AOAC RI Chemical Cont. Methods-2018 Awards

Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015  1443

Table 7. Distribution ranges for recovery, RSD r

, RSD R

, and HorRat values for fortified tea samples

Parameters of method efficiency

Recovery, %

RSD r

, %

RSD R

, %

HorRat

Range

<75 75–100 >100

<8

8–15 >15 <16 16–25

>25

<0.50 0.5–1.0 1.01–2.0 >2.0

GC/MS (16 laboratories)

40(100) a 40(100)

Green tea Oolong tea

0 0

0 0

20(100) 20(100)

0 0

0 20(100) 0 6(30)

0

0 0

17(85)

3(15)

0

0 0

14(70)

0 19(95)

1(5)

GC/MS/MS (14 laboratories)

Green tea Oolong tea

0 0

40(100) 40(100)

0 0

20(100) 20(100)

0 0

0 20(100) 0 12(60)

0

0

8(40) 3(15)

12(60) 15(15)

0

0 0

6(30)

2(10)

2(10)

LC/MS/MS (24 laboratories)

Green tea Oolong tea

0 0 0

40(100) 40(100) 240(100)

0 0 0

18(90) 16(80) 114(95)

2(10) 4(20)

0 19(95) 0 1(5)

1(5)

0

8(40)

12(60) 18(90)

0

0 0

14(70)

5(25)

1(5)

1(5) 4(3)

Total 0 a  Number (percentage): the number accordance with the range (percentage of the number accordance with the range in the total number of determined pesticides). 6(5) 0 78(65) 35(29) 7(6) 37(31) 79(66)

with time and to determine the effect it has on the quantitative analysis of pesticides in tea samples. The studies concluded that pesticides will decrease in concentration by approximately 4.3–31.1% over a 3 month period. Accordingly, correlation equations were derived for the degradation rate in concentration and have been defined for each of the pesticides (Figure 2) under study so that the concentration degradation factor can be considered in the calculation of the concentration of a pesticide at any specified time during a study. On the basis of stability results of pesticides in aged oolong tea determined by GC/MS/MS or LC/MS/MS in a continuous 3 month study, trend charts were plotted in which the determination time (day) was the X-axis and the difference between each concentration determined at time t and the concentration of pesticide estimated at time zero was the Y-axis. The logarithmic equations presented graphically in Figure 3 were obtained by fitting the 3 month determination results. From these equations, the degradation value of any of the 20 target pesticides at any specific day could be calculated and applied to the raw data generated for that pesticide in that particular laboratory. In this collaborative study, the total length of time for all laboratories to complete the analysis, which began March 28, 2013 and ended June 27, 2013 was 120 days. Therefore, based on the day of analysis, it would be possible to calculate the degradation rate for each of the 20 pesticides in the study from the logarithmic equation defined for each pesticide. To eliminate the influence from the natural degradation of pesticides, the rates of decrease in concentration for each pesticide residue measured in each laboratory were pooled together into a database from which correlation equations were derived. The procedure was used to calculate corrected/revised method efficiency parameters as shown in Table 11 for oolong tea. Table 11 shows that of the method performance parameters such as S r , RSD r , S R , RSD R , and HorRat, only the RSD R data are impacted significantly by the degradation factor. So, only the raw data and corrected data of RSD R as shown in Table 12 will be discussed. In the previous discussion, it was noted that only six of the 20 pesticides analyzed by GC/MS/MS showed RSD R ≤25%, while the other 14 pesticides had RSD R ≥25%. Application of

the degradation correction factor to the previous data results in a revised RSD R with an average of 22.8%, and the RSD R of the remaining 14 pesticides was RSD R ≤25%. A similar trend was observed for the 70% of the pesticides analyzed by LC/MS/MS that showed RSD R >25%. In conclusion, it is the way the samples are prepared rather than any inherent weaknesses in the method that accounts for the unexpected large RSD R data for some of the selected pesticides. (d)  Method extraction efficiency and reproducibility for incurred samples .—The method efficiency parameters such as Rec., RSD r , RSD R , and HorRat values in Table 13 are summarized in Table 14 per sectors. ( 1 )  By GC/MS.— The statistical results of green tea incurred samples in Table 14 show that concerning GC/MS within- laboratory repeatability: RSD r <8% accounting for 100% illustrates that this method’s repeatability is very good in different laboratories. Between-laboratory reproducibility RSD R <25% making up 100% demonstrates that the between- laboratory reproducibility is very good. HorRat values <1.0 accounting for 100% shows that the method has achieved very good reproducibility under the corresponding analytical conditions; ( 2 )  By GC/MS/MS. —Concerning GC/MS/MS: within- laboratory repeatability RSD r <8% accounting for 100% shows that the method’s repeatability is very good in different laboratories. Between-laboratory reproducibility RSD R <25% making up 100% proves that the between- laboratory reproducibility is very good. HorRat values <1.0 accounting for 100% reveals that the method has achieved very good reproducibility under the corresponding analytical concentrations; ( 3 )  By LC/MS/MS.— Concerning LC/MS/MS: within- laboratory repeatability RSD r <15% accounting for 100% shows that the method’s repeatability is very good in different laboratories. Between-laboratory reproducibility RSD R <25% makes up 100%. ( 4 ) To summarize the discussion above, the collaborative study results show that the method efficiency is acceptable.