INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION
ANALYSIS OF DRINKING WATER
APPENDIX TO METHOD 200.7
REVISION 1.3
"Inductively Coupled Plasma Atomic Emission Spectrometric
Method for Trace Element Analysis of Water and Wastes"
Theodore D. Martin, Eleanor R. Martin
and Gerald D. McKee
Physical and Chemical Methods Branch
Environmental Monitoring and Support Laboratory
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
CINCINNATI, OHIO 45268
MARCH 1987

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i" Scope and Application
1.1	This procedure is designed to be a supplement to Method 200 7 (1)
and 1s to be used in processing drinking water supply samples prior
to inductively coupled plasma-atomic emission spectrometric
(ICP-AES) analysis. This appendix does not supercede Method 200 7
u!LPIi0oides e1aboration on the analysis of drinking water using" *
Method 200.7. For a listing of the recommended wavelengths,
Definitions, and discussions on Safety, Reagents and Standards, and
sample Handling and Preservation see the appropriate Sections of
Method 200.7.
1.2	This procedure is to be used for the total element determination of
primary and secondary elemental drinking water contaminants
included in Method 200.7. It is only to be used for compliance
monitoring when the determined method detection limit (MDL) (2) for
a particular contaminant is no greater than 1/5 its respective
maximum contaminant level (MCI) concentration. For these reasons,
mercury and selenium have been omitted from this edition of the
appendix. A listing of the contaminants for which the procedure is
applicable along w.ith their MCls and MDls is given as Table 1.
1.3	This procedure is to be used in all pneumatic nebulization ICP
analyses for compliance monitoring of drinking water, and is
recommended for the analysis of ground and surface water where
determination at the drinking water MCI is requested.
1.4	This procedure also can be used to determine the concentration of
calcium (Ca) for calculating corrosivity and for the required
monitoring of sodium (Na). Since these two elements can occur in
waters at concentrations greater than 25 mg/l, particular care must
be taken that concentrating the sample does not cause the analysis
^wo dements to exceed the calibration limit of
linearity. If standardization of the instrument does not include
provision for non-linear calibration, a more convenient and
allowable determination of these two elements is the direct
aspiration analysis of the acidified unprocessed sample.
2. Summary of Method
2.1	For a description of the analytical technique and method summary
see Section 2 of Method 200.7.
2.2	Analytical Oiscussion
2.2.1 The analysis of drinking water for elemental contaminants
requires that a "total" element determination be made.
Irrespective of the valence state or chemical species, the
term "total" refers to the sum of the elemental
concentration in the dissolved and suspended fractions of
the sample. The sample is not filtered, but irnnediately
preserved with nitric acid to pH of less than 2 at the time
of collection.
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2.2.2	Although most finished drinking waters are free of suspended
matter, all samples must be subjected to a pretreatment acid
dissolution to solubilize that portion of the-contaminant
that may be occluded or adhering to minute suspended
matter. This is especially true for water supplies that
receive only chlorination pretreatment. Once solubilized,
the energy of the plasma is sufficient that all species in
the nebulized droplets are desolvated, dissociated and
raised to an energetic excited state for atomic emission
spectrometric analysis.
2.2.3	Method 200.7 describes two acceptable sample preparation
procedures for "total" element analyses. One is a vigorous
nitric acid digestion (Section 9.3), while the other is a
total recoverable acid solubilization procedure (Section
9.4). These procedures *re essentially the same as those
used for flame atomic absorption analysis, except the final
acid concentration has been changed to match the ICF
calibration standards. The total recoverable procedure is
preferred for drinking water analyses because there is less
chance of losses from volatilization, the formation of
insoluble oxides or occlusion in precipitated silicates.
2.2.4	Data that are to be used for compliance monitoring should be
reported with a known estimate of uncertainty. The
uncertainty of the analysis should be determined at the
critical MCI concentration and should be a precision of
small enough variance to determine that the contaminant is
either in-or-out of compliance. A quide for evaluating data
to be reported can be described as data with sufficient
precision at the MCI, that when two standard deviations are
either added to or subtracted from the MCL concentration,
the value is not changed by more than 101. An example is As
(MCL - 0.05 mg/L) where data reported with a precision of
two standard deviations equal to less than 0.005 mg/L would
be acceptable as shown in the preconcentration data of
Table 2 with the interval values of 0.048 to 0.052 mg/L.
