Study On The Residues Determination Method Of Some Veterinary Drugs And Its Detection In Milk

High performance liquid chromatography-tandem mass spectrometry(HPLCMS/MS) is the mainstream technique to detect veterinary drug residues. The analytical method was established for simultaneously detecting residues of four parasiticides(praziquantel, ivermectin, avermectin and doramectin) in milk with the ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). Meanwhile, the residue of dexamethasone in milk was detected by enzyme-linked immunosorbent assay.1. A new multi-residue analytical method was developed for the simultaneous determination on the residues of 4 parasiticides, praziquantel, ivermectin, abamectin and doramectin, in milk with ultra-high performance liquid chromatography tandem mass spectrometry(UPLC-MS-MS). The samples were extracted with acetonitrile and then cleaned up with alkaline alumina column. The target compounds were separated with UPLC ACQUITY BEH C18 column. The mobile phase A(acetonitrile plus 0.1% formic acid) and the mobile phase B(0.1% formic acid plus 5 mmol/L ammonium acetate) were used in a gradient elution program. Several UPLC-MS/MS conditions which included the mobile phase, monitor ions and extractant were optimized. The target drugs were detected by electrospray ionization mass spectrometry in positive ion mode with multiple reaction monitoring. The results showed that there was a good linear relationship in the range of 5.0~100.0 ng/mL and the correlation coefficients of determination methods for four drugs were all above 0.996. Precision and accuracy of the method was investigated at three spiked levels(5.0, 10.0 and 20 μg/kg). The average recoveries of determination methods for four drugs were in the range of 76.4% to 113.3%(n=6), and its relative standard deviations(RSDs) were in the range of 2.4% to 10.6%(n=6). The limits of detection(LODs) for praziquantel, ivermectin, abamectin and doramectin were 1.0, 2.5, 2.5 and 2.5 μg/kg, and the limits of quantitation(LOQs) were 2.0, 5.0, 5.0 and 5.0 μg/kg, respectively. The limits of detection(LODs) of ivermectin in milk were lower than the maximum residue limit(MRL)(10 μg/kg) established by the Chinese legislation. The method was simple, rapid, and accurate to measure the residues of the four parasiticides.2. Fresh milk samples were collected from Guiyang city and other regions in Guizhou province. Praziquantel, ivermectin, abamectin and doramectin in milk were detected by UPLC-MS/MS which were developed by us. The results indicated that the sample numbers found out praziquantel, ivermectin, abamectin and doramectin were 11, 1, 5 and 16, and their detection rate of the parasiticides were 5.41%、0.49%、2.46% and 7.88%, respectively.3. 84 milk samples were collected from different sites of containers in six dairy farms of Guiyang, in which 22 samples were identified dexamethasone residues by enzyme-linked immunosorbent assay and the detection rate was 26.2%. One of the 22 samples’ residual content exceeded the national standard and the excessive rate was 7.1%. The highest detection rate of dexamethasone was 71.4%, in the samples milk collected from the front-end of milk containers, which was much higher than the back-end. The results suggested that the dexamethasone can be gradually degraded in containers.