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Pang et al.:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
5, 2015
Statistical analysis withAOAC software also proves that method
efficiencies for GC/MS, GC/MS/MS, and LC/MS/MS were
acceptable (
1
) for green tea 20 pesticide fortification samples
by the three methods: GC/MS: Avg. C.: 37.5–759.6 μg/kg,
Avg. Rec. 87.7–96.0%, RSD
r
: 2.1–4.9%, RSD
R
: 6.5–9.9%,
HorRat: 0.3–0.5; GC/MS/MS: Avg. C.: 37.5–749.1 μg/kg,
Avg. Rec. 87.0–97.1%, RSD
r
: 3.1–6.0%, RSD
R
: 6.6–14.8%,
HorRat: 0.3–0.7; LC/MS/MS: Avg. C.: 18.2–191.8 μg/kg,
Avg. Rec. 91.3–97.7%, RSD
r
: 4.9–9.4%, RSD
R
: 8.4–17.1%,
and HorRat: 0.3–0.7; (
2
) for oolong tea 20 pesticide
fortification samples by the three methods: GC/MS: Avg. C.:
17.3–335.7 μg/kg, Avg. Rec. 81.0–91.1%, RSD
r
: 2.8–7.8%,
RSD
R
: 12.5–25.0%, HorRat: 0.5–1.3; GC/MS/MS: Avg. C.:
17.5–335.8 μg/kg, Avg. Rec. 77.1–90.8%, RSD
r
: 1.4–5.4%,
RSD
R
: 7.0–32.7%, HorRat: 0.4–1.3; LC/MS/MS: Avg. C.:
8.5–84.3 μg/kg, Avg. Rec. 82.5–93.7%, RSD
r
: 3.6–10.2%,
RSD
R
: 13.6–29.7%, and HorRat: 0.4–1.3; (
3
) for oolong tea 20
pesticide aged samples by the three methods: GC/MS: Avg. C.:
77.6–1642.6 μg/kg, RSD
r
: 2.0–5.8%, RSD
R
: 8.9–16.9%,
HorRat: 0.4–0.9; GC/MS/MS: Avg. C.: 72.4–1511.9 μg/kg,
RSD
r
: 4.6–9.6%, RSD
R
: 21.7–34.7%, HorRat: 1.1–1.8;
LC/MS/MS:Avg. C.: 34.2–441.6 μg/kg, RSD
r
: 5.0–9.1%, RSD
R
:
16.8–34.6%, and HorRat: 0.7–1.6; (
4
) for green tea five
pesticide incurred samples by the three methods: GC/MS
(pyrimethanil and bifenthrin): Avg. C.: 613.3 and 77.8 μg/kg,
RSD
r
: 3.3 and 4.0%, RSD
R
: 12.2 and 23.0%, HorRat: 0.7 and
1.0; GC/MS/MS (pyrimethanil and bifenthrin): Avg. C.: 575.4
and 78.6 μg/kg, RSD
r
: 5.6 and 5.6%, RSD
R
: 14.1 and 22.2%,
HorRat: 0.8 and 0.9; LC/MS/MS (acetochlor, triadimefon, and
trifloxystrobin): Avg. C.: 14.1–90.7 μg/kg, RSD
r
: 8.4–10.6%,
RSD
R
: 21.3–23.6%, HorRat: 0.8–0.9. To sum up the above-
mentioned data analysis, Avg. C., Avg. Rec., RSD
r
, RSD
R
, and
HorRat values all met AOAC technical requirements except for
specific data. The Study Director recommends this method as
Official First Action.
Second, one important experience achieved in this
collaborative study is that a pre-study stage must be added in
designing the collaborative study protocol for a complex topic.
Tea matrixes are relatively complicated, with a certain difficulty
for using three techniques for determination of hundreds of
pesticide residues. The Study Director very much appreciated Jo
Marie Cook (Florida Department of Agriculture and Consumer
Services, Bureau of Chemical ResidueLaboratories, Tallahassee,
Florida Department of Agriculture and Consumer Services,
Bureau of Chemical Residue Laboratories, Tallahassee, FL) for
her suggestion of adding a pre-study stage in the collaborative
study protocol that was first proposed in 2010. Therefore, the
protocol stipulated that the four indexes of recoveries, RSD, R
2
,
and ion abundance with target pesticides in the pre-study would
have to meet the acceptance criteria, otherwise collaborators
would, in principle, forfeit their right to continue analysis of
official collaborative study samples. An expert once wrote to
the Study Director during the collaborative study period: “If we
understood well the final amount is five grams. It means only
one testing opportunity, just one shot. We consider important to
get some more material (e.g., 10 g) for duplicate analysis. Is it
possible?” The Study Director replied: “What you comprehend
is absolutely correct. For the official collaborative study, there
is only one sample for one preparation, which is what you called
“just one shot.” However, we have provided you with sufficient
practice samples and request the collaborators to practice
strictly in the first place. Only after they meet the acceptance
criteria can they start the official collaborative study. If your
practice results have met with the criteria, I believe that you
will be able to achieve very good collaborative study results
with only one shot.” Now the study has finally achieved the
triumphant results of “one sample good only for one shot.” The
reason for it is that the pre-study played a vital role in it, which
is an important experience for success.
Third, there is a lesson that we should learn, which is that
several laboratories used a Waters LC/MS/MS instrument in
this collaborative study, and the transitions of a target pesticide
were recommended by other colleagues because in the Study
Director’s laboratory such an instrument is unavailable, and he
did not verify the transitions, with the result that mistakes and
loss were caused for the collaborators owing to our supplying
the incorrect ion information for several laboratories. This
reflects the Study Director’s negligence in his work, which is
an important lesson to learn, and here the Study Director also
extends his deep apology to the collaborators involved.
All in all, this is a very complicated and important systematic
project, which is unforgettable for all the experts involved
with the collaborative study, especially those who directly
participated in the study. The Study Director considers AOAC
interlaboratory collaborative study is a great undertaking and
hopes that more and more analytical chemists will be involved
in it, making greater contributions for the development of
AOAC
Official Methods
.
Note
: Annex 1: Supporting Documents (such as specifications
of instruments and SPE cartridges, determination results,
statistical results, etc.), Annex 2: The SLV AOAC OMA-2011-
Jan-001, and Annex 3: Tea Hydration Method are available on
the
J. AOAC Int.
website.
Acknowledgments
The Study Director thanks the members of the Methods
Committee on Pesticides for their advice and guidance in
the protocol design and review of the study, as well as the
following organizations and individuals who participated in the
collaborative study:
Renzo Boni, Conserve Italia, Italy
Zong-Mao Chen, Feng-Jian Luo, Chinese Academy of
Agricultural Sciences (CAAS), P.R. China
Asish Chakraborty, SGS India Private Ltd, India
Amadeo R. Fernandez, Ana Lozano, EURL-FV, University
of Almería, Spain
Qi-Lei Guo, National Food Quality & Safety Supervision and
Inspection Center, P.R. China
Guk-Tak Han, Yu-Ri Lee, Ministry for Food, Agriculture,
Forestry and Fisheries, National Agricultural Products Quality
Management Service Chungnam Province, Republic of Korea
Vincent Hanot, Scientific Institute of Public Health (IPH),
Belgium
Shan-Mei Huang, Central Chemical Laboratory of SGS-
CSTC Standards Technical Services Co., Ltd, Guangzhou
Branch, P.R. China
Yu-Ju Huang, Tunding Substation, Tea Research and
Extension Station, Taiwan, P.R. China
Naoki Kanamaru, Japan Grain InspectionAssociation Central
Research Laboratory, Japan