HPLC-ELECTROCHEMICAL DETECTION WITH GRAPHITE-POLY(TETRAFLUOROETHYLENE) ELECTRODE - DETERMINATION OF THE FUNGICIDES THIRAM AND DISULFIRAM

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflo n) electrodes as amperometric indicator electrodes in HPLC detection i s demonstrated. The determination of the fungicides thiram and disulfi ram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the org anic solvent used in the mobile phase as well as its percentage, the p otential applied to the composite electrode, and the time elapsed betw een mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonit rile percentage used in the mobile phase on the retention of thiram, d isulfiram, ziram and phenol was evaluated. Resolution up to the baseli ne can be achieved with 45% acetonitrile. The sensitivity of the deter mination of thiram and disulfiram in the presence of a constant concen tration of ziram is slightly better when using a wall-jet cell; howeve r, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before th e injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow ce ll configuration. As an application, the determination of thiram in sp iked apple samples, at a level of 0.5 mg thiram kg(-1) apple, has been carried out with a mean recovery of 97 +/- 3% for a significance leve l of 0.05.