2.2.5	As indicated in Table 1, the MCLs for As and Pb are close to
their estimated instrumental detection limits. A single
analysis of these two elements using the total recoverable
procedure 9.4 of Method 200.7 lacks the precision needed for
compliance monitoring at their respective MCls. As a
consequence inaccurate determinations can result. Only with
repeated analyses of the sample can an average value with
acceptable precision be determined. The number of analyses
required can be specified by the following equation:
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¦ • If
where: n - the number of replicate analyses required,
Sa - the determined standard deviation of a single
observation, and
Sx - the standard deviation deemed acceptable around
the mean value for n detenninations.
Using the preceding equation the number of repeated analyses
required for the procedure 9.4 can be calculated from the
direct analysis standard deviation data given in Table 2.
For each element the listed determined standard deviation is
Sa and the acceptable standard deviation is Sx. From the
calculation the number (n) of repeated analyses required for
As is 8, while for Pb the number is 6. (Note: From the
standard deviation data listed for analysis after 4X
concentration, the number for both elements is 1.)
2.2.6 The drinking water procedure that follows (5.1) is a
modification of the total recoverable procedure 9.4 Method
200.7 that provides for improved precision and accuracy by
concentrating the contaminants 4X prior to ICP analysis.
With preconcentration the determination is made on a more
reliable portion of the calibration curve. Also, since the
variability over the narrow concentration range in question
is nearly constant and does not.change significantly by
concentrating the sample 4X, the precision of the
determination improves when the concentrated value is
divided by 4 to calculate the analyte concentration in the
original sample. Table 2 gives a comparison of precision
and accuracy for the two elements As and Pb as determined by
direct analysis and after preconcentration. The data for
the direct analysis were determined from seven replicate
analyses of a single unconcentrated aliquot while the
preconcentration data were determined from the analysis of
seven aliquots after preparation using the procedure
described in 5.1. The percent recovery range data are the
spread of the average percent recoveries from the seven
replicate analyses determined on four separate days. The
mean value is the average of the spread. The listed
standard deviation is from the set of replicate analyses
having the greatest variance.
3. INTERFERENCES
3.1 Concentration of surface, ground and drinking water supply samples
can produce slight spectral and matrix interferences in ICP
analysis. Reported effects have not been severe with the spectral
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interference being an elevated shift in background intensity, while
the matrix interference causes the signal intensity of some
analytes to be reduced. In both cases the alkaline earth elements,
calcium (Ca) and magnesium (Mg), are the primary interferents. For
a complete description of interferences affecting ICP analysis see
Section 5 of Method 200.7.
Spectral Interference
3.2.1 The technique of "off-the-line background correction
adjacent to the wavelength peak," as required in Method
200.7, is usually adequate to compensate for shifts in
background intensity. To test the spectral location
selected for background correction, analyze analytically
pure, single element Ca and Mg solutions of high
concentration {>500 mg/L) and compare the data to the
instrumental detection limit from acid blank
determinations. If a value falls outside a confidence
interval of *2 standard deviations around the Instrumental
detection limit, the wavelength should be spectrally scanned
for selection of a different background location. If it is
not feasible to change the background correction location,
an interelement correction factor can sometimes be used. An
example is the effect of Ca on the recotrtnended wavelength
for Pb (220.353 nm). A non-uniform background shift occurs
on the low side of the wavelength peak; however, the
location is not changed because of a possible severe
spectral interference from A1 on the high side of the
wavelength peak. For the situation described only a very
small, correction factor (-0.00002) is required for the
EMSL-Cincinnati instrument. When using interelement
correction for this purpose, the correction should not be
completed when the determined interferent concentration
deviates from linearity by more than 10% or unless the
equation used in standardization includes terms for
non-linear calibration.
