Voltametric and flow injection determination of oxytetracycline residues in food samples using carbon fiber microelectrodes

A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square-wave conditions, a linear calibration plot for OTC was obtained in the 1.0 x 10(-6)-1.0 x 10(-4) mol L-1 range, with a detection limit of 2.9 x 10(-7) mol L-1 (150 ng mL(-1)) OTC. The determination of OTC by a flow-injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL(-1) and 200 ng g(-1) levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile -5.0 x 10(-4) mol L-1 tetrabutylammonium perchlorate medium. Recoveries of 96+/-8 and 91+/-8% were obtained for milk and eggs, respectively, by applying the standard additions method.