Voltammetric determination of tetracycline at the surface of poly (thionine)- modified carbon nanotube paste electrode

Tetracylines (TCs) produced by Streptomyces spp. are a large family of antibiotics used in human and veterinary medicine due to their broad-spectrum activity against most Gram-positive and Gram-negative bacteria (1). When tetracycline drugs are administered by laymen, as in most cases, correct dosages and withdrawal periods are unlikely to be observed. This raises concerns that animal tissue intended for human consumption might be contaminated with residues of TCs (2). Herein, a simple, rapid, accurate and sensitive electrochemical sensor is described for the determination of trace amounts of tetracycline based on a poly (thionine) film which is effectively shuttle electrons between the analyte and the base electrode. Generally, the preparation of conducting films by electropolymerization of a monomer which itself was a redox mediator has been demonstrated to enhance the sensivity of the electrochemical sensor (3). In the present work, electropolymerization of thionine on the surface of a carbon nanotube paste electrode provided a chemically modified electrode which responded linearly to the concentration of tetracycline, shifted the peak potential of tetracycline negatively and increased the peak current. Electrochemical behavior of tetracycline at the surface of poly(thionine)-modified carbon nanotube paste electrode was fully characterized using cyclic voltammetry and chronoamperommetry. Moreover, the effect of different experimental parameters including pH, on the electrochemical current of tetracycline was evaluated. Under the optimized conditions, the proposed electrode showed linear dependence of peak current with the concentration of 332 tetracycline within the range of 0.50-20.0 μM with the detection limit of 0.46 μM. Finally, tetracycline tablet and urine samples were analyzed for tetracycline with the presented method using standard addition. The obtained recoveries indicated the accuracy and applicability of the method.