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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.
(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
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:
Table 1. Pesticides selected for the collaborative study
GC/MS and GC/MS/MS
LC/MS/MS
No.
Pesticide
MRL, μg/kg
Source
Pesticide
MRL, μg/kg
Source
1
2,4
'
-DDE
200
EU
Acetochlor
10
EU
2
4,4
'
-DDE
200
EU
Benalaxyl
100
EU
3
Benalaxyl
100
EU
Bensulide
30
Japan
4
Bifenthrin
5000
EU
Butralin
20
EU
5
Bromophos-ethyl
100
EU
Chlorpyrifos
100
EU
6
Bromopropylate
100
EU
Clomazone
20
EU
7
Chlorfenapyr
50000
EU
Diazinon
20
EU
8
Diflufenican
50
EU
Ethoprophos
20
EU
9
Dimethenamid
20
EU
Flutolanil
50
EU
10
Fenchlorphos
100
EU
Imidacloprid
50
EU
11
Picoxystrobin
100
EU
Indoxacarb
50
EU
12
Pirimicarb
50
EU
Kresoxim-methyl
100
EU
13
Pirimiphos-methyl
50
EU
Monolinuron
50
EU
14
Procymidone
100
EU
Picoxystrobin
100
EU
15
Propyzamide
50
EU
Pirimiphos methyl
50
EU
16
Pyrimethanil
100
EU
Propoxur
100
EU
17
Quinoxyfen
50
EU
Quinoxyfen
50
EU
18
Tefluthrin
50
EU
Tebufenpyrad
100
EU
19
Tolclofos-methyl
100
EU
Triadimefon
200
EU
20
Trifluralin
100
EU
Trifloxystrobin
50
EU