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 humanand veterinary medicine due to their broad-spectrum activity against most Gram-positive andGram-negative bacteria (1). When tetracycline drugs are administered by laymen, as in mostcases, correct dosages and withdrawal periods are unlikely to be observed. This raises concernsthat 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 thedetermination of trace amounts of tetracycline based on a poly (thionine) film which iseffectively shuttle electrons between the analyte and the base electrode. Generally, thepreparation of conducting films by electropolymerization of a monomer which itself was a redoxmediator has been demonstrated to enhance the sensivity of the electrochemical sensor (3). In thepresent work, electropolymerization of thionine on the surface of a carbon nanotube pasteelectrode provided a chemically modified electrode which responded linearly to the concentrationof tetracycline, shifted the peak potential of tetracycline negatively and increased the peakcurrent. Electrochemical behavior of tetracycline at the surface of poly(thionine)-modified carbonnanotube paste electrode was fully characterized using cyclic voltammetry andchronoamperommetry. Moreover, the effect of different experimental parameters including pH,on the electrochemical current of tetracycline was evaluated. Under the optimized conditions, theproposed electrode showed linear dependence of peak current with the concentration of tetracycline within the range of 0.50-20.0 mM with the detection limit of 0.46 mM. Finally,tetracycline tablet and urine samples were analyzed for tetracycline with the presented methodusing standard addition. The obtained recoveries indicated the accuracy and applicability of themethod.