
weighed accurately to at least four significant figures, in
50 mL (1+1) HN03 with heating to effect dissolution. Let
solution cool and dilute with reagent water in a 1-L
volumetric flask.
7.6.3 Chromium solution, stock, 1 mL = 1000 |jg Cr:
Dissolve 1.923 g Cr03 (Cr fraction = 0.5200), weighed
accurately to at least four significant figures, in 120 mL (1
+5) HN03. 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 |jg Cu: Dis-
solve 1.000 g Cu metal, acid cleaned with (1+9) HN03,
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Revision 1.0 September 1997
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weighed accurately to at least four significant figures, in
50.0 mL (1+1) HN03 with heating to effect dissolution. Let
solution cool and dilute in a 1-L volumetric flask with
reagent water.
7.6.5 Lead solution, stock, 1 mL = 1000 |jg Pb:
Dissolve 1.599 g Pb(N03)2 (Pb fraction = 0.6256),
weighed accurately to at least four significant figures, in a
minimum amount of (1+1) HN03. Add 20.0 mL (1+1)
HNO3 and dilute to volume in a 1-L volumetric flask with
reagent water.
7.6.6 Nickel solution, stock, 1 mL = 1000 |jg Ni:
Dissolve 1.000 g of nickel metal, weighed accurately to at
least four significant figures, in 20.0 mL hot concentrated
HNO3, cool, and dilute to volume in a 1 -L volumetric flask
with reagent water.
7.6.7 Selenium solution, stock, 1 mL = 1000 |jg Se:
Dissolve 1.405 g Se02 (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 sys-
tem. 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
the samples. The preparation blank must be carried
through the entire sample digestion and preparation
scheme.
7.8.3 The laboratory fortified blank (LFB) is prepared
by fortifying an aliquot of the laboratory reagent blank with
all analytes to provide a final concentration which will
produce an absorbance of approximately 0.1 for each
analyte. The LFB must be carried through the complete
procedure as used for the samples.
7.8.4 The rinse blank is a 0.1% HCI and 0.1% HN03
solution used to flush the autosampler tip and is stored in
the appropriate plastic containers.
7.9 Instrument Performance Check (IPC) Solution
The IPC solution is used to periodically verify instrument
performance during analysis. It should be prepared in the
same acid mixture as the calibration standards by com-
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 instru-
ment 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 absor-
bance 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.
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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 acid-
preserved, 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 collec-
tion.
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 neces-
sary 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 stan-
dards 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.8 To determine MDL
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:
200.12-9
Revision 1.0 September 1997
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MDL = (t) x (S)
where, t = Student's t value for a 99% confidence level
and a standard deviation estimate with n-1 degrees of
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-
cant change in the background or instrument response.
The MDLs reported in Table 2 were determined in forti-
fied 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 (Mand-
atory)
9.3.1 Laboratory reagent blank (LRB) The laboratory
must analyze at least one LRB (Section 7.8.2) with each
batch of 20 or fewer samples. LRB data are used to
assess contamination from the laboratory environment.
LRB values that exceed the MDL indicate laboratory or
reagent contamination should be suspected. Any deter-
mined source of contamination must be corrected and the
samples reanalyzed for the affected analytes after
acceptable LRB values have been obtained.
9.3.2 Laboratory fortified blank (LFB) The laboratory
must analyze at least one LFB (Section 7.8.3) with each
batch of samples. Calculate accuracy as percent recov-
ery (Section 9.4.3). If the recovery of any analyte falls
outside the required control limits of 85-115%, that
analyte is judged out of control, and the source of the
problem should be identified and resolved before
continuing analyses.
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 perfor-
mance 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.
9.3.4 Instrument performance check (IPC) solution -
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 con-
firms calibration to be 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 IPC solution must be reana-
lyzed. Data for the calibration blank and IPC solution
must be kept on file with associated sample data.
9.3.5 Matrix performance check (MPC) solution For
all determinations, the laboratory must analyze the MPC
solution (Section 7.11) immediately following daily cali-
bration, after every tenth sample (or more frequently, if
required) and after the last sample in the batch is ana-
lyzed. Analysis of the MPC must verify that the instrument
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200.12-10
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is within ± 15% of calibration and confirm that the matrix
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
data quality. Taking separate aliquots from the sample for
replicate and fortified analyses can in some cases assess
these effects. Unless otherwise specified by the data user,
laboratory or program, the following laboratory fortified
matrix (LFM) procedure (Section 9.4.2) is required. Also,
the analyte addition test (Section 9.5.1) can aid in
identifying matrix interferences. However, all samples
must have a background absorbance < 1.0 before the
test results obtained can be considered reliable.
