Development of an LC–MS/MS-based method for determination of acetochlor and its metabolites in crops

[Display omitted] •LC–MS/MS-based method for acetochlor residue quantification was developed.•Acetochlor and its metabolites were hydrolyzed to EMA and HEMA.•The method complies with the residue definition recommended by the JMPR.•Hydrolysis was performed in a vial instead of a hydrolysis-distillation apparatus.•The method showed satisfactory analytical performance for soybeans and sweet corn. A reliable quantitative method was developed to determine acetochlor residues in soybeans and sweet corn by using liquid chromatography-tandem mass spectrometry (LC–MS/MS). Acetochlor and its metabolites were analyzed as the sum of compounds converted to 2-ethyl-6-methylaniline (EMA) and 2-(1-hydroxyethyl)-6-methylaniline (HEMA) during hydrolysis, expressed as acetochlor equivalent, according to the residual definition used by the United States and Japan. The method involved sample homogenization in methanol, heating at 120 °C under strongly basic conditions (methanol/50 % (w/w) sodium hydroxide solution (1:1, v/v)) in a glass vial to convert acetochlor and its metabolites to EMA or HEMA, cleanup using a strong anion-exchange polymer-based cartridge, and subsequent analysis using LC–MS/MS. The developed method was validated for acetochlor as an EMA-producing compound and 2-[(ethoxymethyl){2-(1-hydroxyethyl)-6-methylphenyl}amino]-2-oxoacetic acid (EHO) as a HEMA-producing compound in soybeans and sweet corn. Excellent analytical performances were observed for acetochlor and EHO, with the average recoveries of 82 %–92 % and relative standard deviations of 1%–3%. No interference was observed near the retention times of EMA and HEMA, which indicated high selectivity. Overall, the developed method is viable for regulatory analysis of acetochlor residues.