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Pang et al.:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
5, 2015
differences in test results for two parallel samples of No. 1 and
No. 2 green tea by GC/MS/MS analysis, with normal recoveries
for 20 pesticides of No. 1 sample but with no detection of
any test results for 20 pesticides of No. 2 sample. Likewise,
regarding LC/MS/MS, there are four samples fortified with
20 pesticides, of which No. 1 and No. 2 are green tea parallel
fortification samples and No. 6 and No. 7 are oolong tea
parallel samples. Recoveries for 20 pesticides of No. 1 sample
are normal, but none of the 20 pesticides has been detected in
No. 2 sample. The same is true of No. 6 and No. 7 fortification
samples, with no detection of any pesticides either, belonging to
overall deviations.
Nineteen outliers from Laboratory 18 all came from No. 6
and No. 7 oolong tea fortification samples, and the test results
from these two samples are 37% on the average compared with
those from other laboratories. As for this issue, the collaborator
has failed to find out the cause.
Seven outliers from Laboratory 27 came from the five
pesticides in No. 1 and No. 2 green tea fortification samples,
and it is judged tentatively that these pesticides were interfered
with, causing accidental errors.
To summarize the above-mentioned analysis, in the
GC/MS/MS test results, overall deviations occurred with
several specific samples for Laboratory 21 and Laboratory
18, resulting in two-thirds of the outliers concentrated in these
two laboratories. Errors from other laboratories are accident
deviations distributed in multi-kinds of pesticides.
(c)
By LC/MS/MS.—
Supplemental Tables 21–23 show
that 2957 effective data were obtained from determination of
20 pesticide residues in eight samples (excluding two blank
samples) by 24 laboratories; Grubbs and Dixon test application
was adopted, and 57 outliers were discovered (making up
1.9%). These 57 outliers came from 13 laboratories. There are
12 outliers from Laboratory 24, accounting for 21.1%; 11 from
Laboratory 28, accounting for 19.3%; nine from Laboratory 25,
making up 15.8%; and six from Laboratory 30, accounting for
10.5%. Outliers from nine other laboratories total 19, accounting
for 33.3%. Outliers from each of these nine laboratories are less
than six, caused by accidental errors.
Eleven of 12 outliers were reported by Laboratory 24 from
No. 9 and No. 10 oolong tea age samples, and the analytical
results from these two samples are 40% lower than those
from the other laboratories. There are 11 outliers reported by
Laboratory 28. These outliers came from seven pesticides in
four fortification samples (No. 1, 2, 6, and 7) of two kinds of tea.
They are mainly traced to accidental errors in the determination
of certain pesticides. There are nine outliers reported by
Laboratory 25. They came from seven pesticides in five samples
(No. 1, 2, 6, 7, and 10) traced to accidental errors with certain
pesticides. Six outliers reported by Laboratory 30 came from
green tea fortification samples No. 1 and 2, and the test results
of acetochlor, benalaxyl, bensulide, kresoxim-methyl, and
picoxystrobin in these two samples are about 40% greater than
those from other laboratories, which also belong to the category
of accidental errors with certain pesticides.
To summarize the above-mentioned descriptions, there are 57
outliers from the 2957 effective data by LC/MS/MS, accounting
for 1.9%. Fifty-seven outliers came from 13 laboratories,
Table 11. Comparison of method efficiency for determination of 20 pesticides in aged oolong tea by GC/MS/MS with and
without correction
Avg. C., μg/kg
S
r
, μg/kg
RSD
r
, %
S
R
, μg/kg
RSD
R
, %
HorRat
No.
Pesticide
No. of
labs
Without
correction
With
correction
Without
correction
With
correction
Without
correction
With
correction
Without
correction
With
correction
Without
correction
With
correction
Without
correction
With
correction
1
Trifluralin
14
325.8 386.3
19.1
19.1
5.9
4.9
113.0 112.0
34.7
29.0
1.8
1.6
2
Tefluthrin
14
154.5 195.1
8.9
8.9
5.8
4.6
48.7
47.4
31.5
24.3
1.5
1.2
3
Pyrimethanil
14
167.0 203.2
9.2
9.2
5.5
4.5
49.2
48.1
29.4
23.6
1.4
1.2
4
Propyzamide
13
192.0 216.9
10.9
10.9
5.7
5.0
42.5
41.3
22.1
19.1
1.1
0.9
5
Pirimicarb
13
179.9 220.9
9.3
9.3
5.2
4.2
46.4
44.5
25.8
20.2
1.2
1.0
6
Dimethenamid
14
72.4
89.1
3.9
3.9
5.4
4.4
20.4
19.9
28.1
22.3
1.2
1.0
7
Fenchlorphos
14
298.8 373.8
19.0
19.0
6.4
5.1
101.9 97.8
34.1
26.2
1.8
1.4
8
Tolclofos-methyl
13
169.7 204.6
8.6
8.6
5.1
4.2
45.5
44.4
26.8
21.7
1.3
1.1
9
Pirimiphos-methyl
14
163.1 200.8
15.6
15.6
9.6
7.8
53.4
51.8
32.7
25.8
1.6
1.3
10
2,4’-DDE
13
631.5 747.5
33.3
33.3
5.3
4.5
196.0 189.2
31.0
25.3
1.8
1.5
11
Bromophos-ethyl
14
155.6 191.3
9.0
9.0
5.8
4.7
47.0
44.9
30.2
23.4
1.4
1.1
12
4,4’-DDE
14
630.1 743.1
30.8
30.8
4.9
4.1
183.4 176.3
29.1
23.7
1.7
1.4
13
Procymidone
14
186.1 208.5
9.8
9.8
5.3
4.7
54.2
53.6
29.2
25.7
1.4
1.3
14
Picoxystrobin
14
373.6 425.9
19.4
19.4
5.2
4.6
85.3
82.4
22.8
19.3
1.2
1.1
15
Quinoxyfen
14
182.4 209.6
9.2
9.2
5.0
4.4
54.1
53.5
29.6
25.5
1.4
1.3
16
Chlorfenapyr
13 1511.9 1685.2 84.7
84.7
5.6
5.0
332.7 323.4
22.0
19.2
1.5
1.3
17
Benalaxyl
14
194.1 224.0
8.9
8.9
4.6
4.0
48.1
47.4
24.8
21.2
1.2
1.1
18
Bifenthrin
14
183.8 212.9
9.3
9.3
5.0
4.4
51.0
49.9
27.7
23.5
1.3
1.2
19
Diflufenican
13
191.3 216.7
11.6
11.6
6.1
5.4
41.6
40.1
21.7
18.5
1.1
0.9
20
Bromopropylate
14
387.2 438.2
22.1
22.1
5.7
5.0
84.9
82.4
21.9
18.8
1.2
1.0