9.4.2 The laboratory must add a known amount of
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
9.4.4 If the recovery of any analyte falls outside the
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
recovery of the LFM should be calculated. If the fortified
analyte in the diluted LFM is found to be < 25% of the
sample concentration or the diluted LFM produces an
atomic signal of <10 times the MDL, the diluted sample
should be analyzed by methods of standard addition. If
the calculated recovery of the diluted sample is within the
designated range, the sample concentration should be
calculated from the diluted sample. If the calculated
recovery of the diluted sample is outside the designated
range, follow the directions given below. If the back-
ground is reduced and/or the matrix effect is reduced by
dilution, all samples of a similar matrix should be diluted
and analyzed in a similar fashion. The result should be
flagged indicating the methods sensitivity has been re-
duced 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.
where, R = percent recovery.
Cs = fortified sample concentration.
C = sample background concentration,
s = concentration equivalent of analyte
added to sample.
200.12-11
Revision 1.0 September 1997
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3. If the recovery of the analyte addition test is less
than recovery calculated for the LFM, matrix sup-
pression is confirmed. The unfortified sample
should be analyzed by MSA (Section 11.3).
Significantly lower recoveries (relative to the LFM)
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 homoge-
neous.
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 con-
tamination of the LFM, an incorrect analyte concen-
tration 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 inter-
ference is suspected. This dramatic change in re-
sponse 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 differ-
ence 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
prevents successful determination of the analyte or when
the heterogeneous nature of the sample precludes the
use of duplicate analyses.
9.4.6 Where reference materials are available, they
should be analyzed to provide additional performance
data. Analysis of reference samples is a valuable tool for
demonstrating the ability to perform the method accept-
ably. 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 spectropho-
tometers 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 manufac-
turer 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 100°C below the point at which analyte begins
to be lost during the char. Because the background
absorbance can be affected by the atomization tempera-
ture, care should be taken in the choice of an appropriate
atomization temperature. The optimum conditions se-
Revision 1.0 September 1997
200.12-12
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lected should provide the lowest reliable MDLs and be
similar to those listed in Table 2. Once the optimum
operating conditions are determined, they should be
recorded and available for daily reference. The effective-
ness of these operating conditions are continually evalu-
ated 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 cath-
ode 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 ana-
lyze 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 Re-
coverable 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 85°C. (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 85°C. (Once the beaker is covered
with a watch glass the temperature of the water will rise
to approximately 95°C.)
11.1.2 Reduce the volume of the sample aliquot to
about 20 mL by gentle heating at 85°C. 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.)
11.1.3 Cover the lip of the beaker with a watch glass to
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 over-
night, 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, in-
spect 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 HzO (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. Ini-
tiate 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
200.12-13
Revision 1.0 September 1997
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relative standard deviation is > 5%, determine and correct
the cause before calibrating the instrument.
11.2.5 For initial and daily operation, calibrate the in-
strument according to the instrument manufacturer's
recommended procedures using the calibration blank
(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 sys-
tem 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,
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.
11.2.11 When it is necessary to assess an operative
matrix interference (e.g., signal reduction due to high
dissolved solids), the test described in Section 9.5 is
recommended.
11.2.12 Report data as directed in Section 12.
11.3 Standard Additions - If the method of standard
addition is required, the following procedure is recom-
mended:
11.3.1 The standard addition technique9 involves pre-
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 Vx, are taken. To the first
(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:
Q Sg VSCS
X~(SA-SB)VX
where, SA and SB are the analytical signals (corrected
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 re-
spond in the same manner as the analyte in the
sample.
3. The interference effect must be constant over the
working range of concern.
Revision 1.0 September 1997
200.12-14
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4. The signal must be corrected for any additive inter-
ference.
12.0 Data Analysis and Calculations
12.1 Sample data should be reported in units of //g/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 /ig/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
additional dilutions required to complete the analysis.
12.3 The QC data obtained during the analyses
provide an indication of the quality of the sample data and
should be provided with the sample results.
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 ob-
tained 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
EPA has established a preferred hierarchy of environ-
mental management techniques that places pollution
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 institu-
tions, consult Less is Better: Laboratory Chemical Man-
agement for Waste Reduction, available from the Ameri-
can 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
15.1 The Environmental Protection Agency requires
that laboratory waste management practices be con-
ducted consistent with all applicable rules and regula-
tions. The Agency urges laboratories to protect the air,
water, and land by minimizing and controlling all releases
from hoods and bench operations, complying with the
letter and spirit of any sewer discharge permits and
regulations, and by complying with all solid and hazard-
ous 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).
200.12-15
Revision 1.0 September 1997
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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.
