Simultaneous direct analysis of benzimidazole fungicides and relevant metabolites in agricultural products based on multifunction dispersive solid-phase extraction and liquid chromatography-mass spectrometry

摘要

A fast and flexible multi-residue procedure for effective extraction of benzimidazole fungicides and the related transformation products in various raw agricultural commodities is developed for direct and simultaneous analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The new sample preparation method, introduced to allow direct extraction of the labile fungicides as the intact forms in complex matrices, is achieved using a conservative homogenizing extraction and multifunction adsorption cleanup (CHEMAC), which basically involves salting-out partitioning/extraction with acetate-buffered acetonitrile at low-temperature and sequential rapid solid-phase dispersive cleanup with a ternary sorbent mixture. The CHEMAC procedure was optimized and further modified by incorporating several pretreatment variables influencing sample stability and process efficiency, such as pH, temperature, salt and sorbent utilized. By using CHEMAC, a noteworthy improvement in extraction recoveries was obtained for the problematic fungicides, while no significant differential matrix effects were detected on the LC-MS/MS analysis in all 9 matrices. The in-source fragmentation of benomyl occurred but caused no cross-talk interference in multi-component analysis. Thus the CHEMAC-based LC-MS/MS strategy can serve as an attractive approach to satisfactory overall process efficiencies (70-92%) with acceptable repeatability (relative standard deviations below 16%) for all the analyte-matrix combinations. Mean accuracies were obtained within the range of 70-110% at fortified levels of 1-500. ng/g, with intra-day and inter-day variations less than 15 and 20%, respectively. The successful practical application of the proposed method to real samples has also been demonstrated.