Possibilities and Limitations of Isocratic Fast Liquid Chromatography-Tandem Mass Spectrometry Analysis of Pesticide Residues in Fruits and Vegetables
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Currently, state-of-the-art analytical methods for multiclass, multiresidue monitoring of pesticides in foods use ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) for analysis of LC-amenable analytes. UHPLC-MS/MS for > 100 pesticides typically takes 10 min per injection using gradient elution in the reversed-phase mode, plus typically 3–5 min for re-equilibration between injections. Isocratic mobile-phase conditions eliminate need for the re-equilibration, and can greatly speed analysis time. In this study, fast isocratic LC-MS/MS was evaluated using a C18 analytical column of 3 cm × 4.6 mm i.d. with 3 µm particles and a mobile phase consisting of 10 mM ammonium formate at pH 3 in 47.5/47.5/5 (v/v/v) acetonitrile/methanol/water. Flow rate was 0.4 mL/min and injection volume was 50 µL. Sample preparation entailed a formate-buffered QuEChERS method for fruit and vegetable samples, typically yielding extract of 1.27 g/mL sample equivalent in 94/6 acetonitrile/water without additional cleanup. The analysis time was 2.6 min covering 88 diverse pesticide analytes each with three ion transitions (dwell times of 5 ms and 5 ms interscan delays). Validation experiments involving fortification of water, pear, tomato, cucumber, eggplant, and cilantro at 10 and 100 ng/g (n = 10 for each matrix and level) showed that the method achieved acceptable quantification with 70–120% recoveries and ≤ 25% RSD for 32–62 (36–70%) of the analytes depending on the matrix. Using regulatory identification criteria, only 6 false positives occurred above 10 ng/g among 4400 analyte/matrix/sample combinations, but false negatives varied depending on the pesticide/matrix pair, with results improving significantly for analytes with retention times > 1.3 min. This study demonstrated the feasibility and limits of isocratic LC-MS/MS for rapid screening of common commodities monitored for pesticide residues.
KeywordsIsocratic liquid chromatography-tandem mass spectrometry (LC-MS/MS) High-throughput analysis QuEChERS sample preparation Qualitative identification Pesticide residues Fruits and vegetables
The author thanks Robyn Moten for technical assistance in the laboratory and Gary Strahan for NMR analysis of the extracts to determine water content.
Mention of brand or firm names does not constitute an endorsement by the U.S. Department of Agriculture above others of a similar nature not mentioned.
Compliance with Ethical Standards
Conflict of interest
The author declares no conflict of interest.
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