The Impact of Pesticides - Academy Publish

ecoveries (>70%) for certain pH-dependent pesticides (e.g. pymetrozine, imazalil,thiabendazole) independent of the fruit/vegetable matrix (Lehotay et al., 2005b).Lehotay et al. (2005b) modified the method to use relatively strong acetate bufferingconditions and Anastassiades et al. (2007) chose to use weaker citrate bufferingconditions in terms of ionic strength. Both versions of these methods went throughextensive interlaboratory program (Lehotay et al., 2007) for dozens of pesticides atfortified and incurred at different levels in different matrices and using differenttypes of GC–MS and LC–MS/MS conditions and instruments. Both methodssuccessfully met statistical criteria for acceptability from independent scientificstandards organizations, with the acetate-buffering version becoming AOACOfficial Method 2007.01 (AOAC, 2007) and the citrate-buffering version beingnamed European Committee for Standardization (CEN) Standard Method EN 15662(CEN, 2008).The QuEChERS approach is very flexible and it serves as a template formodification depending on the analyte properties, matrix composition, equipmentand analytical technique available in the laboratory. The template is also veryrugged in that high recoveries will be achieved for many pesticides in manymatrices even if different ratios and types of sample size, solvent, salts and sorbentsare used in modifications. The ruggedness characteristics of the QuEChERSapproach have been thoroughly evaluated in the original (Anastassiades et al., 2003)and subsequent publications (Lehotay et al., 2010; Stubbings and Bigwood, 2009;Aguilera-Luiz et al., 2008; Cunha et al., 2007; Díez et al., 2006; Lehotay et al.,2005c). In multiclass, multiresidue pesticide analysis, the sample preparationmethod inherently necessitates broad analytical scope which makes it impossible toobtain a high degree of clean-up without reducing recoveries for some pesticides.However, greater clean-up can be achieved by using different sorbents in d-SPE ifthe application has reduced analytical scope (Li et al., 2011; Koesukwiwat et al.,2010; Wong et al., 2010).Sample preparation is always the major bottleneck in any analytical procedure forthe determination of chemical residues in food products (Díez et al., 2006). Since2003 many papers have been published where QuEChERS or related methods aresuccessfully applied for foods of animal origin. A modified QuEChERS extractionmethod was developed and validated to detect 38 compounds (benzimidazoles,avermectins and flukicides) in milk samples by UHPLC-MS/MS. The compoundsresidues were extracted into acetonitrile using magnesium sulphate and sodiumchloride to induce liquid–liquid partitioning followed by d-SPE clean-up. Theextract was concentrated into dimethyl sulphoxide, which was used as a keeper toensure analytes remain in solution. Using rapid polarity switching in electrosprayionisation, a single injection was capable of detecting both positively and negativelycharged ions in a 13min run time. The method was validated at two levels: theunapproved use level and at the maximum residue level (MRL). The decision limit(CCα) of the method was in the range of 0.14–1.9 and 11–123 µg kg −1 for drugsvalidated at unapproved and MRL levels, respectively. The performance of themethod was successfully verified for benzimidazoles and levamisole byparticipating in a proficiency study (Whelan et al., 2010).AcademyPublish.org - The Impact of Pesticides358