Page 41 - Volume 3, Issue 2, July 2010

© Benaki Phytopathological Institute
Anagnostopoulos et al. 72
ities (wheat, rice, oats, cereals, etc.). Schenck
et al . (14) used 65% acetonitrile in water as
extraction solvent. The extracts were salted
out with NaCl and MgSO 4 and cleaned-up
on a series of graphitized carbon black and
amino SPE cartridges before analysis of 33
pesticides in grain. Wang et al. (16) used ac-
etonitrile and hexane as extraction solvents
and clean-up with SPE cartridges for the de-
termination of 13 pesticides in soy-based in-
fant formula using LC-MS/MS. Lehotay et al.
(2, 9, 10) conducted a study to establish a
miniaturized acetonitrile-based extraction,
followed by a dispersive solid phase extrac-
tion clean-up step (QuEChERS). Walorczyk
(15) used the QuEChERS method for the de-
termination of 122 GC amenable pesticides
in cereals and animal feed. Payá et al. (12)
validated the QuEChERS method for 38 GC
amendable pesticides in wheat flour using
GC-MS/MS and 42 LC amendable pesticides
using LC-MS/MS.
In the last few years, modern analytical
techniques, such as GC-MS/MS, LC-MS/MS,
LC-TOF/MS, are used for the detection of
pesticides in baby foods. These techniques
require expensive and sophisticated equip-
ment, increasing the initial purchase cost
to the laboratory as well as that of the an-
alytical processes themselves. In addition,
the number of accredited laboratories in
some EU-bordering countries is still low and
the legislation and organization of agricul-
tural plant production in these countries
have not reached yet the required level (13).
Therefore, the methods used for the analy-
sis of baby food samples or the relevant ag-
ricultural products need to be simple, fast,
low-cost, and sensitive. They also need to
be suitable for routine analysis in a variety
of laboratories and harmonized with the EU
legislation requirements concerning the val-
idation criteria, so as to ensure the quality
and comparability of analytical results (5).
The aim of this paper was to validate a
multiresidue analytical method suitable for
the simultaneous extraction and determina-
tion of 25 priority pesticides in cereal-based
baby food samples by using gas chromatog-
raphy with two different detectors, an elec-
tron capture and a nitrogen phosphorus de-
tector.
Materials and Methods
Reagents and chemicals
In this work, the following 25 priority
pesticides and metabolites, obtained from
Dr Ehrenstorfer Laboratories (GmbH Ger-
many) and included in the European Union
Directives 2006/125/EC and 2006/141/ EC
were studied (4): aldrin, cadusafos, deme-
ton-s-methyl, demeton-s-methyl sulfone,
demeton-s-methyl sulfoxide, dieldrin, dime-
thoate, disulfoton, disulfoton-sulfone, disul-
foton-sulfoxide,ethoprophos,fensulfothion,
fensulfothion sulfone, fensulfothion-oxon,
fensulfothion-oxon-sulfone, terbufos, ter-
bufos-sulfone, terbufos-sulfoxide, fipronil,
fipronil-desulfinyl, heptachlor, heptachlo-
repoxid (trans), hexachlorobenzene, nitro-
fen, omethoate. LC-MS grade acetonitrile,
2,2,4-trimethyl pentane and toluene pesti-
cide residue analysis grade were used. Mag-
nesium sulphate anhydrous, disodium hy-
drogencitrate sequihydrate were obtained
from Fluka (Buchs, Switzerland). Sodium
chloride (ACS reagent grade ≥99.0%) and
trisodium citrate dihydrate were obtained
from Sigma-Aldrich (Madrid, Spain). PSA
(Primary Secondary Amine) sorbent Bonde-
sil-PSA 40μm was obtained from Varian.
Stock and working standard solutions
Stock standard solutions at 1000 mg/l
were prepared in acetone for each pesti-
cide and stored at -20 oC. Standard mixture
solutions of the compounds were prepared
in 2,2,4-trimethylpentane/toluene (90/10) at
intermediate concentrations (1-10 mg/l) and
stored at -20 oC. In order to acquire the reten-
tion time of each analyte, working solutions
containing only one analyte at 0.5 mg/l
were prepared and injected to the chro-
matographic system.
Working standard mixture solutions for
calibration were prepared in wheat flour ex-
tract, previously analysed for the absence of
compounds interfering with the analytes.