United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV 89193
Research and Development
EPA/600/S4-87/032 Jan. 1988
AEPA Project Summary
An Interlaboratory Study of
Inductively Coupled Plasma
Atomic Emission Spectroscopy
Method 6010 and Digestion
Method 3050
Clifton L. Jones, Vernon F. Hodge, Donald M. Schoengold,
Homigol Biesiada, Thomas H. Starks, and Joseph E. Campana
The design, execution, and results of
an interlaboratory study of Method
6010, "Inductively Coupled Plasma
Atomic Emission Spectroscopy," are
described. This study examined the
application of the method to the anal-
ysis of solid-waste materials for 23
elements. Part of the interlaboratory
study included a study of Method
3050, ' 'Acid Digestion of Sediments,
Sludges and Soils," which is integral
to Method 6010 when considering the
analysis of certain solid wastes. The
overall study was designed so that the
variability of the two methods was
separable. Method performance data,
including precision and accuracy, are
presented and discussed. A compari-
son of the inductively coupled plasma
atomic emission and atomic absorption
spectroscopic techniques is presented,
as well as a comparison of results from
two different types of inductively
coupled plasma spectrometers. The
limitations of the methods are des-
cribed, and suggestions are given to
improve the general application of
Method 6010.
This Project Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems Laboratory, Las Vegas,
NV, to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
An interlaboratory study of solid
wastes using the EPA analytical Method
6010 entitled "Inductively Coupled
Plasma Atomic Emission Spectroscopy"
(ICP-AES), which is included in the EPA
methods publication SW-846, was
performed with nine participating labor-
atories. This interlaboratory study con-
centrated on the application of Method
6010 for the determination of 23 ele-
ments in seven solid materials including
dried sludges, sediments, and fly ash.
The 23 target elements are: Al, Sb, As,
Ba, Be, Cd, Ca, Cr, Co, Cu, Fe, K, Pb, Mg,
Mn, Mo, Ni, Se, Ag, Na, Tl, V. and Zn.
This study followed a single-laboratory
evaluation that investigated the applica-
tion of Method 6010 to a variety of
aqueous and solid-waste samples. The
different waste matrices studied in the
single-laboratory evaluation required the
utilization of several different digestion
procedures. In contrast, this interlabora-
tory study examined Method 6010 for the
analysis of solid wastes that were
digested using a single digestion
procedure.
Since the digestion of solid samples
is necessary to apply Method 6010 for
the analysis of wastes, a thorough study
of Method 6010 must also include
digestion as a variable. Consequently, a
parallel study of Method 3050 (Acid
Digestion of Sediments, Sludges, and
Soils) was included as an integral part
-------
of the interlaboratory study. The present
study was designed to determine the
performance of Method 6010 both
independent of and together with the
Method 3050 digestion procedure.
Seven solid materials, representative
of solid wastes, were selected as the
method evaluation materials. Three of
the materials (river sediment, coal fly
ash, and estuarine sediment) are Stand-
ard Reference Materials from the
National Bureau of Standards, and one
material (the mine tailing) is an EPA
reference material. The other three solids
(a contaminated soil and two industrial
sludges) were obtained from the EPA. A
detailed homogeneity study was per-
formed by the coordinating laboratory
before the solids were distributed to the
participating laboratories. The results
indicated that the solid samples were
homogeneous.
Sixteen grams of these homogeneous
solids were distributed to the laboratories
to be digested by Method 3050, both
unspiked and spiked. The spiking solu-
tions provided to the laboratories con-
tained 19 of the 23 target elements. They
were designed to be added to the solids
prior to digestion to bring the concen-
trations of the 19 elements in the
laboratories' digests to minimum levels
of about 100 times the corresponding
"Estimated Instrumental Detection Lim-
its" given in Method 6010. It was not
necessary to spike Al, Ca, Fe, and Mg
into the solids because of the high
endogeneous concentrations of these
metals in the 7 solid samples. Having
each laboratory spike portions of the solid
samples with the spiking solutions prior
to digestion assured that each laboratory
used equally spiked aliquots of the solids.
