2. AOACRIChemContMethods-2018Awards

S chneider & A ndersen : J ournal of AOAC I nternational V ol . 98, N o . 3, 2015  665

Table 4(a). CC α

and CC β

for triphenylmethane dyes and metabolites in seafood matrix CCα, μg/kg

CC β

, μg/kg

MG

LMG

CV

LCV

BG

MG

LMG

CV

LCV

BG

Salmon

0.24

0.17

0.18

0.29

0.35

0.27

0.19

0.20

0.33

0.38

Catfish

0.27

0.17

0.21

0.15

0.41

0.31

0.19

0.24

0.17

0.45

Shrimp

0.29

0.14

0.32

0.28

0.43

0.33

0.16

0.36

0.32

0.49

Table 4(b). MDL and LOQ for triphenylmethane dyes and metabolites in seafood matrix MDL, μg/kg

LOQ, μg/kg

Salmon

0.12

0.07

0.07

0.11

0.21

0.47

0.27

0.26

0.45

0.85

Catfish

0.13

0.06

0.12

0.12

0.30

0.53

0.24

0.47

0.47

1.22

Shrimp

0.33

0.09

0.23

0.09

0.34

1.35

0.38

0.91

0.35

1.35

BG treatment bath for 1 h (12). By comparison, the salmon and catfish incurred for this collaborative study were exposed to only 2 µg/L of BG for 1 h.

correlation for the remaining five calibrants. In three instances (CV in catfish for one laboratory, MG and BG in shrimp for another), linear correlation could not be achieved by deletion of a single calibration point. For these three, all data reported by the laboratory for the particular analyte in the particular matrix were omitted from the statistical analysis.

Preliminary Data Analysis

All reported data were compiled and examined for validity. Data were omitted for cause when participants reported specific difficulties, such as a sample being lost due to spillage, or inadvertent combination with another sample. While Method 2012.25 allows the measure of linear correlation to be as low as R 2 = 0.95, in this collaborative study, single outlier calibration points were excluded from the calibration when R 2 was less than 0.99 and the omission of one point would result in R 2 ≥0.99

Statistical Analysis

A determination of repeatability and reproducibility was performed using the AOAC International Interlaboratory Study Workbook for Blind (Unpaired) Replicates, v. 2.1 (14), which was developed to implement the AOAC INTERNATIONAL guidelines for the AOAC Official Method Program (15).

Table 5. Comparison of the accuracy (trueness and precision) of 0.9 µg/kg fortified samples using three different calibration methods for residue quantification; data represents duplicate matrix spikes from 10 laboratories ( n = 20) MG LMG CV LCV BG Trueness, (avg. recovery, %) RSD, % Trueness, (avg. recovery, %) RSD, % Trueness, (avg. recovery, %) RSD, % Trueness, (avg. recovery, %) RSD, % Trueness, (avg. recovery, %) RSD, % Salmon Extracted matrix a 95.3 17.7 101.1 11.9 99.5 8.7 102.4 8.8 99.1 14.8

Post-extraction fortified matrix b

96.8

19.2

112.4

11.3

113.4

8.4

116.5

11.0

162.8

28.0

Solvent c

84.6

14.6

101.2

18.5

104.1

10.5

103.2

10.8

128.4

40.3

Catfish

Extracted matrix

77.5

24.2

107.7

6.3

101.8

8.6

105.2

6.7

90.4

26.2

Post-extraction fortified matrix

88.8

22.9

116.2

5.7

115.1

6.0

115.2

4.7

163.2

30.5

Solvent

79.3

25.9

104.2

7.4

113.1

10.8

95.5

18.8

140.1

42.6

Shrimp

Extracted matrix

95.3

17.7

105.4

7.8

105.6

15.9

105.9

5.6

101.0

24.7

Post-extraction fortified matrix

105.5

15.3

118.2

7.2

125.7

21.0

113.3

7.0

145.2

19.5

Solvent 27.6 a  Matrix fortified at calibration concentrations and then extracted to produce a set of six standards: 0, 0.25, 0.5, 1.0, 2.5, and 5.0 µg/kg (tissue equivalent d ). b  Calibration standard based on one portion of tissue extracted and the matrix extract fortified at a concentrations of 1.0 µg/kg (tissue equivalent). c  Six standards prepared in solution at tissue equivalent concentrations. d  Concentrations are equivalent to the amount present in the 2 g sample portion. Method results in a 2.5-fold concentration of residues in the extracts. 92.9 14.5 102.0 12.0 117.8 27.8 102.9 19.7 120.3