FULLY AUTOMATED SOLID-PHASE EXTRACTION CLEANUP AND ONLINE 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 thi abendazole in various crops, Preparation of food samples involved extr action with acetone followed by solvent partitioning with dichlorometh ane-petroleum ether to draw the analytes into the organic phase. The l aborious liquid-liquid partitioning cleanup procedure described-in the literature was replaced with a fast SPE cleanup using diol-bonded sil ica cartridges, Automation of the total procedure was achieved by usin g a commercially available SPE cleanup apparatus (AS-PEC). The cleaned -up extract was injected on-line into an LC system with UV and fluores cence 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 bette r than silica-based columns in separating benzimidazole fungicides, an d different columns were compared. Results of validation studies with fortified lettuce and citrus fruit are presented. Shewhart control cha rts of analytical results of control samples demonstrated good perform ance 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 mo nitoring program in 1992-1994 are reported.