Plaguicidas

Journal of Chromatography A, 1015 (2003) 185–198

Multiresidue method for determination of 90 pesticides in fresh fruits and vegetables using solid-phase extraction and gas chromatography-mass spectrometry
Darinka Štajnbaher a,∗ , Lucija Zupanˇ iˇ -Kralj b cc
b a Public Health Institute, Environmental Protection Institute, Prvomajska 1, 2000 Maribor, Slovenia Department of Chemistry andChemical Technology, University of Ljubljana, Aškrˇ eva 5, 1000 Ljubljana, Slovenia c

Received 26 March 2003; received in revised form 9 July 2003; accepted 9 July 2003

Abstract A multiresidue method for analysis of 90 pesticides with different physico-chemical properties in fruits and vegetables was developed. The method involves a rapid and small-scale extraction procedure with acetone usingvortex mixing. Solid-phase extraction (SPE) on a highly cross-linked polystyrene divinylbenzene column (LiChrolut EN) was used for clean-up and pre-concentration of the pesticides from the water-diluted acetone extracts. For most fruit and vegetable samples this partial clean-up was sufficient, but some of them with more co-extracting substances need further clean-up (cereals, spinach, carrots,etc.). Diethylaminopropyl (DEA) modified silica was used for efficient removal of interferences caused by various organic acids, sugars, etc. The pesticide residues were determined by gas chromatography with a mass selective detector (GC-MS). The majority of pesticide recoveries for various fruits and vegetables were >80% in the concentration range from 0.01 to 0.50 mg/kg, except for the most polarpesticides (methamidophos, acephate, omethoate) which cannot be determined by this method. The limit of quantitation for most of the pesticides was 0.01 mg/kg with majority of relative standard deviations (R.S.D.s) below 10%. © 2003 Elsevier B.V. All rights reserved.
Keywords: Multiresidue methods; Vegetables; Fruits; Food analysis; Pesticides

1. Introduction Concern over pesticide residues infruit and vegetables has lead to the development of many multiresidue methods as the most cost-effective approach to residue
Presented at the 4th Pesticide Residue Workshop, Rome, Italy. Corresponding author. Tel.: +386-2-4500-168; fax: +386-2-4500-227. E-mail address: darinka.stajnbaher@zzv-mb.si (D. Štajnbaher).
∗

analysis. Regulatory authorities provide assurance that any pesticide remainingin or on the food is within safe limits through monitoring programmes of random sampling and analysis of raw and processed food on the market, as well as by targeting known problems. In response to this requirement, a number of methods have been developed and applied routinely for the control of pesticide residues in food [1–20]. Due to the low detection levels required by regulatory bodies and thecomplex nature of the matrices in

0021-9673/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0021-9673(03)01211-1

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D. Štajnbaher, L. Zupanˇ iˇ -Kralj / J. Chromatogr. A 1015 (2003) 185–198 cc

which the target compounds are present, efficient sample preparation and trace-level detection and identification are important aspects in an analytical method.Multiresidue method development is difficult, due to the fact that compounds of different polarities, solubilities, volatilities and pKa values have to be simultaneously extracted and analysed. Several multiresidue methods for determination of organophosphorus, organochlorine and organonitrogen pesticides in crops using gas chromatography for separation of individual compounds, followed by detectionwith selective and sensitive detectors (ECD, NPD, FPD, AED or MS) have been proposed [1–8]. Mass spectrometry is a very sensitive and selective technique for both multiresidue determination and trace-level identification of a wide range of pesticides [3,9,10,18]. A number of solvents have been used for multiresidue extractions and the most common include acetone [1,2,5–7], ethyl acetate [3,4] and...