Verification of Official LC-MS/MS Methods and Nationwide Monitoring of Five Prohibited Veterinary Drugs and a Major Metabolite in Livestock Muscle in Korea

This study evaluated the fitness for purpose of official Korean Food Code LC-MS/MS methods for five prohibited veterinary drugs and one major metabolite—pyrimethamine, dapsone, monoacetyldapsone, roxarsone, chloramphenicol, and vancomycin—in bovine, porcine, and chicken muscle and applied the evaluated methods to nationwide monitoring of production-stage samples. In 2024, dapsone, monoacetyldapsone, pyrimethamine, and roxarsone were analyzed in 202 muscle samples, whereas in 2025, chloramphenicol and vancomycin were analyzed in 300 muscle samples (total n = 502). Analytical performance was assessed for selectivity, linearity, limits of detection (LOD) and quantification (LOQ), recovery, repeatability, inter-day precision, and between-analyst performance; all analyte–matrix combinations met the predefined acceptance criteria. For chloramphenicol, an LOQ of 0.15 μg/kg was achieved in all three matrices, equal to the European Union reference point for action. An external proficiency test for chloramphenicol in bovine muscle yielded a satisfactory z-score of −0.30. No sample met the regulatory reporting criterion for any target analyte included in the respective annual survey. These findings support the fitness for purpose of the evaluated official methods and provide baseline analytical and occurrence data for surveillance of selected prohibited substances in production-stage meat in Korea.