This procedure eliminated the need to
create uniformly spiked solids for distri-
bution. The resulting digests were
analyzed by Method 6010.
In order to remove sample-preparation
variability from measurement variability,
bulk digests of the 7 solid samples were
prepared by the coordinating laboratory
for distribution to the participating
laboratories. These bulk digests were
spiked with the same spiking solutions
that were used to spike the solid samples.
Thus, the spiked bulk digests of the seven
solid samples were very similar in
composition to the spiked solids digests
that were prepared by the laboratories.
Therefore, data from the Method 6010
analyses of these spiked bulk digests
could be compared to data from the
spiked solids in order to estimate the
variances due to the digestion and
analysis procedures. In order to test the
effects of high levels of V and Mo on the
determination of the other analytes by
Method 6010, the spiked bulk digest from
the fly ash solid was also spiked to
contain 0.1 percent of these interfering
elements.
In addition to the solid samples and
the spiked bulk digests, two QC solutions
containing the target elements were
provided to the participating laboratories
for analysis with and without digestion.
Because these solutions were carefully
prepared and verified by the coordinating
laboratory, the results could be used to
estimate the accuracy of the Methods.
Other solutions were provided to the
participating laboratories to insure high
ICP-AES data quality. These were initial
calibration verification solutions and an
interference check solution.
The results of this collaborative study
yielded quantitative information on the
precision and accuracy of Method 6010,
independently and together with Method
3050. Data obtained on sequential and
simultaneous ICP-AES instruments as
well as by atomic absorption spectros-
copy (AAS) were compared statistically,
and the results are reported. The method
of standard additions (MSA) is a condi-
tional requirement of Method 6010, so
its effect on data quality was
investigated.
Results and Discussion
This multilaboratory evaluation, of
Method 6010 demonstrates that the
method, as described, is capable of
achieving excellent accuracy and preci-
sion for the determination of the 23
elements in quality control (QC) solu-
tions. These QC solutions contained the
23 elements at concentrations of approx-
imately 100 times the instrumental
detection limits, and the solutions were
interference-free in that no interfering
elements were present at high concen-
trations. Accuracy for the multilaboratory
analyses of the QC solutions (when the
mean values are expressed as a percen-
tage of the target values) varies from 95
percent to 104 percent for the solutions
analyzed without digestion and varies
from 93 percent to 103 percent (silver
excluded) for the solutions digested
before being analyzed. Digestion of the
QC solution containing silver resulted in
a mean silver value that is only 53
percent of the target value whereas the
mean silver value is 100 percent of the
target value for the direct analyses of this
QC solution. The percent RSD's for the"
elements range from 3.1 percent to 9.1
percent for the QC solutions that were
analyzed by Method 6010 without diges-
tion and from 2.6 percent to 13 percent
(when silver is excluded) for the QC
solutions that were analyzed after diges-
tion by Method 3050. The median
percent RSD's for the 2 sets of QC
solutions are 6.5 and 6.7 percent,
respectively. This precision is considered
excellent for these solutions. Silver with
a percent RSD of 52 is the lone outlier
in the QC solution set that was digested
before analysis.
The interlaboratory precision for
Method 6010, with digestion eliminated
as a variable, was determined for the 23
elements in the spiked bulk digests of
six representative solid complex matri-
ces, including river and estuarine sed-
iments and industrial sludges (Table 1).
The analyte concentrations in these
spiked bulk digests were about 100 times
the instrumental detection limits. The
median percent RSD's for the 6 sedi-
ments across 23 elements range from
6.8 percent to 11 percent. Thus, the
precision for the measurement of the
target elements in these complex solu-
tions is very good.
