Quantitative analysis for oxytetracycline in medicated premixes and feeds by second-derivative synchronous spectrofluorimetry Original Research Article

A spectrofluorimetric method for the determination of oxytetracycline (OTC) in medicated feeds and premixes is described. OTC is used alone without combination with other tetracyclines. The method involves sample dissolution in methanol:water (50:50) in the case of medicated premixes, and triple extraction with 1% (w/v) Na2·EDTA methanol:water (50:50) in the case of medicated feeds. Determination of OTC in the diluted extract is based on the reaction of the drug with divalent metal ions (Ca2+) at pH=6–10 to form a yellow complex that can be analyzed by synchronous spectrofluorimetry (Δλ=115 nm). The applicability of the validated method was tested by analyzing commercial medicated premixes and feeds without any interference from the matrix. OTC determination in feeds was also not affected by the presence of other common drugs such as sulfamethazine and colistin sulfate that are not fluorescent.