3.2.2 Although no significant interelement spectral line
interferences have been reported from the alkali and
alkaline-earth elements on the wavelengths specified for the
contaminants listed in Table 1, the EMSL-Cincinnati
instrument does experience a weak Mg interference at
0.037 nm below the recommended Zn wavelength (213.856 nm)
read in the second order. To avoid a possible Mg spectral
interference, background intensity should be read on the
high side of the Zn wavelength peak. Another possible
spectral interferent whose effect should be determined is
that of A1 on the recommended wavelengths for As, Mn and
Pb. Also, care must be taken that spectrally interfering
elements are not mixed in the same calibration standard
unless the computer program provides for their correction
during standardization".

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3.3 Matrix Interference
3.3.1	As the dissolved solids in the solution to be nebulized
increase to exceed a concentration of 1500 mg/l, a
suppressive effect on the analyte signal can occur. The
most noticeable effect has been observed on certain analytes
where a characteristic ion line is the preferred wavelength
for the analysis. To determine the presence of a
suppressive interference because of concentrating the
matrix, a second aliquot of the sample should be spiked with
each element to a concentration above 10X its determined MDL
(but not to exceed its MCI), concentrated and analyzed.
Recoveries outside the interval of 90% to 110% of the
expected value can be used to indicate the presence of a
matrix interference.
3.3.2	At EMSL-Cincinnati, using a fixed crossflow nebulizer with
the instrument conditions given in Section 4.2, it has been
observed that high concentrations of Ca (>400 mg/l) can
cause a 5% suppressive effect on the emision signal of
certain analytes; Cd and Pb experience the greatest,
suppression. As the concentration of Ca increases, its
suppressive effect becomes more pronounced. AT so, Mg has an
additive suppressive effect on Pb, and this combined effect
must be recognized when considering matrix interferences.
3.3.3	When the concentration of a primary contaminant is
determined to be 90% of its MCI or above, and the Ca
concentration exceeds 400 mg/l (100 mg/L in the original
sample concentrated 4X) or the combined Mg and Ca
concentration equals 500 mg/L, a matrix matched calibration
standard must be used. Otherwise the sample should be
analyzed by the standard addition technique (see Section
10.6 of Method 200.7).
4. APPARATUS
4.1	In addition to the minimum requirements listed in Section 6 of
Method 200.7, the use of mass flow controllers to regulate the
argon flow rates, especially through the nebulizer, provide more
exacting control and reproducible plasma conditions. Their use is
highly recommended, but not required.
4.2	Operating conditions — Because of differences between various
makes and models of satisfactory instruments, no detailed operating
instructions can be provided. However, the following instrument
conditions were used in conjunction with a fixed crossflow
nebulizer in developing the analytical data contained in this
appendix:
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Operating Conditions
Forward rf power
Reflected rf power
Viewing height above
1100 watts
< 5 watts
work coil
Argon supply	L
Argon pressure
Coolant argon flow rate
Aerosol carrier argon
16
Liquid
mm
Argon
40
19
flow rate
Auxilliary (plasma)
630 cc min-1
argon flow rate
Sample uptake rate
300 cc min~l
controlled to
1.2 mL nrin-1
5.	SAMPLE PREPARATION
5.1 Transfer a 200 mL aliquot of a well mixed acid preserved sample to
a Griffin beaker. Add 1.0 mL of (1+1) HNO3 and 5.0 ml. (1+1) HCL
to the sample and heat on a steam bath or hot plate until the
volume has been reduced to near 20 mL making certain the sample
does not boil. Allow the sample to cool, transfer to a 50 mL
volumetric flask, dilute to the mark with deionized-distilled water
and mix. The sample is now ready for analysis. If after
preparation the sample contains particulate matter, an aliquot
should be centrifuged or the sample allowed to settle by gravity
before aspiration.
6.	QUALITY CONTROL
6.1 Instrumental
6.1.1	For required instrumental quality control see Section 12 of
Method 200.7.
