OMB First to Final Action Recommendation Checklist 11-12-18

1054 C HANG ET AL .: J OURNAL OF AOAC I NTERNATIONAL V OL . 99, N O . 4, 2016

equation over 90 days, i.e., the pesticides degraded slowly in aged Oolong tea over 3 months. From supplemental Tables 1 and 2, it can been seen that, except for pirimicarb, fenchlorphos, and 4,4ƍ-dichlorodiphenyldichloroethylene (DDE), the other 17 optimized pesticides dropped exponentially or logarithmically over 120 days at a and b concns. At the higher c and d concns, however, all 20 optimized pesticides dropped logarithmically over 90 days. Therefore, it can be concluded that their degradation regularity is in accordance with a logarithmic equation with spray concentration increasing. Prediction of pesticide residues in aged Oolong tea.— The discussion above ( see Degradation Regularity of 20 Representative Pesticides section) indicates that the degradation behavior of the pesticides in aged Oolong tea has certain regularity. However, it should be noted that this process is time consuming for multiple determinations. Therefore, it is necessary to propose a method for predicting the residue of pesticides in aged Oolong tea. Here, we develop and validate a prediction method by taking the raw degradation data of c and d concns. Based on the results of pesticides in aged Oolong tea determined by GC-MS/MS over 90 days (from the raw data of d concn), trend charts (eg, dimethenamid, see Figure 10) were plotted, with determination time (day) on the x -axis and the difference between each measured value and the ¿rst- time-measured value (degradation value) of target pesticides on the y -axis. The logarithmic equations were obtained by ¿tting the 90-day determination results. From these equations, the degradation value of any of the 20 target pesticides at any speci¿c day could be calculated and applied to the raw data generated for that pesticide in a particular laboratory. The logarithmic functions of the 20 pesticides at d concn (listed in Table 3) were applied to predict the residue concentrations of pesticides in aged Oolong tea at c concn. The predicted residue of each pesticide on a particular day could be obtained by subtracting the degradation value of this day from the concentration of the ¿rst day. Accordingly, the residue concentrations of 20 pesticides in aged Oolong tea at different 5-day degradation intervals (days 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90) after spraying at c concn were predicted, and they were compared with the measured results determined by GC-MS/MS ( see Tables 4 and 5). It can be seen from Tables 4 and 5 that the deviation ratios of triÀuralin, teÀuthrin, and dimethenamid were higher as compared to other pesticides at different intervals, with deviation ratio ranges of í23.1 to 21.5, 12.2–26.0, and 6.6–24.0 , respectively. They were followed by pirimiphos-methyl, tolclofos-methyl, and fenchlorphos, with deviation ratio ranges of í2.8 to 21.8, 5.8 to 23.1, and í2.0 to 24.4 , respectively. The remaining 14 pesticides had relatively lower deviation ratios, except for part of the intervals. It can be also seen that the lowest deviation ratios of the 20 pesticides were different. The numbers of pesticides that had the lowest deviation ratios at the 20-, 30-, and 45-day intervals were 4, 9, and 3, respectively. In addition, the highest deviation ratio of 2,4ƍ-DDE, 4,4ƍ-DDE, and bromopropylate was found at days 85, 85 (which were close to the deviation ratios at day 80), and 35, respectively, whereas for all the other pesticides, the highest deviation ratio was found at day 80. This ¿nding could be due to the results at day 80 being abnormal. To evaluate

Practical Application of Degradation Regularity

Degradation regularity of 20 representative pesticides.— The single-laboratory validation results ofAOAC INTERNATIONAL priority research project, “High-Throughput Analytical Techniques for the Determination and Con¿rmation of Residues of 653 Multiclass Pesticides and Chemical Pollutants in Tea by GC/MS, GC/MS/MS and LC/MS/MS: Collaborative Study, First Action 2014.09 ,” showed that the method could be used for determination of as many as 653 target pesticides. 21 To reduce the workload and guarantee a smooth AOAC interlaboratory study, an alternative “shrunken” protocol was proposed by AOAC. Here, using the shrunken protocol, the pesticides commonly used in growing tea, as well as those necessary to be determined for the international tea trade, were selected from the 271 pesticides determined by GC-MS/MS. It should be noted that these pesticides, after being sprayed onto tea, are all of relatively good stability and their polarities are widely representative. On the basis of the degradation equations in supplemental Tables 1 and 2 and discussions regarding them, 20 representative pesticides were optimized ( see Table 1). The degradation regularity of the 20 representative pesticides in aged Oolong tea was studied at c and d concns ( d > c > b > a ) over another 90 days byGC-MS/MS. Similarly, their degradation equations were obtained by plotting the determination time (every 5 days) on the x -axis and the concentration on the y -axis ( see Table 2). It can be seen from Table 2 that the degradation of the 20 representative pesticides agrees well with the logarithmic

Table 1. Retention time and monitored ion transitions for the 20 pesticides by GC-MS/MS

Quantifying precursor/product ion transition

Qualifying precursor/product ion transition

Retention time, min

No.

Pesticide

ISTD Heptachlor epoxide

22.15

353/263

353/282

1 2 3 4 5 6 7

7ULÀXUDOLQ 7HÀXWKULQ

15.41

306/264 177/127 200/199 173/145 238/166 230/154 287/272 267/252 290/233 318/248 359/303 318/248 283/96 335/173 237/208 408/59 148/105 181/166 266/218 341/185

306/206 177/101 183/102 173/109 238/96 230/111 287/242 267/93 290/125 318/246 359/331 318/246 283/255 335/303 237/182 408/363 148/79 181/165 266/246 341/183

17.4

Pyrimethanil

17.42

Propyzamide 18.91

Pirimicarb

19.02

Dimethenamid 19.73 Fenchlorphos 19.83

8 Tolclofos-methyl

19.87

9 Pirimiphos-methyl 20.36

10

ƍ ''( 22.79

11 Bromophos-ethyl

23.16

12

ƍ ''(

23.9

13 Procymidone 24.7 14 Picoxystrobin 24.75

15 16 17 18 19

Quinoxyfen 27.18

Chlorfenapyr

27.37 27.66 28.63

Benalaxyl Bifenthrin

'LÀXIHQLFDQ 28.73

20 Bromopropylate 29.46