GC–MS/MS method for determining quizalofop ethyl, quizalofop tefuryl, and their metabolites in foods

A gas chromatography–tandem mass spectrometry (GC–MS/MS) method was developed for the quantitative analyses of quizalofop ethyl and quizalofop tefuryl herbicides as well as their metabolites (i.e., quizalofop and its conjugates). This method fulfills the residue definition established by Japan. Following sample reflux in a methanolic potassium hydroxide solution, the residues were converted to 6-chloro-2-methoxyquinoxaline (CMQ) and extracted with hexane. Cleanup was carried out using primary secondary amine and silica gel cartridges prior to GC–MS/MS analysis. The developed method was validated for quizalofop ethyl, quizalofop tefuryl, and quizalofop in six foods at 0.01 mg/kg and at their maximum residue limits set by Japan. A satisfactory analytical performance was achieved (trueness = 80–93%, relative standard deviation = 1–7%, limit of detection = 0.00025 mg/kg for all analytes), and no significant matrix effects were observed for the examined matrices. There were no interfering peaks near the retention time of CMQ, indicating the high selectivity of this method. A satisfactory recovery was also achieved for propaquizafop in soybeans, indicating that the proposed method also complies with the residue definition established by the European Union. This method is suitable for the regulatory analysis of quizalofop ethyl and quizalofop tefuryl residues.