6.1.2	(Optional) To monitor nebulizer performance and aerosol
effects in the plasma, a surrogate spike of a noncontaminant
element (Au) is added at a concentration of 2 mg/L (1 mL of
100 mg/L Au per 50 mL sample) to each sample after
dissolution, but before final dilution. If the analyzed Au
value is not within *5% of the true value, either the
nebulizer or torch has become partially clogged or a
suppressive matrix effect has occurred. An analysis of the
instrument check standard will indicate if shutdown and
cleaning is required. (Note: EMSL-Cincinnati has been able
to use the "high surge" argon flow when the mass flow
controller is first opened, to flush clean the argon port of
the nebulizer. This purging is usually done during the
print-out of analytical data and has proven in almost all
instances to restore calibration drift back to its original
calibration.)
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6.2 Method Detection Limit (Mandatory)
6.2.1 The MDL (2) must be determined for each contaminant using
the described procedure in 5.1 with the instrument system
configured in mode to be used for compliance monitoring.
The determined MDL concentration must be no greater than 1/5
the element's respective MCL before the procedure and
instrument system can be used for compliance monitoring of
that particular contaminant. The MOL must be redetermined
once a year and all data must be maintained on file.
6.3 Method (Mandatory)
6.3.1	The following method quality assurance represents 15% of the
analyzed sample Toad for 20 samples.
6.3.2	A reagent blank as defined and described in 3.12 and 7.5.2
of Method 200.7 should be processed through the entire
procedure with each group of samples. The analyzed value
for each contaminant should be less than its determined
MDL. If the analyzed value is greater than the MDL, con-
tamination is suspected and succeeding analyses should be
closely monitored for systematic errors. If the analyzed
value exceeds the reporting limit, the analysis is consi-
dered to be out of control. The source of contamintion
should be determined, corrected and the samples reanalyzed.
6.3.3	To measure the precision of the analysis, one sample of
every 20 is selected at random, spiked in duplicate and
analyzed. The two aliquots are spiked with all 10
contaminants and processed through the entire procedure.
The resulting spike concentration of each contaminant should
be above 10X its determined MOL but not to exceed its MCL.
The relative difference (RD) between the spiked duplicates
for each contaminant is then compared to a previously
established critical relative difference (CRD) determined
from 15 prior spiked duplicate sample analyses of the same
concentration. If the RD exceeds the CRD, the analysis is
considered to be out of control. The RD between the spiked
duplicates is determined by dividing their difference in
concentration by their mean concentration. The CRD can be
calculated using the following equation:
CRD - 3.27
n
i-1
Ri
li
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where: Ri - is the calculated difference between the
spiked duplicates in each set,
Xi « is the mean value of the spiked duplicate set
and
n « is the number (15) of spiked duplicate sets
analyzed
6.3.4 To measure the accuracy of the analysis, percent recovery of
the spike is determined. The analysis of the unspiked
sample aliquot is subtracted from the mean concentration of
the analyzed spiked duplicates. If the sample concentration
is less than the spike concentration, and the percent
recovery of the spike is outside an interval of 90% to 110%
of the expected value, the analysis is considered to be out
of control. If the spike recovery is acceptable, the
determination is an indication of accuracy for the matrix
spiked. Only, if all samples analyzed have a similar
matrix, can the spike recovery be an indication of accuracy
for all samples.
7.	Procedure
7.1	See Section 10 of Method 200.7 for the recommended and required
analytical operating procedures.
7.2	To eliminate possible memory carry-over from sample to sample, a
washout time of at least 30 sec. between succeeding aspirations
should be strictly observed.
7.3	To assure that the sample has reached equilibirum in the plasma,
the sample should be aspirated for 15 sec. after reaching the
plasma before beginning the integration of the background corrected
emission signal.
7.4	The data provided in support of this appendix were determined using
an average value of four, 4 sec. background corrected integration
periods.
8.	Calculations
8.1	All determined concentrations should be divided by four prior to
reporting data.
8.2	Reagent blank concentrations less than the upper control limit of
the MDL (UCl - 2.2 x MDl) should not be subtracted from the samples.
8.3	All data should be rounded to the thousandth place and reported in
mg/L up to three significant figures.
8.4	Sample concentrations less than the upper control limit of the MOL
should be reported as "not detected". Data reported in this manner
will have a confidence level of 95% certainty that false positives
are not reported. (See footnote 2 of Table 1.)
