A comparative study of three modifications of the QuEChERS method for determination of endocrine disrupting pesticide residues in lemon matrices by fast GC-MS

Three modifications of the QuEChERS (quick, easy, cheap, effective, rugged and safe) method for determination of 35 endocrine disrupting pesticides in samples with high acid content such as lemons were studied. Pesticides extraction was performed using the original QuEChERS method, citrate buffered QuEChERS method (EU version) and acetate buffered QuEChERS method (AOAC version). Final extracts were evaluated by fast gas chromatography-mass spectrometry (GC-MS) analysis. Validation experiments for all three methods were performed using a spiked pesticide free lemon matrix and matrix-matched standard solutions. Four concentration levels (1, 20, 50 and 250 μg kg−1) were tested. Recoveries from 70 to 120% with a relative standard deviation <20% were obtained for the majority of pesticides. Linearity was evaluated at a concentration range of 1–250 μg kg−1 for the buffered QuEChERS (AOAC) method with coefficients of determination (R2) higher than 0.9552 and for the original QuEChERS method with R2 higher than 0.9232. The best linearity was obtained for the citrate buffered method with R2 higher than 0.9656. The limit of detection (LOD) of the buffered QuEChERS (AOAC) method ranged between 0.1 and 18.4 μg kg−1, for the citrate buffered QuEChERS method between 0.1 and 23.6 μg kg−1 and for the original QuEChERS method between 0.1 and 14.2 μg kg−1. Results obtained by the three different QuEChERS methods were compared. The citrate buffered method is more suitable for the tested pesticides than the other two QuEChERS methods. Although the QuEChERS method is widely applied, it was shown that in difficult matrices such as lemons, the choice of modifications is analyte/matrix dependent. The three developed and validated methods were applied to the analysis of real citrus samples.