Simultaneous quantification of oxyclozanide and levamisole in milk via ultra-high-performance liquid chromatography tandem mass spectrometry: A validated high-sensitivity approach for veterinary residue surveillance

This study developed a novel analytical method integrating liquid-liquid extraction with solid-phase extraction for simultaneous detection of oxyclozanide (OXY) and levamisole hydrochloride (LMS) residues in milk using ultra-high-performance liquid chromatography tandem MS (UPLC-MS/MS). Method validation demonstrated exceptional sensitivity with detection limits of 1.00 ng/mL and quantitation limits of 3.00 ng/mL for both analytes. Low matrix effects (CV <8.00%) and satisfactory recoveries (OXY: 84.00%-108.77%, relative SD [RSD]: 2.20%-8.00%; LMS: 89.50%-119.60%, RSD: 2.10%-8.36%) were achieved across multiple validation parameters, while sample stability remained consistent under varied processing conditions (CV <10.00%). Analysis of 120 commercial milk samples revealed no detectable residues, confirming both the reliability of this monitoring framework and the compliance of Chinese dairy products with international safety standards. As the first reported method enabling concurrent detection of this antiparasitic drug combination, the established protocol provides crucial technical support for veterinary drug residue surveillance, ensuring safer application of compound oxyclozanide suspension in livestock husbandry.