Malgorzata Grabarczyk

Determination of uranium by adsorptive stripping voltammetry at a lead film electrode.

An adsorptive stripping voltammetric procedure for the determination of U(VI) at an in situ plated lead film electrode is described. The U(VI) complex with cupferron was accumulated from an acetate buffer solution of pH 4.2 at the potential -0.65V. The measurements were carried out from undeaerated solutions. The calibration graph for an accumulation time of 180s was linear from 5x10(-10) to 2x10(-8)molL(-1). The detection limit was 2x10(-10)molL(-1), the relative standard deviation for 2x10(-8)molL(-1) U(VI) was 4.3%. The proposed procedure was validated in the course of U(VI) determination in water certified reference materials.

Development of a simple and fast voltammetric procedure for determination of trace quantity of Se(IV) in natural lake and river water samples.

A simple and fast cathodic stripping voltammetric procedure for determination of trace quantity of Se(IV) in natural samples containing high concentrations of surfactants and humic substances was developed. The procedure exploiting selenium accumulation (from sample solution spiked with 0.1 mol L(-1) HClO(4) and 4 x 10(-4)mol L(-1) Cu(NO(3))(2)) as Cu(2)Se was employed as the initial method. The deposited Cu(2)Se was stripped by differential pulse cathodic potential scan. The interference from dissolved organic matter such as surfactants and humic substances was eliminated by adding Amberlite XAD-7 resin to the voltammetric cell. The whole procedure was applied to a single cell, which allows one to monitor the voltammetric scan. Optimum conditions for removing the surfactants and humic substances due to their adsorption on XAD-7 resin were evaluated. The method was tested on synthetic samples spiked with surfactants and humic substances. The calibration graph for Se(IV) under optimized conditions following the accumulation of 30s was linear in the range from 2 x 10(-9) to 2 x 10(-7)mol L(-1) and was found to obey the equation y=0.74x-0.61, where y and x are the peak current (nA) and Se(IV) concentration (nmol L(-1)), respectively. The linear correlation coefficient was r=0.9993. The relative standard deviation for determination of Se(IV) at the concentration of 1 x 10(-8)mol L(-1) was 3.7% (n=5). The detection limit estimated from three times the standard deviation for low Se(IV) concentration and accumulation time of 30s was about 7.8 x 10(-10)mol L(-1). The presented procedure was successfully applied to selenium determination in TMRAIN-95 certified reference material and to real samples including spiked lake and river waters for selenium speciation.

Application of gallium film electrode for elimination of copper interference in anodic stripping voltammetry of zinc

For elimination of copper interference in anodic stripping determinations of zinc at mercury and bismuth film electrodes gallium ions are usually added to the supporting electrolyte. In the presented studies novel ex situ formed gallium film electrode was applied for this purpose. The proposed electrode is less toxic than mercury one while the detection limit for zinc was lower than for bismuth film electrode following the same deposition time. The calibration graph for deposition time of 60s was linear from 5x10(-8) to 2x10(-6)mol L(-1). The determinations of zinc were carried out from undeaerated solutions. The proposed procedure was applied to zinc determination in certified reference material and tap water sample.

Voltammetric determination of traces of Cr(VI) in the flow system in the presence of bipyridyne.

The voltammetric method of Cr(VI) determinations in the flow system, based on the combination of selective accumulation of the product of Cr(VI) reduction on HMDE and a very sensitive method of chromium determination in the presence of bipyridine [Z. Gao K.S. Siow, Electroanalysis 8 (1996) 602] is proposed. The calibration graphs were linear from 3x10(-9) to 3x10(-8) and from 5x10(-10) to 5x10(-9) mol l(-1) for accumulation times 120 and 600 s, respectively. The relative standard deviation (R.S.D.) was 6.5% (n=5) for Cr(VI) concentration 1x10(-8) mol l(-1) and the accumulation time 120 s. The influence of foreign ions commonly present in water samples is presented. Validation of the method was made by comparison of the results of analyses of tap water by another electrochemical method and by recovery test for river and mineral water.

Evaluation of ammonia buffer containing EDTA as an extractant for Cr(VI) from solid samples

A novel procedure for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from solid samples was presented. EDTA was added to an ammonia buffer commonly used only for the extraction of soluble and sparingly soluble Cr(VI). In the course of extraction in an ultrasonic bath cations which form insoluble chromates are complexed with EDTA while Cr(VI) is transferred to the solution. A concentration of EDTA equal to 0.01molL(-1) was chosen. The presence of EDTA in the extraction solution enables not only dissolution of insoluble Cr(VI) but also, as reported previously in literature, minimises oxidation of Cr(III) to Cr(VI). The extraction procedure was optimised and applied to Cr(VI) determination in the paint chips real sample. The results obtained were compared with the results obtained using two other extraction procedures. The results show that the novel extraction procedure can be used for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from real solid samples.

