A Decade with Bismuth-Based Electrodes in Electroanalysis

Trace lead analysis based on carbon-screen-printed-electrodes modified via 4-carboxy-phenyl diazonium salt electroreduction

This paper describes the use of 4-carboxyphenyl-grafted screen-printed carbon electrodes (4-CP-SPEs) for trace lead analysis. These novel and simple use of electrodes were easily prepared by the electrochemical reduction of the corresponding diazonium salt. Pb detection was then performed by a three-steps method in order to avoid oxygen interference: (i) immersion of the grafted screen-printed electrode (SPE) in the sample and adsorption of Pb(II), (ii) reduction of adsorbed Pb(II) by chronoamperometry (CA), and (iii) oxidation of Pb by Anodic Square Wave Voltammetry (SWV). The reoxidation response was exploited for lead detection and quantification. In order to optimize the analytical responses, the influence of the adsorption medium pH and the adsorption time were investigated. Moreover, an interference study was carried out with Cu(II), Hg(II), Al(III), Mn(II), Zn(II), Cd(II) and no major interference can be expected to quantify Pb(II). The described method provided a limit of detection and a limit of quantification of 1.2 × 10(-9)M and 4.1 × 10(-9)M, respectively. These performances indicate that the 4-CP-SPE could be considered as an efficient tool for environmental analysis.

Polarimetric characterization of bismuth thin films deposited by laser ablation

A Mueller-Stokes analysis is applied to pure bismuth thin film samples prepared by the laser ablation technique by using a polarimeter with a 632.8 nm continuum wavelength laser. The complex refractive index is determined in the range of 250-1100 nm. Results from the Mueller matrix show the high sensitivity of diattenuation and polarizance parameters as a function of the sample thickness and the incidence angle, except at the pseudo-Brewster angle, where they exhibit the same value. Results show that the knowledge of the polarimetric response, with appropriate incident polarization states, could be used to design photonic Bi-based devices for several applications. Polarization dependence is the result of changes on the surface morphology as a result of the small value of the skin depth.

Computer-controlled fluid-flow chemical analysis (CC-FCA) and its application to environmental analytical chemistry

Computer-controlled fluid-flow chemical analysis (CC-FCA) was investigated for the determination of trace amounts of toxic pollutants in the environment. For CC-FCA, automated chemical analysis systems were developed by using computer-controllable pumping and valve modules, and polytetrafluorethylene (PTFE) tubing and connectors. The systems demonstrated in this work were a flow injection-type system, a sequential injection-type system, a mini-column pretreatment system (Auto-Pret system), and an Auto-Pret hyphenated with flow injection analysis (FIA) system. Such systems were fully controlled by a computer program; the lab-made programs were written in Visual Basic. The systems can be hyphenated with some detectors, such as a spectrophotometric detector, an electrochemical detector, electrothermal-atomic absorption spectrometry (ET-AAS), a liquid electrode plasma-atomic emission spectrometry (LEP-AES) and inductively coupled plasma (ICP)-AES. Such systems were successfully applied to the determination of trace amounts of toxic pollutants in environmental water samples: they were heavy metal ions (Pb, Cd, Cr, etc.). In this paper, the author aims mainly at investigating the CC-FCA method for the determination of trace amounts of Cr(VI) in environmental water samples by spectrophotometry. The techniques used in this work were FIA, sequential injection analysis (SIA), and Auto-Pret/FIA, which were all computer-controllable. Limits of detection of Cr(VI) by FIA, SIA, and Auto-Pret/FIA were 8 × 10–9 mol/L (0.4 μg/L), 1.1 × 10–8 mol/L (0.6 μg/L), and 1.4 × 10–9 (0.07 μg/L), respectively. The methods were applied to the determination of Cr(VI) in river and drinking waters.

Cathodic electrochemiluminescence and reversible electrochemistry of [Ru(bpy)3](2+/1+) in aqueous solutions on tricresyl phosphate-based carbon paste electrode with extremely high hydrogen evolution potential

Many cathodic electrochemiluminescence (ECL) systems require very negative potentials; it is difficult to achieve stable cathodic ECL in aqueous solutions because of hydrogen evolution and instability of intermediates. In this study, tricresyl phosphate-based carbon paste electrode (CPE) was used to achieve cathodic ECL. It exhibits no obvious hydrogen evolution even at a potential up to -1.6 V and dramatically stabilizes electrogenerated [Ru(bpy)3](+). Therefore, a reversible wave of [Ru(bpy)3](2+/1+) in aqueous solutions at carbon electrode has been observed for the first time, and cathodic ECL of [Ru(bpy)3](2+)/S2O8(2-) has been achieved. Under the optimum conditions, the plots of the ECL versus the concentration of S2O8(2-) are linear in the range of 10(-6) to 10(-2) M with the detection limit of 3.98 × 10(-7) M. Common anions have no effect on the ECL intensity of the [Ru(bpy)3](2+)/S2O8(2-) system. Since CPEs have been widely used, CPEs with high hydrogen evolution potential are versatile platforms for electrochemical study and cathodic ECL study.

Evaluation of trace heavy metal levels in soil samples using an ionic liquid modified carbon paste electrode

An ionic liquid n-octylpyridinium hexafluorophosphate (OPFP) modified carbon paste electrode was developed. This ionic liquid modified carbon electrode showed better electrochemical activities compared with the traditional carbon paste electrode which employed the paraffin oil as the binder. With the electrochemically deposited bismuth film, the developed electrode exhibited well-defined and separate stripping voltammetric peaks for cadmium and lead. The linear range of the bismuth film electrode was from 1.0 μg L(-1) to 100.0 μg L(-1) for both metal ions with a deposition time of 120 s and a deposition potential of -1.2 V in pH 4.5 acetate buffer solution. The detection limit was 0.10 μg L(-1) for cadmium and 0.12 μg L(-1) for lead with a deposition time of 180 s. The electrode was also applied to determine cadmium and lead in soil sample extracts. Results suggested that the proposed electrode was sensitive, reliable and effective for the determination of trace heavy metals.