Instrumentation for Multi-Electrode Voltammetry

When metal pollutants exist in natural water, their toxicity is dramatically dependent on the chemical species. Numerous sophisticated techniques and instruments have been developed to detect metal pollutants at very low concentration levels. However, one important factor is often ignored, i.e., rarely is species determination required. Electrochemical (EC) methods have the particular advantage of being, in principle, a species-sensitive method rather than an element-sensitive method for the study of metal speciation in natural waters. The goal of this research was to develop an instrument using the EC technique for speciation and general voltammetric studies. It was accomplished by designing a flow-through EC cell containing multi-electrodes to which various fixed potentials over a selected range were applied. A special potentiostat was designed to supply a selected potential to each electrode in the cell. Potential control was provided by placing a combined counter-reference electrode at circuit ground and connecting each working electrode to the inverting input of a current follower which had a potential applied to its non-inverting input from two digital-to-analog converters and a resistor network. Integrating current followers were used for measuring signal currents generated by the electrolytes samples on each electrode. A multiplexing circuit, including an analog-to-digital converter, was used to fulfill data acquisition. These circuits were interfaced to a computer and the readout was a pseudo-voltammogram which is a plot of amperometric currents versus various applied fixed potentials on each electrode. Details of the instrumentation, software, and some initial results are described.