Column and Mobile Phase Optimization of UPLC-MS/MS for Stable Determination of Acidic Water-Soluble Moroxydine Hydrochloride in Complex Food Samples

Moroxydine hydrochloride (MH) is an acidic and water-soluble pesticide. Our previous study selected trifluoroacetic acid and formic acid for the extraction of MH from food samples with different water contents. Nevertheless, variations in the pH of extracts derived from different food matrices led to the retention time drift of MH, thereby compromising detection stability. This work systematically optimizes the chromatographic conditions, including the chromatographic column and mobile phase for the UPLC-MS/MS method, to achieve the stable quantification of MH. The influence of extraction solution pH on the retention time of MH was investigated across high-water, low-water, and high-oil content plant samples. A 100 mm C18 column was selected for separation. The aqueous mobile phase contained 0.05% trifluoroacetic acid. The initial volume ratio of the aqueous phase to acetonitrile was set at 85:15. Under these conditions, the retention time of MH remained stable at 1.10 min in all food matrices. This study established a stable and sensitive analytical method for quantifying MH residues in agricultural products, in which a matrix-matched calibration is required to compensate for matrix-dependent ionization responses.