ABSTRACT
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.
