Rapid simultaneous screening and identification of multiple pesticide residues in vegetables

A method for the rapid simultaneous screening and identification of multiple pesticide residues in vegetables was established using a novel database and gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry (GC-QTOF MS). A total of 187 pesticides with different chemical species were measured by GC-QTOF MS to create the database, which collected the retention time and exact masses of ions from the first-stage mass spectrum (MS1 spectrum) and second-stage mass spectrum (MS2 spectrum) for each pesticide. The workflow of the created database consisted of MS1 screening for possible pesticides by chemical formula match and MS2 identification for structural confirmation of product ion by accurate mass measurement. To evaluate the applicability of the database, a spinach matrix was prepared by solid phase extraction, spiked with a mixture of 50 pesticides at seven concentrations between 0.1 and 10 ppb, and analyzed by GC-QTOF MS. It was found that all of the 50 pesticides with concentrations as low as 5 ppb were detected in the MS1 screening step and accurate masses were identified with errors less than 2.5 mDa in the MS2 identification step, indicating high sensitivity, accuracy, selectivity and specificity. Finally, to validate the applicability, the new method was applied to four fresh celery, rape, scallion and spinach vegetables from a local market. As a result, a total of 13 pesticides were found, with 11 in celery, 9 in rape, 3 in scallion and 2 in spinach. In conclusion, GC-QTOF MS combined with an exact mass database is one of the most efficient tools for the analysis of pesticide residues in vegetables. (C) 2012 Elsevier B.V. All rights reserved.