Revision 1.0 September 1997
200.12-16
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17.0 Tables, Diagrams, Flowcharts, and Validation Data
Table 1. Furnace Conditions for Determination of Metals in Seawater1
Element
Wavelenath Cnml
Slit Width (nm)
Method of
Analysis
Modifier23
Furnaces5
Cycle
Temp
°C
Temp
Ramp
Hold Time (sec)
As
193.7
Direct
Pd/Mg
Dry
130
1
60
0.7
Char
14004
10
60
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 ,ug
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
14004
10
30
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% HN03 on
Char
1000
5
60
or
Platform
Atomization
2100
0
5
Std. Addition
1 10-^iL sample size.
2 5|iL of (30 mg Pd Powder and 20 mg Mg(N03)2-6H20 to 10 mL).
3 A gas mixture of 5% H2 in 95% Ar is used during the dry and char.
4 Sodium emission is visibly exiting from the sample inlet port.
5 The furnace program has a cool down step of 20° between char and atomization and a clean out step of 2600° C after atomization.
Table 2. MDLs and Background Absorbances Associated with a Fortified NASS-31"3
Typical
Integrated
MDL5
Background
Element
//g/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
Se4
9.5
1.4
As4
2.6
0.3
1 Matrix Modifier = 0.015 mg Pd + 0.01 mg Mg(N03)2.
2 A 5% H2 in Ar gas mix is used during the dry and char steps at 300 mL/min for all elements.
3 10-//L sample size.
4 An electrodeless discharge lamp was used for this element.
5 MDL calculated based on fortifying NASS-3 with metal analytes.
6 Background absorbances are affected by the atomization temperature for analysis, therefore, lowering atomization temperatures may be
advantageous if large backgrounds are observed.
- Not Determined.
200.12-17
Revision 1.0 September 1997
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Table 3. Precision and Recovery Data for Fortified NASS-3
Element
Certified
Value
Observed
Value
Fortified
Cone.
Avg.
Fortified
Cone.
%RSD
Avg.
% RSD
As
1.65 ± 0.19
< MDL
15
89
3.6
37.5
85
1.6
Cd1
0.029 ± 0.004
< MDL
1.0
107
4.5
2.5
104
3.8
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
Se1
0.024 ± 0.004
< MDL
25
101
2.9
62.5
99
3.9
Standards were made in 10,000 ppm NaCI for this analysis.
Determined from four sample replicates.
ai
0
c
CO
_Q
1
o
to
_Q
<
"O
c
3
e
O)
o
<0
CD
ŠO
-------
3.221 -i
Current Atomic
Current Backgrd
H
Š *
F
Time (sec)
5.00
Figure 2. Pb atomization Profile Utilizing a 800° Char.
Microliters of Fortified NASS-3
Figure 3. Normalized Integrated Absorbance vs. Microliters of Fortified NASS-3.
All Samples Fortified with 5 ul of Standard
200.12-19
Revision 1.0 September 1997
-------
as
a>
15
110
105
100
95
90
85
5 jul of a Cd Standard Added
+NASS-3
NaC110,000 ppm
80
75
70
Microliters of Matrix
Figure 4. Cd Response in NASS-3 and 10,000 ppm NaCI.
_o
<
73
CD
H
Ol
110
100
90
80
70
5 jul of Se Standard Added
+ Seawater
60
50
J.
-L
J.
4 6
Microliters of Matrix
10
Figure 5. Se Response in Seawater vs 10,000 ppm NaCI
Revision 1.0 September 1997
200.12-20
-------
(1) Poor Transfer
(2) Sample Heterogeneity
(3) Digestion/Precipitation
(4) Matrix Suppression/Enhancements 'FA = In Furnace Analyte Addition
(5) Contamination
Report Results on Diluted Sample
Report Results on
85% < IFA <
I FA = LFM
IFAs > LFM Compare
Recoveries
T) 4 IFAs to LFM IFA > 115
No
MSA <
~ MSA
% Recovery
Yes
Yes
MSA
Yes
No
No
Yes
No
IFAs < LFM Compare
Recoveries
IFAs to LFM
IFA < 85
MSA -4
^ MSA
Background
Absorbance
< 1.0 abs
Yes
IFAs > 85%
Fortified
Cone
< 10MDL
or
< 25% Sample
Cone
Background
Absorbance
<1.0 abs
Dilute 1:3
Sample & LFM
Calculate %
Recovery
Reanalyze
IFA Analysis
on
Sample
See 9.5
LFM >125%
LFM < 75%
IFA Analysis
on
Sample
See 9.5
Suspected Matrix
Interference
Recovery
75% > LFM > 125%
Start
1 ) ( 2 ) ( 3 ,
Report Results on Unfortified Sample
Figure 6. Matrix Interference Flowchart.
200.12-21
Revision 1.0 September 1997
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