Fully automated solid-phase extraction cleanup and on-line liquid chromatographic determination of benzimidazole fungicides in fruit and vegetables

A liquid chromatographic (LC) method using fully automated solid-phase extraction (SPE) sample cleanup and on-line LC analysis was developed for determination of the benzimidazole fungicides carbendazim and thiabendazole in various crops, Preparation of food samples involved extraction with acetone followed by solvent partitioning with dichloromethane-petroleum ether to draw the analytes into the organic phase. The laborious liquid-liquid partitioning cleanup procedure described-in the literature was replaced with a fast SPE cleanup using diol-bonded silica cartridges, Automation of the total procedure was achieved by using a commercially available SPE cleanup apparatus (AS-PEC). The cleaned-up extract was injected on-line into an LC system with UV and fluorescence detection in tandem, Chromatographic separations were performed with a methanol-phosphate buffer mobile phase (pH = 7), and different polymeric stationary phases. The polymer-based columns performed better than silica-based columns in separating benzimidazole fungicides, and different columns were compared. Results of validation studies with fortified lettuce and citrus fruit are presented. Shewhart control charts of analytical results of control samples demonstrated good performance of the complete system. Sample throughput (extraction, automated SPE, and on-line LC analysis) was about 50 samples per 24 h. Residues of carbendazim and thiabendazole found during our pesticide residue monitoring program in 1992-1994 are reported.