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Thompson et al.:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
6, 2015
Table 2. Linearity determination—average of duplicate results from 3 separate days (
n
= 3). These determinations were
performed after calibration with the standards listed in Table 3
Element
Parameter
Na
a
Expected value, mg/L 0.25
0.50
0.75
1.25
1.5
5.0
10
15
30
Overall recovery, % 102.1
104.7
104.0
105.7
105.2
102.4
101.5
100.5
100.1
Overall RSD, % 5.3
2.9
2.1
1.2
1.9
0.6
0.3
1.4
1.4
Mg
a
Expected value, mg/L 0.10
0.20
0.30
0.50
0.60
2.0
4.0
6.0
12.0
Overall recovery, % 98.9
101.8
103.7
102.9
101.3
100.5
101.1
99.4
99.3
Overall RSD, % 4.6
1.9
2.5
1.8
0.6
0.7
1.6
1.1
1.1
P
a
Expected value, mg/L 0.25
0.50
0.75
1.25
1.5
5.0
10.0
15.0
30.0
Overall recovery, % 94.8
97.6
93.0
93.4
91.1
93.9
96.1
97.3
93.8
Overall RSD, % 5.9
1.2
7.5
1.3
9.3
8.1
7.8
0.5
8.0
K
a
Expected value, mg/L 0.50
1.0
1.5
2.5
3.0
10.0
20.0
30.0
60.0
Overall recovery, % 98.2
100.3
101.5
103.1
101.8
102.9
102.2
101.4
100.9
Overall RSD, % 6.9
2.6
3.1
3.7
2.3
3.2
3.2
4.2
4.0
Ca
a
Expected value, mg/L 0.50
1.0
1.5
2.5
3.0
10.0
20.0
30.0
60.0
Overall recovery, % 97.8
99.9
100.5
102.1
100.7
100.9
102.1
100.6
101.1
Overall RSD, % 5.5
2.5
1.8
3.0
1.1
2.7
3.2
3.7
3.0
Cr
a
Expected value, μg/L 0.40
0.80
1.2
2.0
2.4
8.0
16.0
24.0
48.0
Overall recovery, % 100.2
100.1
102.0
101.5
103.0
101.8
101.5
100.9
98.9
Overall RSD, % 7.2
5.4
0.5
1.6
1.8
1.0
0.6
1.2
2.7
Mn
a
Expected value, mg/L 0.0025
0.005
0.0075 0.0125
0.015
0.050
0.10
0.20
0.30
Overall recovery, % 99.9
101.1
101.7
102.3
101.9
101.9
102.4
101.4
99.6
Overall RSD, % 5.8
3.1
1.2
1.2
0.8
1.5
1.6
1.2
1.2
Fe
a
Expected value, mg/L 0.025
0.050
0.075
0.125
0.15
0.50
1.0
1.5
3.0
Overall recovery, % 105.0
106.1
106.7
106.5
106.6
105.5
104.7
99.4
98.3
Overall RSD, % 8.9
7.1
4.1
2.9
3.3
4.3
5.0
1.7
1.4
Cu
a
Expected value, mg/L 0.0025
0.005
0.0075 0.0125
0.015
0.050
0.10
0.20
0.30
Overall recovery, % 101.6
101.9
101.1
102.9
101.9
101.6
100.4
99.3
96.3
Overall RSD, % 6.8
6.1
3.2
2.8
2.8
1.9
1.8
3.0
3.1
Zn
a
Expected value, mg/L 0.010
0.020
0.030
0.050
0.060
0.20
0.40
0.60
1.2
Overall recovery, % 98.6
100.6
99.5
101.1
100.6
99.7
101.2
100.0
98.1
Overall RSD, % 7.6
6.6
1.9
2.1
2.9
2.0
1.5
2.0
2.0
Mo
a
Expected value, μg/L 0.40
0.80
1.2
2.0
2.4
8.0
16.0
24.0
48.0
Overall recovery, % 97.7
101.2
103.7
98.3
100.7
100.7
100.6
99.7
98.8
Overall RSD, % 7.5
2.9
4.0
3.5
0.8
1.3
1.2
2.2
2.2
Se
b
Expected value, μg/L 0.20
0.40
0.60
1.0
1.2
4.0
8.0
12.0
24.0
Overall recovery, % 100.0
97.3
98.2
96.6
99.4
100.0
99.0
99.4
99.9
Overall RSD, % 3.4
2.8
2.0
3.3
1.4
1.2
0.5
2.2
1.2
a
He gas mode; Ge ISTD.
b
H
2
gas mode; Te ISTD.
unfit for validation work. Most elements demonstrated RSD
iR
<5% for all matrixes, which is quite remarkable considering
the opportunities for variability in the study design. There is no
SMPR for intermediate precision, but these data suggest that the
method would perform well in a collaborative study, and this
proved to be the case (
see
below).
The cases for Fe, Cu, and Mn are discussed under LOQ.
There were no SPIFAN matrixes that really challenged the
method anywhere near the required lower analytical range for
these elements, and no low-level spikes were performed.
Precision data from SRM 1849a are shown in Table 5. The
SRM was analyzed nine times, on different days and yielded
RSD
iR
of <3% for all elements.
Recovery/Accuracy
The SMPR designates a recovery of 90–110% over the range
of the assay, and 80–115% for low levels of Mn. Table 6 shows
the recovery of each element in each SPIFAN matrix measured
in triplicate over each of 3 days. The spikes were added at
approximately 100% of the nominal element concentration, and
the triplicate means on each day were averaged to one result
75