Analysis of residual oxytetracycline in fresh milk using polymer reversed-phase column

A simple and rapid reversed phase high performance liquid chromatograph (HPLC) method for analysis of oxytetracycline (OTC) was developed and applied in the determination of the antibiotic in fresh milk sample. Isocratic elution was performed with acetic acid:water (pH 4.5):acetonitrile (4:68:28), using a polymer reversed-phase (PLRP) column and UV detection at 354 nm wavelength. The average recoveries of OTC spiked milk at 0.1, 0.2, 0.5 and 100 ng/mL were in excess of 92% with intraday and interday precision between 0.8% and 6.6% respectively. A good linearity was established between the range 100–1000 ng/mL with r2 = 0.9995. The limit of detection and quantitation were 30 and 100 ng/mL respectively. The method demonstrated successful application for analysis of 100 milk samples. Two samples out of 70 from livestock keepers tested OTC positive while none of the 30 samples from milk centers tested positive.