Determination of Cr(VI) in the presence of Cr(III) and humic acid by cathodic stripping voltammetry

Abstract A voltammetric procedure in the flow system for determination of traces of Cr(VI) in the presence of Cr(III) and humic acid is presented. The calibration graph is linear from 5×10−10 to 1×10−7 mol l−1 for an accumulation time of 120 s. The R.S.D. for 1×10−8 mol l−1 Cr(VI) is 5.3% (n=5). The detection limit estimated from 3σ for a low concentration of Cr(VI) and accumulation time of 120 s is 2×10−10 mol l−1. The method can be used for Cr(VI) determination in the presence of up to 50 mg l−1 of humic acid. The validation of the method was carried out by studying the recovery of Cr(VI) from spiked river water and by the comparison of the results of determination of Cr(VI) in a soil sample. The method cannot be used for analysis of samples containing high concentrations of chloride ions such as seawater and estuarine water.

An adsorptive stripping voltammetry procedure for ultra-trace determination of U(VI) using double accumulation step on two lead-film working electrodes

We report a very sensitive stripping voltammetric procedure for determination of ultra-trace quantity of U(VI) in water samples. A very low detection limit was achieved owing to the application of a new construction of the voltammetric electrode cell with two built-in working electrodes that differed significantly in their surface area. The procedure was based on the double adsorptive accumulation of the U(VI)-cupferron complex onto two lead film working electrodes. Under optimal conditions the detection limit for accumulation time of 120 s for the big electrode and 120 s for the small electrode was about 3.1 × 10(-11) mol L(-1), whereas for accumulation time of 480 s for the big electrode and 240 s for the small electrode it was about 1.1 × 10(-11) mol L(-1). The proposed method was successfully validated using certified reference material seawater NASS-5.

A new voltammetric strategy for sensitive and selective determination of gallium using cupferron as a complexing agent

This article describes a differential pulse adsorptive stripping voltammetric method for the trace determination of gallium in environmental water samples. It is based on the adsorptive deposition of the complex Ga(III)-cupferron at the hanging mercury drop electrode (HMDE) at −0.4 V (versus Ag/AgCl) and its cathodic stripping during the potential scan. The method was optimized as concerns the main electrochemical parameters that affect the voltammetric determination (supporting electrolyte, pH, cupferron concentration, deposition potential and time). The calibration graph is linear from 5 × 10−10 to 5 × 10−7 mol L−1 with a detection limit calculated as 1.3 × 10−10 mol L−1 for deposition time of 30 s. The influence of interfering substances such as surfactants and humic substances present in the matrices of natural water samples on the Ga(III) signal was examined and a satisfying minimization of these interferences was proposed. The procedure was applied to direct determination of gallium in environmental water samples.

Selective, sensitive and economical method for the adsorptive voltammetric determination of trace amounts of Mo(VI) in organic matter rich environmental samples

A differential pulse adsorptive stripping voltammetric method has been developed for molybdenum trace determination in environmental water samples containing organic compounds. It was proved that interferences from the organic matrix such as surface active substances and humic substances could be removed by the addition of resin to the analysed sample prior to voltammetric measurement. The parameters for Mo(VI) determination in the presence of resin, using a hanging mercury drop as the working electrode, were examined systematically for two complexing agents: cupferron and chloranilic acid. The detection limits estimated from 3 times the standard deviation for a low Mo(VI) concentrations were equal to 5 × 10(-11) and 3 × 10(-10) mol L(-1) for cupferron and chloranilic acid, respectively. At the optimized conditions the quantitative Mo(VI) determination in the presence of even 50 mg L(-1) of surface active compounds can be performed. The proposed procedures were validated in the course of Mo(VI) determination in certified reference material NASS-5 and in the course of studying recovery of Mo(VI) from spiked river water samples.

Determination of trace amounts of Ga(III) by adsorptive stripping voltammetry with in situ plated bismuth film electrode.

The determination of trace gallium using adsorptive stripping voltammetry at an in situ plated bismuth film electrode was described. The method was based on simultaneous film formation and the Ga(III)-cupferron complex preconcentration at -0.65 V and its cathodic stripping during the potential scan. The effect of Bi(III) and cupferron concentration, the influence of deposition potential and time, and the scan rate on the determination of Ga(III) were studied. A linear response in the concentration range of 3×10(-10) to 3×10(-7) mol L(-1) (r=0.998) was obtained with detection limit of 1.05×10(-10) mol L(-1) using accumulation time of 180 s. Finally, the bismuth film electrode was successfully applied for the determination of Ga(III) in certified reference material seawater NASS-5 with satisfactory results.