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...

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