VOLTAMMETRIC AND AMPEROMETRIC STUDIES OF THIOCHOLINE AT A SCREEN-PRINTED CARBON ELECTRODE CHEMICALLY-MODIFIED WITH COBALT PHTHALOCYANINE - STUDIES TOWARDS A PESTICIDE SENSOR

Cyclic voltammetry was used to investigate the electrochemical behaviour of thiocholine at screen-printed carbon electrodes chemically modified with cobalt phthalocyanine. Cyclic voltammograms exhibited one anodic peak (Ia) and two cathodic peaks (Ic and IIc) in the potential range -0.8-+0.3 V between pH 5.0 and 12.0. Peak Ia is considered to result from the electrocatalytic oxidation of the thiol moiety to produce the corresponding disulfide; peak Ic is likely to be the electrocatalytic reduction of the disulfide back to the original thiol species. Peak IIc is probably due to a reduction process occurring in the macrocyclic phthalocyanine molecule. Hydrodynamic voltammetry was performed in 0.05 mol dm(-3) phosphate buffer (pH 8.0) containing thiocholine; one well-defined anodic wave was obtained. From this, the optimum potential for amperometric studies was found to be +0.1 V. Calibration studies were performed using amperometry in stirred solution; a linear response was obtained over the range 5.0 X 10(-7)-4.8 X 10(-5) mol dm(-3). It should be possible to use these screen-printed electrodes as the basis of a pesticide sensor.