Abstract
Implementation of the QuEChERS method for the routine analysis of pesticide residues – experiences and validation data
The recently developed QuEChERS multiresidue method has been successfully validated and implemented in our laboratory for routine pesticide residue analysis in produce. The method involves cryogenic processing using dry ice to minimize degradation and ensure good homogeneity and residue accessibility. Following extraction of 10 g sample with 10 mL of acetonitrile in a 40 mL centrifuge tube, 1 g NaCl and 4 g MgSO(4) are added to induce phase separation and force a wide range of pesticides to partition into the organic phase. For samples having elevated natural pH values (above 5.5) acetonitrile containing acetic acid is used to reduce losses of base sensitive pesticides. Cleanup is performed by "dispersive SPE", which entails a simple mixing of an aliquot of the acetonitrile phase with MgSO(4) and PSA (primary secondary amine) sorbent (except for the aliquot used for determining the acidic pesticides). Dried fruit and cereal samples were analysed after adding water to them. In the case of dried fruit the water was added just before cryogenic homogenisation using dry ice. Extracts containing excessive amounts of waxes of fats were additionally cleaned-up by putting them into a freezer to precipitate these impurities. Using this method, the manual work associated with sample preparation can be drastically reduced (a single analyst can prepare a batch of 8 previously chopped samples in less than 30 minutes). This has allowed us to transfer personnel from the sample preparation to the more and more expanding and demanding instrumental analysis and quality assurance areas. For validation purposes, various chopped fruit and vegetable samples have been fortified with almost 350 pesticides from different classes including N-methyl-carbamates, benzoylureas, phenylureas, benzimidazoles, phenoxyalcanoic acids, triazines, neonicotinoides, macrocyclic insecticides, azoles, triazines and organotins. Quantitative and confirmatory analysis has been performed by LC/MS-(MS) and GC/MS (EI and CI modes), using a PTV injector to inject 3 µl of the extracts. In most cases the recoveries achieved exceeded 90 % and the repeatabilities where below 5 %. The limits of detection and determination of the method meet the needs of regulatory surveillance of fruits and vegetables in almost all cases. The method has also been used for analysing the test samples of the European Proficiency Tests in 2002 (EU-PT4) and 2003 (EU-PT5) achieving excellent results.