Determination of carbendazim, thiophanate, thiophanate-methyl and benomyl residues in agricultural products by liquid chromatography-tandem mass spectrometry

A simple and reliable liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed for carbendazim (MBC), thiophanate (TE), thiophanate-methyl (TM) and benomyl (BM) in agricultural products. These compounds were extracted from agricultural products with methanol after addition of sodium L-ascorbate. BM was hydrolyzed to MBC during the extraction with methanol. TE and TM were cyclized to ethyl 2-benzimidazole carbamate (EBC) and MBC by refluxing at 120 °C for 30 min with copper acetate in 50% acetic acid. MBC and EBC were cleaned up by an n-hexane wash and extraction with ethyl acetate and determined by LC-MS/MS. The mean recoveries from 10 agricultural products were in the range of 75.8-100.0%, and the relative standard deviations of 5 experiments were in the range of 1.5-9.2% at concentrations equal to the maximum residue limits (MRLs). The calibration curves were made by using commercial MBC and EBC as reference analytical standards without refluxing. The quantification limits were 0.01 mg/kg (as MBC), which is the uniform limit in the positive list system for agricultural chemical residues in foods in Japan.