AOAC RI Chemical Cont. Methods-2018 Awards

Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015  1451

Table 14. Distribution range of RSD r

, RSD R

, and HorRat values for incurred samples

Parameters of method efficacy

RSD r

, %

RSD R

, %

HorRat

Range

<8

8–15

>15

<16

16–25

>25

<0.50 0.50–1.00 1.01–2.00 >2.00

GC/MS (16 laboratories)

2(100) a

Green tea

0

0

1(50)

1(50)

0

0

2(100)

0

0

GC/MS/MS (14 laboratories)

Green tea

2(100)

0

0

0

2(100)

0

0

2(100)

0

0

LC/MS/MS (24 laboratories)

Green tea

0

3(100)

0 0

0

3(100)

0 0

0 0

3(100) 7(100)

0(0) 0(0)

0 0

Total

4(57)

3(43)

2(29)

5(71)

a Data in parentheses are the percentages.

two teas have totally different matrixes. Owing to the different matrixes, the system deviation of 0.03 s maximum for pesticide retention time is normal and will not affect the test results. Here, we mainly focus on learning from Laboratory 23’s pursuit of meticulous scientific experimentation. Laboratory 24: In case of contents of 10 μg/kg peak areas below the areas of the lowest calibration point; oolong tea: after dissolution of the residues orange and oily drops, the solution is light yellow and clear. After membrane filtration solution clear. Study Director response: Our review of the collaborative study result table provided by this laboratory has found that the detection concentrations for the two compounds triadimefon and trifloxystrobin in green tea incurred samples from this laboratory turned out to be 40–50% lower than those from other laboratories, from which we judge that the determination results of acetochlor are lower than 10 μg/kg, so no specific detection results are reported. For this problem, we also found that similar things happened with Laboratory 21. Based on the above-mentioned descriptions, Laboratory 24 also discovered that there are orange and oily drops with oolong tea pesticide extraction solutions, which became clear after filtration membrane. We also encountered such a phenomenon, which is normal and will not affect test results. Laboratory 25: For oolong tea, had to increase amount of extraction solution to get a better extraction. For oolong tea, the high standard (the fifth point) had to be removed to have a good calibration fit (picoxystrobin, indoxacarb, chlorpyrifos, and butralin). For oolong tea, used linear 1/x to give more weight to lower standard. Study Director response: Laboratory 25 proposed increasing the amount of extraction solution to get a better extraction for pesticides in oolong tea, and the Study Director has not discovered similar problems from other laboratories. The Study Director considers that pesticide extraction efficiencies have a lot to do with choice of extraction solutions and amount as well as extraction equipment used. As for the homogenizer recommended in this collaborative study method, we compared the efficiencies of three-time extraction and two-time extraction. Our findings are that two-time extraction will suffice for the requirements of recovery indexes. If Laboratory 25 found that a two-time extraction cannot suffice for good recoveries, an additional extraction may also be conducted. For calibration curves of

oolong tea, the high concentration points with deviations for picoxystrobin, indoxacarb, chlorpyrifos, and butralin are eliminated from their own calibration curves so as to obtain better calibration curves, which is feasible. For oolong tea, using liner 1/x gave more weight to lower stand. Laboratory 28: No results for butralin due to constant signals in the given MRM transitions. Study Director response: Regarding no detection of butralin, our fault is the major cause for the problem. Because instruments from Waters are unavailable in our laboratory, the precursor ion m / z 337 of butralin given by a local employee from Waters was not verified, so using 337 is a mistake. In this collaborative study, Laboratories 9, 22, 29, and 25 also used instruments fromWaters, and they found 337 is a mistake through scanning, and the correct one should be 296. Therefore, an accurate determination was conducted on butralin. In terms of learning this lesson, the correct ion information can be obtained and such mistakes can be discovered by scanning the target pesticides when encountering similar problems in future experiments. If it was handled like this, this problem could have been solved earlier. Having said this, the Study Director is not shirking responsibility but discussing the problem encountered in order to find out scientific thinking and solve the problem. In a word, as the Study Director said before, it is our fault and we caused the trouble to the laboratory involved. First, review of 6868 test data and related information from 30 laboratories has found that one laboratory deviated from the collaborative study operational procedures by not undertaking the pre-study, leading to a great deal of outliers from its sample inspection; this laboratory was eliminated. A total of 6638 data from the remaining 29 laboratories are effective results and were inspected with Grubbs and Dixon test to eliminate 187 outliers, making up 2.8% of the total effective data, of which 1977 were test data from GC/MS determination, with 65 outliers detected, making up 3.3%; 1704 test data were from GC/MS/MS determination, with 65 outliers detected, accounting for 3.8%; and 2957 test data were from LC/MS/MS determination, with 57 outliers detected, making up 1.9%. Conclusions This collaborative study is one of the priority research items of AOAC in 2010 and a significant systematic project of three features as follows: