Effect of Temperature on the Removal of Interferences in the Voltammetric Procedure for the Determination of Cr(VI)

The aim of this paper was to investigate the effect of temperature on the removal efficiency of surfactant-induced interferences. Surfactants were removed as a result of mixing with XAD-7 resin. The study was carried out using the example of Cr(VI) determination by adsorption stripping voltammetry (AdSV). Measurements were carried out using a solution containing Cr(VI), acetate buffer (pH = 6.2), DTPA, KNO3, and different surfactants. Ten mL of the solution was mixed with 0.5 g of XAD-7 resin at different temperatures for 5 min prior to voltammetric measurement. The effect of the mixing temperature of the sample with the resin on the voltammetric Cr(VI) signal in the presence of different surfactants was studied in the range from 20 to 60 °C. The proposed method of removing interference from surfactants by mixing the sample with the XAD-7 resin at 60 °C was used for the determination of trace amounts of Cr(VI) in river water containing non-ionic, anionic, cationic surfactants, and biosurfactants.

Adsorptive Stripping Voltammetry for Determination of Vanadium: A Review

The main purpose of this review is to present methods of adsorptive stripping voltammetry that can be used to determine trace amounts of VO₂⁽⁺⁾ in various types of samples. The detection limits achieved using different working electrodes are presented. The factors influencing the obtained signal, including the selection of the complexing agent and the selection of the working electrode, are shown. For some methods, in order to increase the range of applied concentrations in which vanadium can be detected, a catalytic effect is introduced to adsorptive stripping voltammetry. The influence of the foreign ions and organic matter contained in natural samples on the vanadium signal is analyzed. This paper presents methods of elimination associated with the presence of surfactants in the samples. The methods of adsorptive stripping voltammetry for the simultaneous determination of vanadium with other metal ions are also characterized below. Finally, the practical use of the developed procedures, mainly for the analysis of food and environmental samples, is summarized in a tabular version.

The Use of a Solid Bismuth Microelectrode for Vanadium Quantification by Adsorptive Stripping Voltammetry in Environmental Water Samples

This paper presents for the first time the use of an environmentally friendly solid bismuth microelectrode for the voltammetric quantification of V(V) in natural water samples. These studies were designed to replace the film bismuth electrode that had been introduced to eliminate the conventional sensors based on highly toxic mercury. In the proposed procedure, V(V) is preconcentrated at the solid bismuth microelectrode surface via the formation of electroactive complexes with cupferron from a solution of 0.1-mol L⁻¹ acetate buffer, pH = 4.6 at a potential of −0.4 V. The linearity of the calibration graph is in the V(V) concentration range from 8 × 10⁻¹⁰ to 1 × 10⁻⁷ mol L⁻¹ with a preconcentration time of 1 min. The limit of detection (calculated as 3 σ) is 2.5 × 10⁻¹⁰ mol L⁻¹ for a preconcentration time of 1 min. It was also demonstrated that significant improvement in analytical parameters was achieved as a result of the activation of the solid electrode surface at a potential of −2.5 V for 2 s. The developed procedure is highly selective for the presence of foreign ions and organic compounds in tested samples. The accuracy of the recommended procedure was checked using SPS-WW1 waste water-certified reference materials of a complex composition, in which the concentration of V(V) determined by the proposed method was 95.1 ± 1.6 ng mL⁻¹. Moreover, in keeping with the outlined procedure, river, tap and rain water samples were analyzed without any pretreatment, and recovery values from 96% to 106% were obtained.

Sensitive detection of molybdenum through its catalysis and quenching of gold nanocluster fluorescence

Molybdenum (Mo) is an essential nutrient for the proper functioning of some enzymes in living organisms as human beings. Conventional methods for its detection require complicated instrumentations as atomic absorption or mass spectrometers. In this work, a sensitive kinetic fluorescence was developed as an alternative. Gold nanoclusters (AuNCs) with red fluorescence emission were synthesized, and this fluorescence was effectively quenched by iodine through an etching process. It was found that the presence of Mo significantly speeded up a reaction for the generation of iodine, and thus enhanced the quenching. This effect was then adopted for the development of a sensitive fluorescent measurement toward Mo. The method was capable of detecting Mo down to 0.2 nM and was successfully applied for the analyses of mung bean and tea leaf samples.

Trace vanadium analysis by catalytic adsorptive stripping voltammetry using mercury-coated micro-wire and polystyrene-coated bismuth film electrodes

An electrochemical technique has been developed for ultra-trace (ng L(-1)) vanadium (V) measurement. Catalytic adsorptive stripping voltammetry for V analysis was developed at mercury-coated gold micro-wire electrodes (MWEs, 100 microm) in the presence of gallic acid (GA) and bromate ion. A potential of -0.275 V (vs Ag/AgCl) was used to accumulate the complex in acetate buffer (pH 5.0) at the electrode surface followed by a differential pulse voltammetric scan. Parameters affecting the electrochemical response, including pH, concentration of GA and bromate, deposition potential and time have been optimized. Linear response was obtained in the 0-1000 ng L(-1) range (2 min deposition), with a detection limit of 0.88 ng L(-1). The method was validated by comparison of results for an unknown solution of V by atomic absorption measurement. The protocol was evaluated in a real sample by measuring the amount of V in river water samples. Thick bismuth film electrodes with protective polystyrene films have also been made and evaluated as a mercury free alternative. However, ng L(-1) level detection was only attainable with extended (10 min) deposition times. The proposed use of MWEs for the detection of V is sensitive enough for future use to test V concentration in biological fluids treated by the advanced oxidation process (AOP).