DEVELOPMENT OF GRAPHITE-POLY(TETRAFLUOROETHYLENE) COMPOSITE ELECTRODES - VOLTAMMETRIC DETERMINATION OF THE HERBICIDES THIRAM AND DISULFIRAM

The oxidative voltammetric behaviour of the herbicides thiram and disulfiram at graphite-poly(tetrafluoroethylene) (PTFE) composite electrodes has been studied. Graphite-PTFE pellets were prepared by mixing graphite with powdered PTFE and compression molding the mixture. Based on the signal-to-noise characteristics and on the mechanical strength of the resulting pellet, a mixture containing 40% PTFE was selected. Both thiram and disulfiram are adsorbed onto the composite electrode, this process being used as a preconcentration step. The accumulation potential and accumulation time chosen were 0.0 V and 300 s, respectively. The characteristics of the electrode processes were established. Linear calibration graphs were obtained within the ranges 2.0 x 10(-7)-1.0 x 10(-5) and 2.0 x 10(-7)-8.0 x 10(-6) mol l(-1) for thiram and disulfiram, respectively. The effect of the presence of ziram, phenol and Zn(II) on the oxidation signals for thiram and disulfiram was evaluated. As an application, the determination of thiram in spiked strawberries was carried out with good results.