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9.	Precision and Accuracy (Single laboratory, EMSL-Cincinnati)
9.1	Table 3 lists precision and accuracy data for seven aliquots of
deionized distilled water spiked with each contaminant at a
concentration near its reporting limit, concentrated 4X by the
described procedure, and analyzed using a simultaneous ICP
instrument.
9.2	Table 4 lists precision and accuracy data for verification of ICP
analysis of drinking water. Seven aliquots of Cincinnati, Ohio tap
water were spiked with each contaminant at its respective MCL,
prepared by the described procedure, and analyzed using a
simultaneous ICP instrument. Table 4 lists the spike value, the
mean and percent recovery of spike after tap water blank
subtraction, the standard deviation and the 95% confidence interval
about the respective MCL.
9.3	Precision and accuracy data for seven aliquots of Cincinnati, Ohio
tap water spiked to a concentration of 1/2 the MCL are listed in
Table 5.
9.4	Table 6 lists the mean, standard deviation and percent recovery of
a spike of each contaminant added to 12 separate ground water
drinking supplies having concentrations of Ca and Mg ranging from
14 to 82 mg/L and from 0.7 to 20 mg/L, respectively. The spike
concentration selected for each contaminant was a convenient value
between its MCL and 10X its determined MDL. Any naturally
occurring background levels subtracted were the average value of
duplicate analyses of the unspiked sample.
10.	References
1.	Method 200.7 - Inductively Coupled Plasma-Atomic Emission
Spectrometric Method for Trace Element Analysis of Water and
Wastes, EPA-600/4-79-020, revised 1984, U.S. Environmental
Protection Agency, Environmental Monitoring and Support Laboratory,
Cincinnati, Ohio 45268.
2.-	Glaser, J., Foerst, D., McKee, G., Quave, S., and Budde, W., "Trace
Analyses for Wastewaters," Environmental Science and Technology,
Vol. 15, No. 12, December 1981, pp 1426-1435.
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TABLE 1.
COMPARISON OF ICP
DETECTION
LIMITS, MG/L

Maximum
Estimated
Method Detection Limit
EMSL-Cinf
Contaminant
Detection
Procedure
Modified 4X
Reporting
Element
Level
Limit (1)
9.4
Procedure
Limit(2)
Primary





Silver (Ag)
0.05
0.007
0.0028
0.0013
0.004
Arsenic (As)
0.05
0.053
0.0157
0.0030
0.008
Barium (Ba)(3)
1
0.002
0.0013
0.0004
0.002
Cadmium (Cd)
0.010
0.003
0.0013
0.0006
0.002
Chromium (Cr)(3)
0.05
0.006
0.0031
0.0006
0.002
Lead (Pb)
0.05
0.042
0.0157
0.0046
0.011
Secondary





Copper (Cu)
1
0.005
0.0028
0.0007
0.002
Iron (Fe)
0.3
0.006
0.0063
0.0037
0.009
Manganese (Mn)
0.05
0.002
0.0003
0.0002
0.001
Zinc (Zn)(3)
5
0.002
0.0019
0.0010
0.003
(1)	The estimated instrumental detection limits as shown are taken from "Inductively
Coupled Plasma - Atomic Emission Spectroscopy - Prominent Lines,"
EPA-600/4-79-017.
(2)	Method 200.7 states "data should be rounded to the thousandth place and all
results should be reported in mg/L up to three significant figures." The listed
reporting limit for each element is an adjusted 95% upper control limit (UCL) of
the corresponding 4X method detection limit. The reporting limit takes into
account rounding errors and prevents false positive values below the upper
control limit from inadvertently being reported (UCL - 2.2 X MDL).
(3)	The EMSL-Cincinnati instrument uses wavelengths for Ba (493.409 nm) and Cr
(205.552 nm read in the 2nd order) that are different from those recommended in
Method 200.7. Also, the Zn wavelength (213.856 nm) is read in the 2nd order.
