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1716

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