Page 30 - Volume 2,Issue 2, July 2009

Anagnostopoulos

et al.

76

methods, based on acetone, was the modi-

fied Luke method [acetone followed by par-

titioning with a mixture of dichloromethane

(DCM) and light petroleum] (16). Luke

et al

.

(9) developed a multiresidue method that

included not only organochlorine but also

organophosphorus compounds. According

to this method, samples of fruit and vege-

tables (200 gr) were extracted with 200 ml

of acetone and the extracts were then par-

titioned into dichloromethane/petroleum

ether mixed solvent (50:50 v/v) by a Florisil

clean-up step similar to that used by Mills

et al

. (12). Luke

et al.

(10) improved this pro-

cedure by eliminating the Florisil clean-up

step and adding petroleum ether follow-

ing the initial concentration to remove trac-

es of DCM. Specht and Tilkes (14) published

their multiresidue method for 90 pesticides

in samples of both vegetable and animal or-

igins. They also untilled DCM to partition the

pesticides from aqueous acetone extracts,

but added a gel permeation chromatogra-

phy (GPC) clean-up step.

Chromatographic techniques, main-

ly gas chromatography (GC) and high-per-

formance liquid chromatography (LC), have

usually been applied for the determination

of pesticide residues in food samples (7).

Liquid chromatography-mass spectrometry

(LC–MS) allows the rapid and efficient de-

termination of many compounds (6). It has

become a powerful tool for pesticide resi-

due analysis in a variety of complex matri-

ces, due to its inherent advantages: selec-

tivity and sensitivity are notably improved,

the sample pre-treatment steps can be min-

imized and reliable quantification and con-

firmation can be easily achieved at the low

concentration levels required. Many publi-

cations on pesticide residue analysis using

this technique were dated from the early

2000s (2, 4, 8).

Analytical methodologies employed

must be capable of measuring residues at

very low levels and must also provide unam-

biguous evidence to confirm both the iden-

tity and the concentration of any residue

detected. Within-laboratory method vali-

dation should be performed to provide ev-

idence that a method is fit for the purpose

for which it is to be used. Method validation

is a requirement of accreditation bodies and

must be supported and extended by meth-

od performance verification during routine

analysis (analytical quality control and on-

going method validation). All procedures

(steps) that are undertaken in a method

should be validated, if practicable (5).

The purpose of this paper is to pres-

ent the validation of a rapid multiresidue

method by liquid chromatography-tan-

dem mass spectrometry (LC-MS/MS) with

electron spray interface (ESI), using an ex-

traction method based on acetone–dichlo-

romethane–petroleum ether for the deter-

mination of various pesticides fromdifferent

chemical classes in fruit and vegetables of

high water content. The procedure has been

applied for the screening, confirmation and

quantification of 56 representative multi-

class pesticides in peaches, a representa-

tive commodity of fruit and vegetables of

the high water content category (5) and was

extended to the analysis of 14 samples of

stone fruit taken from the market.

Materials and methods

1. Chemicals and reagents

In the present work, 56 analytes were se-

lected with distinct physicochemical char-

acteristics, as shown in Table 1. They includ-

ed polar and non-polar compounds, as well

as compounds of various molecular mass-

es. The selected analytes belong to different

chemical classes: anilinopyrimidine, ben-

zimidazole, carbamate, N-methyl carbam-

ate, oxime carbamate, chloroacetamide, cin-

namic acid, diacylhydrazine, hydroxyanilide,

imidazole, morpholine, neonicotinoid, or-

ganophosphorous, oxadiazine, pyrazole,

pyridinecarboxamide, quinoline, strobilurin,

tetrazine and triazole pesticides.

The following pesticide active ingredi-

ents, obtained from Dr Ehrenstorfer Labo-

ratories GmbH (Germany), were used in the

present study: acetamiprid, alachlor, aldi-

carb, aldicarb sulfone, aldicarb sulfoxide,