Electrochemical sensor for heparin based on a poly(thionine) modified glassy carbon electrode

A poly(thionine) thin film modified electrode was successfully assembled on the surface of the glassy carbon electrode by means of electrochemical polymerization, which was carried out with cyclic voltammetric sweeping in the potential range 0 to +1.4 V (vs. Ag/AgCl) in perchloric acid solution containing 0.1 mmol L^?1 thionine. The film modified electrode exhibited a couple of well-defined redox peaks, and the redox peaks decreased correspondingly without a shift of the peak potential after the addition of heparin. The conditions of the binding reaction and the electrochemical detection were optimized. Under the optimum conditions the decrease of the peak current was proportional to the concentration of heparin in the range 4.0 to 22.0 μg mL^?1 and the detection limit was 0.28 μg mL^?1. The relative standard deviation (RSD) for five parallel determinations of 10.0 μg mL^?1 heparin was 0.93%. The effects of potentially interfering species were investigated and the method was successfully applied to the determination of heparin in a pharmaceutical formulation.