Determination of Oxytetracycline/Oxytetracycline Hydrochloride in Animal Feed, Fish Feed, and Veterinary Medicinal Products by Liquid Chromatography with Fluorescence Detection: Collaborative Study

A method for determining oxytetracycline (OTC) in animal feed, fish feed, and veterinary medicinal products at medicated use and contamination levels was collaboratively studied. The method is applicable to the analysis of animal feeds and mineral premixes containing levels >or=2 mg/kg, and fish feed containing levels >or=10 mg/kg. Oxytetracycline hydrochloride (OTC.HCl) is extracted from ground feed material in acid-methanol solution using mechanical agitation. After centrifugation for 5 min at 1230 x g, an aliquot of the extract is diluted with water and/or acid-methanol so that the concentration of OTC.HCl is approximately the same as that in the working standard, and the solutions contain at least 50% water. Injectable veterinary medicinal materials (also called animal remedy materials) are diluted with water and/or extractant to reach the target concentration. The extracts are filtered and analyzed by reversed-phase liquid chromatography with fluorescence detection with excitation at 390 nm and emission at 512 nm. Twenty-eight test samples of medicated feeds, supplements, and drug premixes, including 4 test samples for trace-level analysis, were sent to 17 collaborators in Canada, The Netherlands, and the United States. Results were received from 11 laboratories. The RSD(r) values (within-laboratory repeatability) ranged from 1.26 to 9.21%; RSD(R) values (among-laboratory reproducibility) ranged from 2.14 to 12.9%, and HorRat values ranged from 0.54 to 3.02. It is recommended that this method be adopted AOAC Official First Action.