Alkaline hydrolysis assisted UHPLC-MS/MS for simultaneous determination of MCPA and fluroxypyr residues in rice fields and its validation

The extensive use of 2-methyl-4-chlorophenoxyacetic acid (MCPA) and fluroxypyr herbicides in rice cultivation necessitates monitoring to ensure food safety. However, the simultaneous determination of these compounds is challenging due to complex residue definitions, which encompass acids, conjugates, and salts. To address this problem, we developed a robust alkaline hydrolysis-assisted UHPLC-MS/MS method for the simultaneous quantification of MCPA, fluroxypyr, and their ester/salt conjugates in rice matrices (brown rice, husk and straw). Validation demonstrated satisfactory performance: accuracy (recoveries of 77.8–105%), precision (RSDs 0.5–10.6%), linearity (R 2 ≥ 0.999), and sensitivity (LOD 0.008–1 μg/kg, LOQ 0.24–3 μg/kg and mLOQ 10 μg/kg). Analysis of 24 rice samples from 12 provinces revealed all target residues in brown rice and straw were below mLOQs, while trace levels (1.59–3.42 μg/kg) in rice husk remained far below Chinese maximum residue limits (MRLs) in brown rice, indicating negligible consumer risk. This effective and sensitive approach supports food safety monitoring and risk assessment. • A novel alkaline hydrolysis-based method for MCPA and fluroxypyr residues in rice matrices. • An efficient extraction and cleanup procedure was established using salting-out and MAX-SPE. • It complies with JMPR, EFSA, and EPA residue definitions for dietary risk assessment. • The method is accurate, precise, and fully meets validation criteria of both Chinese and EU guidelines. • This method was successfully applied to 24 field samples confirmed its practical reliability.