Determination of oxytetracycline and its degradation products by high-performance liquid chromatography–tandem mass spectrometry in manure-containing anaerobic test systems

This paper describes the development of a HPLC–MS–MS (ESI) method with baseline separation of oxytetracycline, 4-epi-oxytetracycline, α-apo-oxytetracycline and β-apo-oxytetracycline using an XTerra column and an MeOH–MilliQ-water (containing 8 mM formic acid) mobile phase. Limits of quantification for aqueous standards were in the range of 0.004 to 0.008 μM. The linear range tested was 0.003 to 0.5 μM and in one case up to 17 μM. An experiment simulating the degradation of oxytetracycline in manure was set up and free concentrations of the four antibiotics were determined during 6 months. Oxytetracycline (>0.02 μM) was observed up till 6 months after spiking. No important increase in free concentrations of the degradation products was observed.