Alfonso Berduque

Voltammetric characterisation of silicon-based microelectrode arrays and their application to mercury-free stripping voltammetry of copper ions.

This paper describes the electrochemical characterisation of a range of gold and platinum microelectrode arrays (MEAs) fabricated by standard photolithographic methods. The inter-electrode spacing, geometry, numbers and dimensions of the electrodes in the arrays were found to influence the voltammetric behaviours obtained. Excellent correlation was found between experimental data and theoretical predictions employing published models of microelectrode behaviour. Gold MEAs were evaluated for their applicability to copper determination in a soil extract sample, where agreement was found between the standard analytical method and a method based on underpotential deposition-anodic stripping voltammetry (UPD-ASV) at the MEAs, offering a mercury-free alternative for copper sensing.

Electrochemical detection of dopamine using arrays of liquid-liquid micro-interfaces created within micromachined silicon membranes.

The detection of protonated dopamine by differential pulse voltammetry (DPV) and square wave voltammetry (SWV) at arrays of micro-interfaces between two immiscible electrolyte solutions (microITIES) is presented. Microfabricated porous silicon membranes (consisting of eight pores, 26.6 microm in radius and 500 microm pore-pore separation, in a hexagonal layout) were prepared by photolithographic and etching procedures. The membrane pores were fabricated with hydrophobic internal walls so that the organic phase filled the pores and created the liquid interface at the aqueous side of the membrane. These were used for harnessing the benefits of three-dimensional diffusion to the interface and for interface stabilisation. The liquid-liquid interface provides a simple method to overcome the major problem in the voltammetric detection of dopamine at solid electrodes due to the co-existence of ascorbate at higher concentrations. Selectivity for dopamine over ascorbate was achieved by the use of dibenzo-18-crown-6 (DB18C6) for the facilitated ion transfer of dopamine across the microITIES array. Under these conditions, the presence of ascorbate in excess did not interfere in the detection of dopamine and the lowest concentration detectable was ca. 0.5 microM. In addition, the drawback of current signal saturation (non-linear increase of the peak current with the concentration of dopamine) observed at conventional (millimetre-sized) liquid-liquid interfaces was overcome using the microfabricated porous membranes.

Detection of food additives by voltammetry at the liquid-liquid interface.

Electrochemistry at the liquid-liquid interface enables the detection of nonredoxactive species with electroanalytical techniques. In this work, the electrochemical behavior of two food additives, aspartame and acesulfame K, was investigated. Both ions were found to undergo ion-transfer voltammetry at the liquid-liquid interface. Differential pulse voltammetry was used for the preparation of calibration curves over the concentration range of 30-350 microM with a detection limit of 30 microM. The standard addition method was applied to the determination of their concentrations in food and beverage samples such as sweeteners and sugar-free beverages. Selective electrochemically modulated liquid-liquid extraction of these species in both laboratory solutions and in beverage samples was also demonstrated. These results indicate the suitability of liquid-liquid electrochemistry as an analytical approach in food analysis.