AOAC RI Chemical Cont. Methods-2018 Awards

1430 Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015 contaminants. So, for this collaborative study an expert review panel within the AOAC Method-Centric Committee on Pesticide Residues recommended a study protocol based on 20 representative compounds that can be analyzed by GC/MS and GC/MS/MS and 20 compounds that can be analyzed by LC/MS/MS and applied to two teas for an interlaboratory validation of this method in a collaborative study. The 40 pesticides recommended by the expert panel out of the 653 pesticides for this multilaboratory validation study showing their EU MRLs are listed in Table 1.

provided each collaborating laboratory with instructions on how to conduct the proficiency recovery test and at least five portions of 5 g blank green tea and oolong tea samples. Figure 1 is a flow chart of the validation plan that was conducted for the collaborative study.

Quality Assurance

(a)  Precollaborative study requirements .—Prior to the determination of the collaborative samples, collaborators should practice testing the samples in advance in their own laboratories. No collaborator shall undertake the analysis of the official collaborative samples until the Study Director has determined that satisfactory performance has been achieved for the precollaborative test samples. [ Note : Results from any laboratories that conduct the collaborative study without evidence of confirmation of proficiency status by the Study Director through a precollaborative sample analysis shall be automatically excluded from the analysis and interpretation of the collaborative study data.] ( 1 )  Precollaborative study experiments.— Collaborators conducted fortified recovery replicate tests with blank tea samples (green tea or oolong tea) and the mixed pesticide working standard solutions supplied by the Study Director. To each 5 g blank tea sample add 50 μL mixed pesticide working standard solutions and conduct at least five replicate analyses. Calculate the analytical recovery, the RSD (for n = 5), the ion abundance ratio, and the linear coefficient of determination (R 2 ) for the calibration curve and submit to the Study Director. ( 2 )  Precollaborative study qualification and acceptance criteria.— To demonstrate proficiency in the use of the method, laboratory results must satisfy the following acceptance criteria:

(b)  Concentration ranges for the analytes to be considered in the study. —The concentration range selected for the 40 target pesticides is 10–2000 μg/kg based on guidance provided by an expert panel at two meetings organized by the AOAC Pesticide and Chemical Contaminants Method-Centric Community. One was at the Florida Pesticide Residue Workshop held July 18–21, 2011, and the other was the 125th AOAC Annual Meeting held in New Orleans, LA in September 2011. (c)  Fortified and blank tea samples to be analyzed for the collaborative study. —Every collaborator was expected to analyze four fortified samples (Samples No. 01 to No. 02 for green tea; No. 06 to No. 07 for oolong tea); and two blank samples. (d)  Incurred samples for the collaborative study. —Three incurred samples (No. 03 to No. 05 for green tea; No. 08 to No. 10 for oolong tea) generated from a tea plantation named “Youshan Garden” in Fujian, where growing teas were sprayed with pesticides as per the relevant commercial procedure, picked at different phases of cultivation, dried, and then processed were tested as incurred samples. (e)  Samples for precollaborative study. —To demonstrate proficiency at each participating laboratory, the Study Director

Table 1. Pesticides selected for the collaborative study GC/MS and GC/MS/MS

LC/MS/MS

No.

Pesticide 2,4 ' -DDE 4,4 ' -DDE Benalaxyl Bifenthrin

MRL, μg/kg

Source

Pesticide

MRL, μg/kg

Source

1 2 3 4 5 6 7 8 9

200 200 100

EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU

Acetochlor Benalaxyl Bensulide

10

EU EU

100

30 20

Japan

5000

Butralin

EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU EU

Bromophos-ethyl Bromopropylate Chlorfenapyr Diflufenican Dimethenamid Fenchlorphos Picoxystrobin

100 100

Chlorpyrifos Clomazone

100

20 20 20 50 50 50

50000

Diazinon

50 20

Ethoprophos

Flutolanil

10 11 12 13 14 15 16 17 18 19 20

100 100

Imidacloprid Indoxacarb

Pirimicarb

50 50

Kresoxim-methyl

100

Pirimiphos-methyl

Monolinuron Picoxystrobin

50

Procymidone Propyzamide Pyrimethanil Quinoxyfen

100

100

50

Pirimiphos methyl

50

100

Propoxur

100

50 50

Quinoxyfen Tebufenpyrad Triadimefon Trifloxystrobin

50

Tefluthrin

100 200

Tolclofos-methyl

100 100

Trifluralin

50