Analytical standard of ASM, (purity 99.5%) was purchased from Wako Pure Chemical Industries Ltd. (Osaka, Japan) and its acidic metabolite benzo[1,2,3]thiadiazole-7-carboxylic acid (CGA 210007), (purity 99.2%) was donated by Syngenta (Basel,Switzerland). Individual stock solutions (1 mg mL−1) of each compound were prepared by dissolving accurately weighed amounts in methanol and stored in darkness at -25◦C. Working standard solutions were prepared by serial dilutions in methanol for the preparation of fortified samples and in mobile phase for the construction of calibration curves. All working standard solutions were stored under refrigerated conditions (4–5◦C).