The seventh spiked bulk digest, from
coal fly ash, was spiked with very high
levels of molybdenum and vanadium (0.1
percent). The median percent RSD's for
the determination of the 23 elements in
this spiked digest range from 4.2 percent
to 83 percent with a median of 16 percent
(Table 1). The 12 percent median RSD
for fly ash digests without added Mo and
V (Table 2) suggests that these two
elements decreased the measurement
precision of many of the target elements.
When Method 6010 and Method 3050
are applied in combination for the
determination of the 23 elements in
spiked solids, the apparent measurement
precision decreases (Table 2) when
compared to the corresponding spiked
bulk digest. The median percent RSD's
for the 7 solids across the 23 elements
range from 11-17 percent. The spiked
solid samples were spiked prior to
digestion to assure that the concentra-
tions of the analytes in the resulting
digests were approximately 100 times
greater than the instrumental detection
limits. The accuracy of the ICP Method
6010 can be estimated for these complex
matrices by comparing the average
concentrations of the elements in the
spiked bulk digests (as determined by
Method 6010) to the corresponding
-------
'able 1 . Percent RSD's for the Determination of the 23 Target Elements in the Spiked Bulk Digests
Elements
Al
Sb
As
Be
Cd
Ca
Cr
Co
Cu
Fe
Pb
Mg
Mn
Mo
Ni
Se
Ag
Tl
V
Zn
Ba
A/a
K
Median
Percent
RSD
Hazardous
Waste 1
)1
56
13
5.8
11
8.8
6.2
11
4.4
6.6
15
88
10
20
94
75
44
19
12
9.1
11
17
8.8
10
River
Sediment
19
52
11
5.8
6.6
9.4
5.5
14
4.3
8.3
7.2
81
13
33
89
13
23
13
58
6.7
10
38
7.4
10
Fly
Ash
16
73
83
57
5.7
5.6
36
21
9.7
8.8
22
15
14
19
8.1
16
17
22
7.5
7.6
8.7
49
4.2
16
Estuarine
Sediment
1.9
8.7
22
4.8
7.6
53
7.6
6.8
6.0
6.0
4.7
9.4
11
28
5.4
6.2
46
29
7.3
15
6.4
4.7
4.8
6.8
Industrial
Sludge
11
3.2
25
6.4
3.1
8.5
5.8
6.7
11
6.9
3.9
8.0
11
16
5.1
13
47
30
5.5
10
8.0
5.8
13
8.0
Electro-
plating
Sludge
13
24
8.6
9.9
9.8
7.0
7.8
11
7.8
8.4
5.6
20
9.6
36
9.2
13
19
20
11
2.5
20
9.8
5.8
11
Mine
Tailing
7.6
4.4
5.3
8.5
12
7.9
39
15
12
8.4
8.0
10
5.5
21
12
19
27
29
18
16
11
7.9
7.9
11
Table 2. Percent RSD's for the Determination of the 23 Target Elements in the Spiked Solids
Elements
Al
Sb
As
Be
Cd
Ca
Cr
Co
Cu
Fe
Pb
Mg
Mn
Mo
Ni
Se
Ag
Tl
V
Zn
Ba
Na
K
Median
Percent
RSD
Hazardous
Waste 1
17
27
13
16
13
7.3
79
18
12
14
15
59
14
19
13
13
19
19
18
14
84
14
19
14
River
Sediment
24
56
26
13
84
9.0
22
22
14
19
6.4
8.4
9.0
31
20
9.4
7.6
28
19
12
9.8
40
17
17
Fly
Ash
20
25
16
7.6
9.3
12
9.7
12
10
44
9.6
17
11
24
9.7
9.8
50
34
12
11
7.2
32
18
12
Estuarine
Sediment
22
62
22
11
14
10
7.1
9.2
9.7
16
11
9.0
10
18
10
10
34
28
10
13
14
9.4
18
11
Industrial
Sludge
14
28
20
18
19
12
18
18
19
18
20
16
16
18
20
15
30
18
18
20
16
20
22
18
Electro-
plating
Sludge
18
40
20
7.0
18
14
12
13
9.4
14
19
10
18
43
15
18
27
43
39
8.2
30
15
5.7
18
Mine
Tailing
26
58
22
16
20
12
26
18
12
18
5.8
10
9.4
20
17
12
50
44
24
20
7.2
12
16
18
-------
concentrations which were determined
by AAS by one of the participating
laboratories. A null hypothesis approach
that is based on the mean and on the
corresponding standard deviation was
used to determine if the ICP-AES and
AAS values are significantly different at
the 95 percent confidence level. The
results indicate that only two out of 184
elemental measurements by the two
methods are significantly different. The
ICP-AES mean value was statistically
higher than the AAS value for Ca in the
digests of the Estuarine Sediment and
the Mine Tailing Waste. In some cases
where the ICP/AAS ratios are very
different (less than 0.75 or greater than
1.25), the standard deviations in the ICP
measurements are very high, and, there-
fore, the differences in the means are
not significant. Overall, the agreement
between ICP and AAS is excellent.
