Simultaneous determination of roxithromycin and three tetracyclines in manure by high-performance liquid chromatography with a diode-array detector

An analytical method for the simultaneous determination of roxithromycin,oxytetracycline,tetracycline and chlortetracycline in manure was developed by solid phase extraction and high-performance liquid chromatography with a diode-array detector.A centrifuged sample(2 g) was ultrasonically extracted with 15 mL of a mixture of EDTA and McIlvaine buffer(citric acid and sodium orthophosphate) for 15 min.Then the extract was evaporated and cleaned up on a HLB cartridge.The final eluate(methanol) was concentrated before injection.Using acetonitrile and 0.03 mol /L ammonium dihydrogen phosphate(pH 2.0) as the mobile phase,roxithromycin was obtained good linear calibrations in the range of 1.5 ~ 600 mg /L,oxytetracycline,tetracycline and chlortetracycline were obtained good linear calibrations in the range of 0.25 ~ 100 mg /L.And the correlation coefficients were 0.9995 ~ 0.9999,respectively.The limits of detection(LOD) and the limits of quantification(LOQ) were 0.06 ~0.38 mg/kg(S/N =3) and 0.2 ~1.2 mg/kg(S/N =10) in manure,respectively.The average recoveries were in the range of 52.2% ~ 64.7% when the spiked concentrations were 15 mg /kg roxithromycin,2.5 mg /kg oxytetracycline,tetracycline and chlortetracycline.The RSD ranged from 7.3% to 8.4%.This method is accurate,rapid and sensitive during the inspection of antibiotics in real samples.