CONVECTION DIFFUSION-CONTROLLED AND DIFFUSION-CONTROLLED RAPID-SCAN VOLTAMMETRY IN LIQUID-CHROMATOGRAPHIC SYSTEMS WITH A LARGE-VOLUME WALL-JET DETECTOR

On-line voltammetric measurements under liquid chromatographic (LC) conditions yield voltammograms which are either purely diffusion- or purely convection/diffusion-controlled, or a combination of both. The dependence of this behaviour on flow-rate, scan-rate and electrode diameter is investigated for a large-volume wall-jet detector. It is shown that for 4 V s-1 scan-rates at 1 ml min-1 flow-rates (conventional LC conditions), S-shaped (convection/diffusion-controlled) voltammograms can be obtained with macro-electrodes (≥ 1 mm diameter). Distortion of voltammogram shape by the cell time constant is discussed for macro-electrodes. The behaviour of the cell in microbore and micro-LC applications is demonstrated. The advantage of being able to change from convection/diffusion-controlled to diffusion-controlled behaviour is discussed. © 1990.