Submitted to: Chromatographia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2018
Publication Date: 8/25/2018
Citation: Lehotay, S.J. 2018. Possibilities and limitations of isocratic fast liquid chromatography-tandem mass spectrometry analysis of pesticide residues in fruits and vegetables. Chromatographia. 82:235-250. https://doi.org/10.1007/s10337-018-3595-0.
Interpretive Summary: Analysis of pesticide residues in fruits and vegetables is an important application for improved food safety and fair trade practices, and regulatory monitoring is routinely conducted in countless laboratories worldwide. As described in a Government Accountability Office report on food safety (GAO-15-38), higher sample throughput is needed to improve monitoring programs of imported and domestic foods. This study was devised to address that need by demonstrating the limits and feasibility of 5-fold faster chromatographic separations than done currently. The faster approach worked well for many pesticides, but not all, and several ways to make improvements were pinpointed for future studies. The work is especially useful to regulatory agencies, agrochemical companies, and contract monitoring labs, and it is a step in the right direction for higher-throughput pesticide residue monitoring to better meet food safety needs.
Technical Abstract: 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 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 and a mobile phase consisting of 47.5/47.5/5 acetonitrile/methanol/water. 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 3 ion transition 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.