The median percent RSD's for the
same 7 solids, unspiked, range from 17-
27 percent (Table 3). This poorer preci-
sion when compared to the spiked solids
results because over 50 percent of the
reported concentration values are less
than 100 times the average of the
instrumental detection limits. In other
words, as the concentrations approach
the instrumental detection limits the
precision decreases as indicated by the
higher percent RSD values. Four ele-
ments among those with the highest
median percent RSD's are antimony,
selenium, silver and arsenic. For those
elements that were present in the digests
of the unspiked solids at concentrations
100 times greater than the IDL's (due to
their occurrence in high concentrations
in the unspiked solids), the precision is
comparable to the precision for the
spiked solid samples.
The Method 6010 variance and the
Method 3050 variance can be calculated
from the data base resulting from the
analyses of the spiked bulk digests and
the spiked solid samples (Table 4). A
statistical analysis of the data shows that
in general, the digestion procedure and
the ICP-AES analytical procedure con-
tribute about equally to the overall
measurement uncertainty or precision
(variance) for the determinations of the
23 target elements in digests of these
7 homogeneous solids.
The method of standard additions was
required for less than 10 percent of the
total analyses. Results by ICP-AES using
the method of standard additions werej
compared with non-MSA data for the
spiked bulk digest samples. The compar-
ison of this limited data set (Table 5)
indicates that on the average there is no
consistent improvement in the data
quality when the method of standard
additions is used with Method 6010 for
the analysis of the solid matrices that
were used in this study.
A comparison between data obtained
on simultaneous and sequential induc-
tively coupled plasma spectrometers
indicated that the concentration values
were statistically indistinguishable.
Recommendations
The experimental design used in this
multilaboratory study has resulted in
several excellent sets of multidimen-
sional analytical data that deserve
consideration beyond the intended scope
of this report. Further analysis and
interpretation of this data base is
suggested.
