Fundamental investigations and applications of microelectrode based detections in flowing solutions

Abstract: The influence of diffusional, migrational and convective mass transport at microelectrodes employed for voltammetric and amperometric detection in flowing solutions has been investigated. Special attention was paid to the influence of convection on the IR drop in organic solvents and on the transport of reaction products between individual electrode bands of microarray electrodes. A flow injection system was also designed to study the stability of mercury films coated on microelectrodes for the purpose of stripping analysis.Increased influence of convection, obtained by altering the flow rate or by changing the position of the microelectrode in a wall-tube flow cell, at low support ratios in organic solvents was found to result in decreased currents as a consequence of the inability to maintain a sufficient amount of ions at the vicinity of the microelectrode surface. Successful determinations of the water content in butter and margarine could be performed in an acetone based flow injection system, provided that the detection potential was chosen to accommodate the different support ratios in the injected solutions.The degree of redox cycling at interdigitated microarray electrodes was found to increase if the flow rate was reduced from 20 to 2 µl/min. Even at these low flow rates, the degree of redox cycling in stationary solutions was, however, always larger compared to the values obtained under the influence of convection. A microarray electrode was also employed to improve the selectivity in the detection of poorly separated species in capillary electrophoresis.By employing a flow injection system, it was found that the stability of mercury films plated on platinum and carbon fibre microelectrodes could be improved as potential control could be maintained during solution exchange and between individual experiments. Stripping voltammetric determinations of nickel at nM concentrations and of copper in a low ionic strength solution was demonstrated in the flow injection system.