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

C HANG ET AL .: J OURNAL OF AOAC I NTERNATIONAL V OL . 99, N O . 4, 2016 1051

120 days, showing only as scatter points (R 2 <0.4); and F—no trend over either 40 or 120 days, showing only as scatter points (R 2 <0.4). In addition, ¿ve pesticides were not detected at either a or b concn. The degradation regularity of 271 pesticides was studied according to the A–F trends. The ratios of pesticides associated with degradation trends A–F in the 271 pesticides are shown in Figure 1. It was observed that most of the pesticides followed the A, B, or E degradation trends. At a concn, the ratios for A, B, and E were 21.8, 35.1, and 24.4 , respectively, and their total number was 220, accounting for 81.2 of the 271 pesticides. At b concn, the ratios for A, B, and E were 25.5, 33.9, and 14.8 , respectively, and their total number was 201, accounting for 74.2 of the 271 pesticides. These results demonstrate that A, B, and E degradation trends could represent the main aspects of the 271 pesticides. That is, most of the pesticides dropped exponentially over 40 days, and they presented dropping trends exponentially or logarithmically over 120 days. Although the ratios of pesticides with other degradation trends were small, they did represent a certain degree of degradation regularity. Therefore, all trends (A–F) are discussed below. Degradation trend A.— Taking propachlor as an example, trend A degradation rates over 40 and 120 days are shown in Figure 2a and b, respectively. It is clearly observed that the concentration of propachlor in aged Oolong tea exponentially decreased with the increase of intervals. It is indicated that the degradation kinetics of trend A is a ¿rst-order reaction by Equation 1: where C is the concentration of each pesticide in aged Oolong tea, C 0 is the initial concentration of each pesticide in aged Oolong tea, k is degradation rate constant, and t is the determination time (day). It can be concluded that without the inÀuence of other factors, the degradation rate of pesticides in trend A has a direct ratio to the initial concentration of pesticides in aged Oolong tea. Based on the ¿rst-order reaction model, the half-life of pesticides in trend A could be calculated by Equation 2: ln2 2 1 2 t k ) ( = is the half-life of the determined pesticide. Half-lives were calculated according to the degradation equations of pesticides in trend A listed in supplemental Table 1 where t 1/2 e 1 0 - C C kt = ) (

Extraction

Weigh 5 g dry tea powder (accurate to 0.01 g) into a 80 mL centrifuge tube, add 15 mL acetonitrile, and homogenize at 13500 rpm for 1 min. Centrifuge the mixture at 2879 × g for 5 min, and transfer the supernatant into a pear-shaped Àask. Re- extract the residue with 15 mL acetonitrile and centrifuge the mixture. Combine the two extracts, and rotary evaporate in a water bath at 40°C to about 1 mL for cleanup. Place a pear-shaped Àask under the ¿ve-port Àask vacuum manifold, and mount a Cleanert TPT cartridge onto the manifold. Add about 2 cm anhydrous sodium sulfate onto the Cleanert TPT cartridge packing material, prewash with 10 mL acetonitrile–toluene (3 1, v/v) and discard the efÀuents to activate the cartridge. Stop the Àow through the cartridge when the liquid level in the cartridge barrel has just reached the top of the sodium sulfate packing. Discard the waste solution collected in the pear-shaped Àask and replace with a clean pear-shaped Àask. Transfer the concentrated sample extract ( see Extraction section) into the SPE cartridge, rinse the sample solution bottle with 2 mL acetonitrile–toluene (3 + 1, v/v), and repeat this step thrice, transferring the rinsing liquids to the cartridge. Attach a 50 mL storage device onto the cartridge, and then elute with 25 mL acetonitrile–toluene (3 + 1, v/v), collecting the efÀuent into the pear-shaped Àask by gravity feed. Rotary evaporate the efÀuent in a water bath at 40°C to about 0.5 mL. Add 40 ȝL heptachlor epoxide ISTD to the sample. Evaporate to dryness under a stream of nitrogen in a 35°C water bath. Dissolve the dried residue in 1.5 mL hexane, ultrasonicate the sample to mix, and ¿lter through a 0.2 ȝm membrane ¿lter. The sample is ready for GC-MS/MS analysis. Cleanup The residues of 271 pesticides in aged Oolong tea were determined 25 times by GC-MS/MS over 120 days (every 5 days) to monitor their degradation behavior. To study the degradation regularity of the 271 pesticides in aged Oolong tea, scatter diagrams at a and b spray concentrations ( a and b concns) over 40 and 120 days were prepared, using determination days as horizontal ordinates and concentrations of pesticide residues as vertical ordinates. The degradation equations are summarized in supplemental Table 1 (at a concn) and supplemental Table 2 (at b concn). By comparing the degradation equations of pesticides at a and b concns over 40 and 120 days, it was found that their degradation trends were different. The trends included the following aspects: A—the residues of pesticide dropped exponentially over both 40 and 120 days; B—the residues of pesticide dropped exponentially over 40 days and logarithmically over 120 days; C—the residues of pesticide dropped logarithmically over 40 days and logarithmically/polynomially over 120 days; D—no trend over 40 days, showing only as scatter points (R 2 <0.4), although a dropping trend was seen over 120 days; E—some dropping trend over 40 days, whereas no trend over Results and Discussion Degradation of 271 Pesticides in Aged Oolong Tea

Figure 1. Percentage of pesticides in accordance with degradation trends A–F in 271 pesticides at a and b concentrations. Values represent the number of pesticides in accordance with each trend multiplied by 100 and divided by the total number (271) of pesticides (% = n × 100/ N ).