RP-HPLC determination of tetracycline and oxytetracycline residues in milk

Objective:To establish an HPLC method for the determination of tetracycline and oxytetracycline residues in fresh milk and initial assess the milk quality of some brands in Tianjin market.Methods:Matrix solid phase dis- persion(MSPD)and Solid phase extraction(SPE)were used in samples'pretreatment.On prepared C_(18)column,u- sing methanol-acetonitrile-0.01 mol·L~(-1)oxalic acid solution(pH 2.0)(11:22:67)as mobile phase.The flow rate was 1.0 mL·min~(-1)and the UV detector wavelength was 255nm.Result:The mixture including standard anti- biotics samples were detected and tetracycline and oxytetracycline were successfully separated on baseline within 5 min.The linear ranges of tetracycline and oxytetracycline were from 0.01 to 0.05μg·mL~(-1),the average recovery was 93.9% and 89.6% respectively.The RSD ranged from 1.02% to 6.81%.6 brands of fresh milk on sell and 2 kinds of fresh milk on farm were determined using this method,but no tetracycline and oxytetracycline residues were detected.It show that the milk products in Tianjin area are safety by and large.Conclusion:The MSPD- HPLC-UV method is accurate and reliable,suitable for the determination of tetracycline and oxytetracycline resi- dues in fresh milk.