2. AOACRIChemContMethods-2018Awards

Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015  1437

been certified proficient to participate in the collaborative study by the Study Director were considered for further analysis and interpretation ( see Annex 1.2 on the J. AOAC Int. website). (a)  Application of the Dixon and Grubbs outlier tests on 6638 data generated .—The Dixon and Grubbs tests were used to examine outliers in the 6638 data from the remaining 29 laboratories. For GC/MS, 65 outliers out of 1977 test data were identified, accounting for 3.3%. For GC/MS/MS, 65 outliers out of 1704 test data were identified, accounting for 3.8%. For LC/MS/MS, 57 outliers out of 2957 LC/MS/MS test data were identified, accounting for 1.9%. Therefore, a total of 187 outliers, making up 2.8% of the 6638 data were identified and eliminated from the data package. (b)  Method extraction efficiency and reproducibility for fortified samples .—The recovery efficiency and reproducibility of the GC/MS, GC/MS/MS, and LC/MS/MS methods for the analysis of the 20 selected pesticides in oolong and green tea are presented in Tables 4–6. Further analysis of the method efficiency parameters such as Rec. (recovery), RSD R , RSD r , and HorRat values were summarized in Table 7. ( 1 )  By GC/MS.— For green tea or oolong tea, the average recoveries (% Avg Rec.) for the fortified samples by GC/MS fall within the range of 75–100%, RSD r <8%, accounting for 100%. For green tea samples, the pesticides with RSD R <16% accounted for 100%. For oolong tea samples, the pesticides with RSD R <25% accounted for 100%. The HorRat values for all the pesticides were less than 2.0. ( 2 )  By GC/MS/MS.— For green tea or oolong tea, the average recoveries (%Avg Rec.) for the fortified samples by GC/MS/MS fall within the range of 75–100%, RSD r <8%, accounting for 100%. For green tea samples, the pesticides with RSD R <16% accounted for 100%. For oolong tea samples, the pesticides with RSD R <25% accounted for 90%. There were two pesticide residues for which the RSD R exceeded 25%, accounting for 10%. The HorRat values for all the pesticides were less than 2.0. ( 3 )  By LC/MS/MS.— For green tea or oolong tea, the average recoveries (%Avg Rec.) for the fortified samples by LC/MS/MS fall within the range of 75–100%, RSD r <15%, accounting for 100%. For green tea samples, the pesticides with RSD R <16% accounted for 95%, and one pesticide had RSD R more than 25%, accounting for 5%. For oolong tea samples, the pesticides with RSD R <25% accounted for 75%. There were five pesticide residues for which the RSD R exceeded 25%, accounting for 25%. The HorRat values for all the pesticides were less than 2.0. According to Evaluation of Collaborative Study Results , b ( 2 ) and b ( 3 ), there were seven pesticide residues (two pesticides analyzed by GC/MS/MS and five pesticides analyzed by LC/MS/MS) for which the RSD R exceeded 25%. The low precision for the analysis of these seven pesticide residues may be explained by the fact that the concentrations of the pesticides added to oolong tea were determined to be too close to the LOD of the older generation instruments used in the analysis. It was with these older generation instruments that the method generated significant variability in precision. Additionally, the concentration of seven compounds added to oolong tea were low and close to the lowest concentration point on the calibration curve, thus contributing to the imprecision at the low end of the calibration curve. For example, this happened in the case of Laboratory 25, which determined that

Results and Discussion Evaluation of Collaborative Study Results In 2010, the multiresidue determination method for 653 pesticides in tea was selected to be one of the priority study projects of AOAC. After 3 years of preparation, 30 laboratories from 11 countries and regions participated in this collaborative study from March 1 through June 30, 2013 to evaluate the reproducibility of the method. A total of 560 samples were analyzed including green tea and oolong tea fortified with 40 selected pesticides, aged oolong tea, and pesticide incurred green tea. Participants had the option to use one or more of the three available instrumental analytical techniques, GC/ MS, GC/MS/MS, and/or LC/MS/MS, for the analysis. Thirty laboratories submitted results to the Study Director ( see Table 2, and the details can be found in Annex 1.2 available on the J. AOAC Int. website). The first three columns in Table 2 report the total number of pesticide residues (6868) detected by the 30 laboratories. The last three columns report the number of results (8915) submitted by the 29 participating laboratories for the precollaborative study. For GC/MS, the results of target pesticides and precollaborative study were 1977 and 2740, respectively. For GC/MS/MS, the results of target pesticides and precollaborative study were 1808 and 2440, respectively. For LC/MS/MS, the results of target pesticides and precollaborative study were 3083 and 3735, respectively. Note that Laboratory 20 did not submit any precollaborative study results to the Study Director. Columns 4–6 report a total of 41238 ions monitored, columns 7–9 report the total ion abundance data (23205), and columns 10–12 report the total number of calibration data points (2233) generated in the collaborative study. A review of the 6868 test data and related information submitted to the Study Director from the 30 laboratories revealed that one laboratory (Laboratory 20) had not submitted precollaborative test results to the Study Director but had gone ahead and conducted the collaborative study. Since this laboratory had failed to meet the prerequisite proficiency criterion for entering into the collaborative study, the data submitted by this laboratory were not included in the collaborative data package. A cursory analysis of an example calibration data generated by Laboratory 20 shown in Table 3 for oolong tea immediately revealed that there were too many significant deviations ≥20% between the measured and the expected concentrations, demonstrating that the laboratory had not achieved the requisite proficiency level required for the collaborative study and would not have been qualified to participate in the analysis of the real samples. Therefore, only 6638 results from the 29 laboratories that had met all the precollaborative data requirements and had Table 2014.09H. Recommended maximum permitted tolerances for relative ion intensities using a range of mass spectrometric techniques Relative intensity (% of base peak), % GC/MS (relative), % GC/MS/MS, LC/MS/MS (relative), % >50 ±10 ±20 >20–50 ±15 ±25 >10–20 ±20 ±30 ≤10 ±50 ±50