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cleanup using dSPE, highly complex matrices
will benefit from more exhaustive sample
cleanup techniques, such as cartridge SPE [2].
Incurred residues were also determined and
the number of pesticides detected by each
technique was comparable. However, there
were some pesticides for which residue con-
centration could only be reported by either
GCxGC-TOFMS or LC-MS/MS.
Conclusions
Use of both GCxGC-TOFMS and LC-MS/MS
provides more comprehensive results for
pesticide residue monitoring in food. The
QuEChERS sample preparation approach
using Restek Q-sep™ extraction salts and dSPE
cleanup tubes worked well for a variety of
Figure 1: GCxGC-TOFMS contour plots for grape and lemon QuEChERS extracts. The
lemon extract is much more complex than the grape extract and could not be analyzed
by one-dimensional GC.
Columns:Rxi®-5Sil MS, 30 m, 0.25 mm ID, 0.25 µm (cat.# 13623) and Rtx®-200, 1.5 m, 0.18 mm ID, 0.20 µm (cat.# 45001);Samples: Grape
and lemon samples were fortified at 10 ng/g with a mixed pesticide standard solution. Snap-and-shoot internal standards (cat.# 33267 and
33261) containing the compounds specified in the EN15662 QuEChERS method were added. Samples were extracted with Q-sep™ European
method extraction salts (cat.# 26236) and extracts were then cleaned with QuEChERS dSPE cleanup tubes (cat.#26230). For complete sample
preparation details and analytical conditions, visit and enter chromatograms GC_FF1217 and GC_FF1218 in the search.
A: Grape
B: Lemon
pesticides and commodities. In general, good
recoveries were achieved as determined by
both GCxGC-TOFMS and LC-MS/MS. However,
more difficult matrices like lemon may benefit
from additional cleanup of sample extracts.
For the complete technical article, visit
Acknowledgements
U.S. Food and Drug Administration/Center for Food
Safety and Applied Nutrition; LECO Corporation
References
[1] M. Anastassiades, S.J. Lehotay, D. Stajnbaher, F.J.
Schenck, J. AOAC International 86 (2003) 412.
[2] J. Cochran, J. Thomas, J. Kowalski, M. Misselwitz, R.
Lake, Determining Pesticides in Dietary Supplements
with QuEChERS Extraction, Cartridge SPE, and
GCxGC-TOFMS, GNAN1338, Restek Corporation, 2011.
Pesticide
Black Grapes Lemon
GCxGC LC GCxGC LC
Propoxur 92 110 INT 75
Methamidophos 170 73 79 66
Acephate 73 NA 88 NA
Propham 100 50 130 ND
1-Naphthol 95 NA 110 NA
o-Phenylphenol 91 NA 100 NA
Tebuthiuron 92 90 110 42
Omethoate 68 98 100 89
Dimethoate 93 91 100 79
Prometon 96 73 110 47
Terbacil 110 NA INT NA
Pirimicarb 98 NA 100 NA
Metribuzin 110 76 110 58
Fuberidazole 96 85 98 ND
Carbaryl 120 150 72 14
Metalaxyl 93 81 95 52
Terbutryn 100 79 99 4
Ethofumesate 110 120 81 19
Benthiocarb 85 NA 110 NA
Cyprodinil 99 86 91 ND
Thiabendazole 110 70 83 ND
Furalaxyl 130 85 110 37
Triadimenol 110 NA 100 NA
Siduron 98 96 120 35
Imazalil NA 70 XXX XXX
Fludioxonil 120 NA 96 NA
Myclobutanil 130 110 100 13
Buprofezin XXX XXX 94 24
Oxadixyl 120 90 97 40
Mepronil 120 91 100 ND
Carfentrazoneethyl 110 150 110 74
Fenhexamid 120 51 87 ND
Propargite 110 130 100 ND
Piperonylbutoxide 110 95 110 ND
Pyriproxyfen 96 100 99 ND
Fenarimol 89 NA 100 NA
Bitertanol 92 NA 110 NA
Prochloraz 78 80 100 ND
Pyraclostrobin 110 92 61 ND
Azoxystrobin 98 86 110 30
Dimethomorph 90 98 97 25
Table I: Percent recovery values for 10 ng/g
fortified samples prepared using QuEChERS
and analyzed by GCxGC-TOFMS and LC-MS/MS.
Restek Recommends
Comprehensive solutions:
Q-sep™ QuEChERS Sample Prep Products
GCxGC Columns and Resources
Ultra Aqueous C18 LC Columns
Certified Reference Materials
GC_FF1217
GC_FF1218
XXX = incurred pesticides NA = not analyzed
ND = not detected INT = affected by interferences