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Element
As
Pb
MCL
Spike
0.05
0.05
TABLE 2. COMPARISON OF PRECISION AND ACCURACY
CONCENTRATION, MG/L
Direct Analysis, Not Concentrated
Determined Precision
Percent Recovery
Range Mean
84 - 108%
88 - 106*
99%
100%
Standard
Deviation
* 0.007
± 0.006
95% Confidence
Interval at MCL
0.036 - 0.064
0.038 - 0.062
Acceptable Precision
Standard * 10% Interval
Deviation About the MCL
± 0.0025
± 0.0025
0.045 - 0.055
0.045 - 0.055
As
Pb
Preconcentrated 4X Before Analysis
0.05	98 - 102% 101% * 0.001	0.048 - 0.052 ± 0.0025
t
0.05	96 - 102% 99% * 0.002	0.046 - 0.054 ± 0.0025
0.045 - 0.055
0.045 - 0.055
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TABLE 3. PRECISION AND ACCURACY DATA IN DEIONIZED DISTILLED WATER
FOR CONCENTRATIONS NEAR THE REPORTING LIMIT, MG/L

Reporting
Spike

Standard
Percent
Element
Limit
Cone.
Mean (1)
Deviation
Recovery
Ag
0.004
0.0020
0.0021
* 0.0002
105*
As
0.008
0.0100
0.0107
* 0.0012
107*
Ba
0.002
0.0025
0.0028
* 0.0002
108*
Cd
0.002
0.0025
0.0024
* 0.0002
96*
Cr
0.002
0.0025
0.0027
* 0.0002
108*
Cu
0.002
0.0020
0.0018
± 0.0002
90*
Fe
0.009
0.0160
0.0170
* 0.0006
107*
Mn
0.001
0.0025
0.0025
± 0.0001
100*
Pb
0.011
0.0100
0.0097
* 0.0013
97*
Zn
0.003
0.0040
0.0044
* 0.0006
110*
(1) The reported data are listed to the ten-thousandths place to correspond
to the spike level used.
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TABLE 4. DRINKING WATER PRECISION AND ACCURACY DATA CINCINNATI, OHIO TAP WATER
CONCENTRATION, MG/L
MCL	Average Recovery Standard 95% Confidence
Element Spike Mean (1) Percent Deviation Interval at MCL
Ag
0.05
0.0497
99%
±
0.001
0.048
-
0.052
As
0.05
0.0503
101*
*
0.001
0.048
-
0.052
Ba
1
0.978
98%
±
0.025
0.950
-
1.050
Cd
0.010
0.0097
97%

0.0002
0.0096
-
0.0104
Cr
0.05
0.0479
96%
±
0.001
0.048
-
0.052
Cu
1
1.01
101%
±
0.024
0.952
-
1.048
Fe
0.3
0.291
97%
±
0.006
0.288
-
0.312
Mn
0.05
0.0507
101%

0.001
0.048
-
0.052
Pb
0.05
0.0497
99%
±
0.002
0.046
-
0.054
Zn (2)
1
0.989
99%
±
0.019
0.962
-
1.038
(1)	The mean concentrations listed to the ten-thousandth's	place are
recorded data before rounding. The data are presented	in this manner to
coincide with the reported percent recovery.
(2)	The data listed for Zn are for a concentration 1/5 the MCL.
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TABLE 5.	DRINKING WATER	PRECISION AND ACCURACY DATA CINCINNATI, OHIO TAP WATER
CONCENTRATION, MG/L
Spike Cone.	Standard	Percent
Element	1/2 MCL	Mean (1)	Deviation	Recovery
Ag	0.025	0.0245	* 0.0004	98*
As	0.025	0.025	* 0.001	100*
Ba	0.500	0.490	* 0.010	98*
Cd	0.005	0.005	* 0.0001	100*
Cr	0.025	0.024	± 0.0003	96*
Cu	0.500	0.494	± 0.008	99*
Fe	0.150	0.147	± 0.002	98*
Mn	0.025	0.0245	* 0.0003	98*
Pb	0.025	0.025	* 0.001	100*
Zn(2)	0.500	0.495	* 0.004	99*
(1)	The mean concentrations listed to the ten-thousandth's place are
recorded data.before rounding. The data are presented in this manner to
coincide with the reported percent recovery.
(2)	The data listed for Zn are for a concentration 1/10 the MCL.
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