2. AOACRIChemContMethods-2018Awards

1450 Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015

for quantification, and this thinking is very meticulous and scientific, which is worth learning from. Laboratory 26: We can’t develop the instrumental condition for chlorfenapyr because m / z 408 in chlorfenapyr is low sensitivity. Study Director response: m / z 408 in chlorfenapyr is the ion recommended in the collaborative method. No similar problems have been found when determining this ion by other laboratories. Our review of data provided by this laboratory has found that the precursor ion monitored by Laboratory 26 was m / z 480, so it is judged that the cause of this problem might be that this laboratory entered wrongly 480 for 408 when the method was established. Therefore, it can be said the cause was this mistake. Laboratory 28: No results for 2,4′-DDE due to falsely determined MRM acquisition window. Study Director response: When using GC/MS determination of tolclofos-methyl by the afore-mentioned Laboratory 28, only part of peaks were integrated for the target pesticide owing to errors with setting of the MRM acquisition window, leading to absence of test results. At the time of GC/MS/MS determination by the laboratory, they made the mistake again when setting the 2,4′-DDE MRM window. They established the collection method according to the retention time of 4,4′-DDE, resulting in no detection of 2,4′-DDE, and we also feel the result was caused by this mistake. (c)  Regarding LC/MS/MS analysis.— Laboratory 17: For the chromatography, our experience is that the maximum injection volume on an Acquity column is 5 μL. The 10 μL injection to follow your method could explain some bad chromatographic peak shape; it was difficult to obtain R 2 >0.995. For several pesticides one calibration point has to be removed (clearly an outlier), but even with four points of calibration, the 0.995 criterion was not always satisfied. The Study Director considers their experience is due to the maximum injection volume being 5 μL for their chromatograph, while 10 μL injection was adopted in the collaborative study method, causing certain pesticide chromatograph peak shapes to worsen. Laboratory 17 also states that they eliminated the point of obvious deviation for calibration curves of some compounds in the specific determinations so as to ensure R 2 to reach 0.995. However, although the four-point calibration curve was adopted, the criterion of R 2 >0.995 could not be met. The Study Director considers the injection quantity mainly

depends on the sensitivity of instrument, and the instrument used by Laboratory 18 has very high sensitivity; the sample was diluted five times before injection for determination. It is also acceptable that the 5 μL injection adopted by Laboratory 17 can satisfy the technical indexes of the method. Regarding the criteria of R 2 ≥0.995 being hard to meet, there are 2113 R 2 values submitted by 30 collaborators, with 2059 in conformity with the criterion of R 2 >0.995, accounting for 97%. As for this requirement, it should be strengthened in future collaborative studies, and in so doing, the accuracy of the quantification of target pesticides will be greatly increased while measuring errors will be reduced, minimizing outliers. Laboratory 18: Before injection, the samples were diluted five times with acetonitrile–water (3 + 2, v/v) because the system is very sensitive and we have some pesticides that were saturated. Study Director response: The Agilent 6490 adopted by this laboratory is the latest model of the Agilent triple quadruple mass spectrometer. This instrument adopts the i-funnel technique, about 10 times higher than the sensitivity of the 6460 instrument. Therefore, it is understandable that dilution is needed before injection. At the same time, it is also found that Laboratory 22 used the old instrument from the 1990s, and its sensitivity is relatively low. To ensure the calibration curve reached above R 2 >0.995, it adopted the method of increasing the injection volume to solve the problems encountered in the experiment. Laboratory 18 used the dilution approach to solve the problems encountered, while Laboratory 22 used the method of increasing the injection volume to solve the problems encountered. In summary, Laboratories 18 and 22 investigated the ruggedness of the method in two aspects. Based on consideration of the method principle, they used their skills to tackle the practical problems encountered in the experiment, which is advisable and praiseworthy. Laboratory 23: Retention times slightly change from the green tea to the oolong tea matrix. A column has been added to show the exact retention time for both of the matrixes. Study Director response: When using LC/MS/MS for respective analysis of green tea and oolong tea samples, the laboratory discovered that there existed a system difference of 0.03 s maximum for retention times of pesticides in the two matrixes. Laboratory 23’s observation for the experiment was so sharp that we should learn from their meticulous scientific research attitude. Because green tea and oolong tea are manufactured with different processing technologies, the

Table 13. Method efficiency for determination of 20 pesticides in incurred green tea by GC/MS, GC/MS/MS, and LC/MS/MS

GC/MS (16 laboratories)

No.

Pesticide

No. of labs

Avg. C., μg/kg

S r

, μg/kg

RSD r

, % S R

, μg/kg

RSD R

, %

HorRat

1 2

Pyrimethanil

13 15

613.3

20.2

3.3 4.0

74.5 17.9

12.2 23.0

0.7 1.0

Bifenthrin

77.8

3.1

GC/MS/MS (14 laboratories)

1 2

Pyrimethanil

12 14

575.4

32.2

5.6 5.6

80.9 17.5

14.1 22.2

0.8 0.9

Bifenthrin

78.6

4.4

LC/MS/MS (24 laboratories)

1 2 3

Acetochlor Triadimefon Trifloxystrobin

22 24 24

14.1 41.3 90.7

1.4 4.4 7.6

9.8

3.3 8.9

23.6 21.6 21.3

0.8 0.8 0.9

10.6

8.4

19.4