Comparison of direct current, derivative direct current, pulse and square wave voltammetry at single disc, assembly and composite carbon electrodes: stripping voltammetry at thin film mercury microelectrodes with field-based instrumentation

Abstract

A comparative investigation of normal and stripping forms of voltammetry was undertaken at single and random array microdisc, macrodisc and composite carbon electrodes using dc, derivative dc, square-wave and differential-pulse waveforms. Studies on the reduction of [Fe(CN)6]3– in 0.05 M KNO3 revealed that the dc waveform with derivative readout is superior to the use of square-wave or differential-pulse waveforms at both single disc and random array carbon fibre electrodes. Analytical superiority to that obtained at a conventional glassy carbon macrodisc electrode was also observed. The detection limit for the determination of [Fe(CN)6]3– was 4 × 10–6 M at the carbon fibre random array microdisc electrode and 6 × 10–6 M when using a single disc microelectrode (scan rate = 200 mV s–1). For the determination of Pb and Cd in 0.1 M HCl by stripping voltammetry, the ideal combination of high sensitivity (1 ppb detection limit), avoidance of the need to remove oxygen or utilise solution stirring or electrode rotation could be achieved at mercury-plated thin film single disc or random array microelectrodes or composite electrodes. Furthermore, under these thin film conditions, the analytical performance of each of these three electrode types improved with respect to signal-to-background current ratio as the scan rate increased. Consequently, short potential scanning times as well as optimum sensitivity are achieved with scan rates in the 1–50 V s–1 range. All of the results obtained demonstrate that highly sensitive field-based voltammetric analysis may be accomplished using the combination of an inherently simple two-electrode battery operated instrument, the dc waveform and random array or single carbon fibre microdisc working electrodes. An interface which enables voltammetric studies to be undertaken with a battery operated personal computer is described for this purpose.