The presence of high concentrations
(0.1 percent) of added vanadium and
molybdenum in the fly ash spiked bulk
digest could account for the apparent
decrease in the precision of Method 6010
Table 3. Percent RSD's for the Determination of the 23 Target Elements in the Unspiked Solids
Elements
Al
Sb
As
Be
Cd
Ca
Cr
Co
Cu
Fe
Pb
Mg
Mn
Mo
Ni
Se
Ag
Tl
V
Zn
Ba
A/a
K
Median
Percent
RSD
Hazardous
Waste 1
19
38
53
31
37
90
11
24
10
13
80
60
86
30
14
42
41
31
21
14
74
66
23
21
River
Sediment
32
78
48
27
17
13
19
60
9.4
24
12
11
17
42
25
61
43
30
72
12
11
52
34
27
Fly
Ash
19
—
32
27
57
10
28
23
16
52
33
20
24
20
34
—
47
—
15
20
4.3
34
20
23
Estuarine
Sediment
23
—
18
35
52
11
22
12
17
10
37
10
10
58
21
30
1.4
—
17
8.6
14
9.1
17
17
Industrial
Sludge
15
47
83
42
17
10
12
21
17
14
16
18
18
56
16
43
38
38
28
12
24
16
32
18
Electro-
plating
Sludge
23
68
44
70
22
17
12
46
12
12
17
14
21
49
20
74
54
45
35
9.2
38
17
9.6
22
Mine
Tailing
17
57
28
41
59
8.6
90
30
20
18
17
9.2
11
26
40
77
60
120
47
20
8.8
13
24
26
-------
Table 4. Estimated Percentage Contri-
butions of Method 6010 ICP
Variance and Method 3050
Digestion Variance to Total Var-
iance
Elements
Al
Cd
Ca
Co
Cu
Fe
Pb
Mg
Mn
Mo
Ni
Se
Tl
Zn
Ba
K
Be
V
Sb
As
Cr
Na
Ag
Median:
6010
ICP
41
26
50
39
38
11
66
100
68
100
27
89
63
55
37
22
25
24
3
35
26
25
100
46
3050
Digestion
59
74
50
61
62
89
34
0
32
0
73
11
37
45
63
76
75
76
97
65
74
75
0
55
for the determination of many of the 23
target elements in this matrix compared
to the 6 other solid digests. The inter-
fering effects in this matrix should be
studied further.
The poor precision, accuracy, and spike
recoveries for silver-demonstrated in this
study, should be noted in both Method
3050 and Method 6010. The possibility
of precipitation in the nitric/hydrochloric
acid digestion matrix as well as photo-
transformation should be discussed in
Method 3050.
The poor spike recovery of antimony,
observed in this study, should be noted
in Method 3050. In particular, the
possibility of the formation of oxide and
oxo-chloride precipitates of antimony in
the nitric/hydrochloric acid digestion
matrix should be discussed.
The application of the method of
standard additions (MSA), a conditional
requirement of Method 6010, affects the
economics, the turnaround time of
analysis, the practicality of the Method,
as well as the data quality. Although this
report indicates that, on the average,
MSA data were not consistently different
from non-MSA data, the requirement for
the application of the MSA should be
investigated further.
When soil-containing matrices are
being analyzed by Method 6010, the
authors are of the opinion that the MSA
should not be required for those ele-
ments that are endogenous to soils in
high concentrations. The high-
concentration endogenous elements in
soils include Al, Ca, Fe, and Mg.
Table 5. Comparison of MSA and Non-MSA Results"
Spilled Bulk Digests
Non-MSA
Sample Name
Hazardous Waste
Hazardous Waste
Hazardous Waste
River Sediment
Fly Ash
Fly Ash
Fly Ash
Fly Ash
Fly Ash
Fly Ash
Estuarine Sediment
Industrial Sludge
Electroplating Sludge
Mine Tailing
Element
Cd
Tl
Zn
Tl
Cd
Cr
Pb
Mn
Ni
Tl
Tl
Tl
Tl
Cd
N
5
5
5
7
5
5
4
4
3
4
5
5
3
5
Mean
Cone."
894
4410
4310
3160
754
1480
4100
1910
1530
5530
3870
4470
4600
850
SO
117
788
426
2210
422
885
634
233
154
3730
1290
872
740
69
N
3
3
3
3
3
3
4
3
4
3
3
3
4
3
MSA
Mean
Cone."
940
4510
4560
5050
897
2390
6770
1750
1350
1950
3340
4620
5350
985
SO
84
1130
250
675
219
1090
3300
304
500
2470
2850
2230
1120
112
%Ratio
95
98
95
63
84
62
61
109
113
284
116
97
86
86
Dif."
No
No
No
No
No
No
No
No
No
No
No
No
No
No
"Only those elements that required the application of the MSA by three or more laboratories are included as statistically significant.
^Concentration for liquids in fjg/L; concentration for solids in mg/kg.
."Result of a null hypothesis approach used to indicate whether MSA and non-MSA results are significantly different.
N—Number of cases.
