Abstract
As set in the maximum residue limit regulations of the European Commission, this study aimed to obtain the residual parameters in milk with optimized UPLC-MS/MS conditions and to determine the conclusive drug withdrawal period to ensure food safety. In this research, an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to study cefquinome sulfate's residue elimination in milk and to calculate cefquinome's withdrawal period. Twelve healthy cows free of endometritis were selected for the experiment. Before using the drug, the vaginal orifice and perineum of each cow was disinfected. One dose of intrauterine perfusion was used for each cow, followed by an additional dose after 72 h. Before administration and 12 h, 18 h, 24 h, 36 h, 42 h, 48 h, 60 h, 66 h, 72 h, 84 h, 90 h, and 96 h after the last dose, milk (10 mL) was gathered from each cow's teat and pooled. For the measurement of cefquinome concentrations in milk, UPLC-MS/MS was performed. A calibration curve was generated using linear regression as follows: Y = 250.86X - 102.29, with a correlation coefficient of 0.9996; the limits of detection and the limits of quantitation were 0.1 μg·kg(-1) and 0.2 μg·kg(-1), respectively. The average recovery of cefquinome was 88.60 ± 16.33% at 0.2 μg·kg(-1), 100.95 ± 2.54% at 10 μg·kg(-1), and 97.29 ± 1.77% at 50 μg·kg(-1). For 5 consecutive days at the three spiking levels, the intra and inter-day relative standard deviations (RSD) were 1.28%-13.73% and 1.81%-18.44%, respectively; the residual amount of cefquinome was less than the maximum residue limit of 20 μg·kg(-1), 36 h after administration; and the residual amount was less than the limit of detection (0.1 μg·kg(-1)) 48 h after administration. The withdrawal time of cefquinome in cow's milk was 39.8 h, as calculated using WTM1.4 software. In terms of clinical practical use, the withdrawal period of milk was temporarily set at 48 h after the administration of the cefquinome sulfate uterus injection to cows, in accordance with the recommended dose and course.