The Animal and Plant Quarantine Agency conducts a targeted sampling plan and analysis for veterinary drugs within the country every year. Target compounds included tetrachlorvinphos as an organophosphate, diminazene as an anti-infective medication, ketoprofen as a nonsteroidal anti-inflammatory drug, triclabendazole and clorsulon as flukicides in 2022. These compounds were not included in National Residues Program (NRP), despite their high sales ranking. A total of 94 bovine muscle samples and 20 equine muscle samples were collected from various locations across the country. The analysis of target compounds in muscle was performed using LC-MS/MS coupled with Food code 8.3.1 revised in 2022. A 2 g sample of muscle tissue was extracted using a water: acetonitrile (1:4, v/v) solution, then cleaned up with C18 and hexane saturated with acetonitrile. Compounds were separated with C18 column and mobile phases consisted of 0.1% formic acid in water (A) and 0.1% formic acid in acetonitrile (B). All analytes exhibited good linearity with correlation coefficients (R2) higher than 0.992. The limit of quantification (LOQ) of these compounds ranged from 0.21 to 2.79 μg/kg except for diminazene (3.85~6.86 μg/kg). The average recoveries of these analytes were 89.45~129.13% in muscle at spiked level of 10 or 20 μg/kg. Relative standard deviations (%) (intra-day and inter-day) were lower than 20% for all target compounds, except for diminazene and triclabendazole, whose intra-day RSD % was slightly higher than 20% in equine muscle. Testing confirmed that all 94 bovine and 20 equine muscle samples from 9 provinces were free from residues of veterinary drugs. Monitoring of compounds not included in the NRP should continue to ensure consumer health and food safety.

This study aims to establish a modified analytical method with sensitivity and reliability for streptomycin (STP) and dihydrostreptomycin (DHS) of residues level in pig tissues, plasma and urine by LC-MS/MS on the basis of previous studies. The mass parameters of quantitative and qualitative ions for STP and DHS were optimized using multiple reaction monitoring in positive mode. The separation of compounds was conducted using BEH Amide column according to material’s characteristics. The analytes in plasma were extracted with only organic solvents. In muscle and kidney, KH2PO4 buffer solution containing 2% CCl3COOH and EDTA-Na was used as extraction solvent. The WCX cartridege was selected as SPE cartridge in considering high recoveries for STP and DHS. The analytes in urine were extracted by organic solvents with acid and addition of EDTA. The limits of detection (LODs) in STP and DHS ranged 0.45~3.66 μg/kg and 0.22~0.78 μg/kg, respectively. The limits of quantification (LOQs) were 1.35~11.10 μg/kg in STP and 0.66~2.36 μg/kg in DHS. The recoveries (%) were 94.29~104.5% in STP and 92.32~108.45% in DHS except for plasma with lower values (61.45/68.5%, respectively). In the precision evaluation, the coefficient of variation (CV, %) of STP showed <10.50% on intra-day and <18.04% on inter-day. The CV (%) of DHS showed <8.42% on intra-day, whereas <17.98% on inter-day. The modified method is reliable for continuous residual monitoring in pig to ensure food safety for consumer’s health. In addition, this method could be used in study relation to residue depletion and pharmacokinetics of veterinary drug.