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Abstract: This paper describes the fabrication of band electrodes and electrode arrays recessed within nanoscale trenches sculpted in silicon nitride passivation layers by focused ion beam (FIB) milling, thus creating recessed nanoband electrodes. Controllable nanoband dimensions, numbers and inter-band spacing have been rapidly created by the direct write approach of the FIB milling technique. Milling of cross-sections through the trenches demonstrated that the trench walls were non-vertical and enabled evaluation of the trench wall angle, ca. 19°. Cyclic voltammetric characterisation using a simple redox probe ion, ferrocene carboxylate in phosphate buffered saline electrolyte solution, demonstrated steady-state voltammetric curves, consistent with multi-dimensional diffusion being the controlling mass transport mechanism under these conditions. The simplicity of the preparation method for these nanoband devices provides scope for their use in sensing applications as well as in fluid transport studies in nanodimensions. [Copyright &y& Elsevier]

Abstract: We introduce the behaviour and applications of underpotential deposition (UPD) and its combination with stripping voltammetry (UPD–SV) of metal analytes at solid-electrode surfaces as an important analytical strategy for trace-metal determinations. We review the principles of UPD together with model metal/electrode systems, and discuss analytical utility, including achievement of limits of detection (LODs) and applications to a variety of sample matrices. We present an approach to the alleviation of sample-matrix effects by using surface-protective disorganised monolayer coatings. Finally, we also present the outlook for UPD–SV as an electroanalytical tool. [Copyright &y& Elsevier]

Reports on the development of an approach for the prevention of electrode surface fouling by surfactants. Use of spontaneously adsorbed monolayer systems to form porous disorganized monolayer of gold electrodes; Anodic stripping of underpotential deposits; Sample application in copper detection.

The development of mercury-free electroanalytical systems for in-field analysis of pollutants requires a foundation on the electrochemical behaviour of the chosen electrode material in the target sample matrices. In this work, the behaviour of gold working electrodes in the media employed in the BCR sequential extraction protocol, for the fractionation of metals in solid environmental matrices, is reported. All three of the BCR sequential extraction media are redox active, on the basis of acidity and oxygen content as well as the inherent reducing or oxidising nature of some of the reagents employed: 0.11 M acetic acid, 0.1 M hydroxylammonium chloride (adjusted to pH 2) and 1 M ammonium acetate (adjusted to pH 2) with added trace hydrogen peroxide. The available potential ranges together with the demonstrated detection of target metals in these media are presented. Stripping voltammetry of copper or lead in the BCR extract media solutions reveal a multi-peak behaviour due to the stripping of both bulk metal and underpotential metal deposits. A procedure based on underpotential deposition–stripping voltammetry (UPD-SV) was evaluated for application to determination of copper in 0.11 M acetic acid soil extracts. A preliminary screening step in which different deposition times are applied to the sample enables a deposition time commensurate with UPD-SV to be selected so that no bulk deposition or stripping occurs thus simplifying the shape and features of the resulting voltammograms. Choice of the suitable deposition time is then followed by standards addition calibration. The method was validated by the analysis of a number of BCR 0.11 M acetic acid soil extracts. Good agreement was obtained been the UPD-SV method and atomic spectroscopic results. [Copyright &y& Elsevier]

Abstract: A microfluidic device with integrated electrodes for the electrochemically-modulated extraction of ions across immiscible aqueous–organic liquid–liquid interfaces is presented. Using a Y-shaped microfluidic channel with in situ electrodes and co-flowing aqueous and organic immiscible electrolyte solutions, the manipulation of the applied interfacial potential enabled the extraction of ions from the aqueous phase into the organic phase. Data for the extraction of tetraethylammonium cations from aqueous electrolyte into 1,2-dichloroethane electrolyte are presented. The device demonstrates the benefits of combination of microfluidics and liquid–liquid electrochemistry. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-N′-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-(N′-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO4 2− in the concentration range 5.0×10−5 to 1.0×10−1 M, with near-Nernstian response slopes of −33.0 and −28.0mVdec−1 for ionophores I and II, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO4 2− with respect to the other anions, including sulfate and nitrate. [Copyright &y& Elsevier]

Electrochemical measurements were undertaken for the investigation of the underpotential deposition-stripping process of copper at bare and modified gold electrodes in 0.11 M acetic acid, the first fraction of the European Union’s Bureau Communautaire de Références (BCR) sequential extraction procedure for fractionating metals within soils and sediments. Gold electrodes modified with mercaptoacetic acid showed higher sensitivity for the detection of copper than bare gold electrodes, both in the absence and in the presence of humic acid in acetic acid solutions, using the underpotential deposition-stripping voltammetry (UPD-SV) method. In the presence of 50 mg l-1 of humic acid, the mercaptoacetic acid modified electrode proved to be 1.5 times more sensitive than the bare gold electrode. The mercaptoacetic acid monolayer formed on the gold surface provided efficient protection against the adsorption of humic acid onto the gold electrode surface. Variation of the humic acid concentration in the solution showed little effect on the copper stripping signal at the modified electrode. UPD-SV at the modified electrode was applied to the analysis of soil extract samples. Linear correlation of the electrochemical results with atomic spectroscopic results yielded the straight-line equation y (μg l-1) = 1.10x - 44 (ppb) (R=0.992, n=6), indicating good agreement between the two methods. [Copyright &y& Elsevier]