Determination of thiabendazole in potatoes, fruits, and their processed products by liquid chromatography

A liquid chromatographic method has been developed for analysis of the fungicide thiabendazole (TBZ) in fruits, potatoes, and their processed products. Extraction was performed in a 50 mL polyethylene conical centrifuge tube with a basic solution. TBZ was partitioned into methylene chloride with a polytron. No further cleanup was needed. Separation was carried out on a 5 microns Ultracarb 30 ODS column with fluorescent detection, excitation at 305 nm and emission at 345 nm. Total analysis time including extraction was 25 min per sample. Recoveries ranged from 77 to 135%. Average percent recovery for all sample types spiked from 5 ppb to 387 ppm was 94% with a coefficient of variation (CV) of 11%. Overall intra-assay CVs varied from 1.8 to 23%, and interassay CVs ranged from 1.8 to 15%. Of 194 commercial samples analyzed for TBZ, 129 were positive. TBZ in positive samples ranged from 1.1 ppb to 72.5 ppm. The limit of quantitation varied from 2.5 ppb for juices, 2.5 ppb for fruits and potatoes, and 4.5 ppb for bulk concentrates. Detection limits were 1.0 ppb for juice, fruits, and potatoes and 2 ppb for bulk concentrates. TBZ levels in the positive samples were corroborated by immunoassay.