An optimized LC-MS/MS workflow for evaluating storage stability of fluroxypyr and halosulfuron-methyl in maize...

Pesticide registration ensures the safety of agricultural products; however, the backlog of field samples often requires lengthy storage periods. Thus, the stability of pesticide residues in stored samples is required information for pesticide registration. We monitored the degradation rates of fluroxypyr and halosulfuron-methyl in maize straw, mature maize grain, and fresh corn matrices to evaluate their storage stability. Analytes were extracted and cleaned up with a modified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method and then detected with liquid chromatography tandem-mass spectrometry. We optimized the workflow by testing different clean-up sorbents, LC columns, and chromatographic methods. The linearity correlation coefficients of fluroxypyr and halosulfuron-methyl in the three matrices were ≥0.994. At three fortification levels, the mean recoveries of fluroxypyr and halosulfuron-methyl were 84.2-114.8% and 83.8-105.5% with relative standard deviations of 2.4-9.4% and 2.7-10.2%, respectively. Degradation of the two herbicides in the three matrices was less than 30% over the 70-day storage period, indicating fluroxypyr and halosulfuron-methyl are stable in the tested maize matrices when stored at -20 °C for at least 70 days. This study provides a reference method for pesticide residue analysis and can be used as a guide to develop accurate and reasonable pesticide registration procedures.