Routine approach to qualitatively screening 300 pesticides and quantification of those frequently detected in fruit...

This paper describes an efficient and effective analytical scheme to first screen for 300 pesticides in fruit and vegetables samples using liquid chromatography tandem mass spectrometry (LC-MS/MS) with a commercially enhanced product ion method. Then presumed positive extracts are analysed using a quantitative and confirmatory LC-MS/MS method optimized for 55 pesticides. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) method with acetate buffering (AOAC Official Method 2007.01) was used for sample preparation, which has been previously shown to yield high-quality results for hundreds of pesticide residues in foods. The advantages and disadvantages of both the qualitative screening and quantitative/confirmatory methods and their combination are critically discussed. No false-negatives for the 55 pesticides occurred above 10 ng g(-1) for extracts analysed by both LC-MS/MS methods, and the no false-positives were encountered from the screening analysis (after analyst review) because all presumptive identifications were confirmed in the second analysis. The monitoring scheme was applied during a one-year period on 200 fruit and vegetable samples from Hungarian markets. No pesticide residues were found in half the samples, and twelve violations of European maximum residue limits were detected.