Abstract: Objective: To establish a SPE-HPLC method for the simultaneous determination of multi-tetracyclines(TCs) residues in milk. Method: The TCs in 5g milk sample was extracted with 20ml EDTA-Mcllvain buffer, then after centrifugation, the 5ml supernatant liquid was loaded on an preconditioned SPE Sep-Pak? C18 cartridge. The TCs was eluted with 3ml 10mmol/L oxalic acid methanol following the rinse clean-up. Then eluant was evaporated with N2 to dryness at 40℃, and the residues was redissolved with 0.5ml HPLC flow phase and detected with HPLC method. Results: The calibration curve was linear in the range 0.05-1.0mg/ L and r>0.99. The limit of quantification (LOQ) was 0.025, 0.025, 0.05 and 0.05mg/L respectively for oxytetracyline, tetracycline, chlortetracycline and doxytetracyline residues in milk, and at the corresponding spike level 0.1, 0.1, 0.2 and 0.2mg/L respectively. The recovery rates were 84%￣110% and RSD<10%. Conclusion:The method was applicable for the detection of TCs residues in milk. The clean-up effect, sensitivity, accuracy and prevision have all met the analysis requirement.

Key words: milk, multi-tetracyclines residues, SPE, HPLC