Simultaneous detection of agricultural antibiotics via high-throughput LC-MS/MS: residue survey in plant-based foods

A high-throughput LC-MS/MS method was developed for the simultaneous quantification of six antibiotics - streptomycin, dihydrostreptomycin, kasugamycin, validamycin, oxolinic acid, and oxytetracycline in plant-derived foods. These antibiotics, used as agricultural pesticides, were extracted using McIlvaine buffer (pH 7) and purified via dual solid-phase extraction with InertSep WCX and GC cartridges. Chromatographic separation was achieved with a column manager system, enabling dual-mode analysis from a single vial using a Xevo TQ-XS/I-Class Plus UPLC system. The method achieved LOQs of 10 ng/g for all analytes, with recovery of 88.2-111.7% and repeatability below 11% for grapefruit, and recovery of 94.3-115.7% and repeatability below 21% for cabbage, all meeting Japanese method validation performance criteria. The developed method was applied to 112 fruit and vegetable samples collected from Tokyo markets. Seven samples contained detectable residues, with four exceeding the limits of quantification. Oxolinic acid was the most frequently detected antibiotic, reaching up to 165 ng/g. This represents the first report of oxolinic acid residues in plant-derived foods. Our findings highlight the need for ongoing monitoring of antibiotic residues in plant-based foods. Our method provides a practical analytical tool to support food safety risk assessments and antimicrobial resistance monitoring.