% Ratio—non-MSA to MSA mean concentrations.
-------
Table 5. Continued
Unspiked Solids
Non-MSA
Sample Name
Hazardous Waste
Hazardous Waste
Hazardous Waste
Hazardous Waste (Dup j
River Sediment
River Sediment
River Sediment
River Sediment
River Sediment (Dup.)
River Sediment (Dup.)
Fly Ash
Mine Tailing
Mine Tailing
Mine Tailing (Dup.)
Mine Tailing (Dup.)
Mine Tailing (Dup )
Mine Tailing (Dup.)
Electroplating Sludge
Electroplating Sludge
Electroplating Sludge (Dup.)
Electroplating Sludge (Dup.)
Industrial Sludge
Element
Be
Cr
Co
Ni
Sb
Cd
Co
Ni
Cd
Ni
Be
Cd
In
Cd
Co
Ni
Zn
Cd
Mn
As
Mo
As
N
4
6
6
5
6
6
5
6
6
6
6
4
6
4
6
5
6
6
6
6
5
4
Mean
Cone."
0.8
95
8.0
17
325
11
21
44
10
39
3.0
2.3
372
2.4
7.3
21
365
113
226
33
14
11
SD
0.1
8.4
2.4
1.3
266
2.5
16
20
1.6
13
0.8
1.6
44
1.6
2.5
5.6
43
24
31
20
11
6.6
N
3
3
3
4
3
3
4
3
3
3
3
3
3
3
3
4
3
3
3
3
3
3
MSA
Mean
Cone."
0.7
111
9.1
13
169
11
21
27
10
38
2.6
1.9
340
1.5
8.8
21
345
96
254
41
21
26
SD
0.2
10
1.5
8.9
246
3.5
19
7.0
0.7
19
1.2
1.1
119
0.8
3.1
11
122
41
126
20
7.3
11
% Ratio
93
86
88
128
192
103
99
161
107
105
114
122
109
158
83
100
106
118
89
80
68
41
Difc
No
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
Spiked Solids
Non-MSA
Sample Name
Hazardous Waste
Hazardous Waste
Hazardous Waste
Hazardous Waste
Hazardous Waste (Dup.)
Hazardous Waste (Dup.)
Hazardous Waste (Dup.)
Estuarine Sediment
Estuanne Sediment
Estuarine Sediment
Estuarine Sediment
Estuarine Sediment (Dup.)
Mine Tailing
Mine Tailing (Dup.)
Electroplating Sludge (Dup.)
Element
Co
Pb
Mo
Ni
Co
Pb
Ni
Cd
Mo
Ni
Tl
Ni
Ni
Ni
Tl
N
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
Mean
Cone."
45
340
39
57
48
390
61
46
37
65
180
63
64
63
160
SD
8.2
104
20
10
4.8
29
3.5
4.7
19
6.7
65
6.9
7.9
6.9
46
N
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
MSA
Mean
Cone*
30
238
29
37
56
338
58
53
47
73
239
74
60
64
304
SD
2.2
14
2.8
2.9
11
112
14
2.2
2.5
1.3
24
3.3
15
19
104
% Ratio
149
143
134
152
85
115
106
87
79
89
75
86
108
99
53
Dif.c
Yes
No
No
Yes
No
No
No
No
No
No
No
Yes
No
No
Yes
-------
Clifton L. Jones, Vernon F. Hodge, Donald M. Schoengold, Homigol Biesiada,
Thomas H. Starks, and Joseph E. Campana are with the University of Nevada,
Las Vegas, NV 89119-9770.
Thomas A. Hinners is the EPA Project Officer (see below).
The complete report, entitled "An Interlaboratory Study of Inductively Coupled
Plasma Atomic Emission Spectroscopy Method 6010 and Digestion Method
3050." (Order No. PB 88-124 318/AS; Cost: $25.95; subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box93478
Las Vegas. NV 89193-3478
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S4-87/032
#000329
1L
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