Mieczyslaw Korolczuk

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.

Voltammetric method for the determination of sildenafil citrate (Viagra) in pure form and in pharmaceutical formulations

A highly sensitive and simple voltammetric method for the determination of sildenafil citrate (SC) was developed. The method is based on the accumulation by adsorption of SC on a lead film modified glassy carbon electrode (LF/GCE) and then the reduction of SC throughout the stripping step. During the determinations of SC at the lead film electrode three adsorptive stripping voltammetric peaks at -1.2, -1.33 and -1.45V were observed. The respective response selected for identification and quantification has been evaluated with respect to the composition and pH of the supporting electrolyte, the potential and the time of the lead film formation, the potential and the time of the SC accumulation and other variables. Experimental results indicate an excellent linear correlation between the peak current and concentration in the range of 2x10(-9)-1.5x10(-7)mol/L (for peaks 1 and 2) and 1x10(-8)-1.5x10(-7)mol/L (for the peak 3). The detection limits (LOD) for SC following 30s of accumulation time were equal to 9x10(-10)mol/L (for peaks 1 and 2) and 4.5x10(-9)mol/L (for the peak 3). The method was successfully applied to the determination of SC in the tablets (Viagra 25 and Viagra 50) and average the contents were in close agreement with those quoted by the manufacturer and with those obtained by the reported spectrophotometric method and voltammetric method using a hanging mercury drop electrode.

Adsorptive stripping voltammetric determination of trace concentrations of molybdenum at an in situ plated lead film electrode.

An in situ plated lead film electrode has been applied for adsorptive stripping voltammetric determination of trace concentrations of molybdenum in the presence of Alizarin S. The procedure is based on the preconcentration of the molybdenum-Alizarin S complex at an in situ plated lead film electrode held at -0.6 V (versus Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The peak current is proportional to the concentration of molybdenum over the range 2x10(-9) to 5x10(-8) mol L(-1), with a 3sigma detection limit of 9x10(-10) mol L(-1) with an accumulation time of 60 s. The measurements were carried out from underaerated solutions. The proposed procedure was validated in the course of Mo(VI) determination in water certified reference materials.

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 method for direct determination of nickel in natural waters in the presence of surfactants.

Voltammetric procedures for direct Ni(II) determination in natural water samples are described. The procedures are based on nickel deposition to the metallic state and then its oxidation in the presence of dimethylglyoxime with the formation of the complex adsorbed on the electrode. Reduction of the complex is exploited in the detection step. Due to the application of a sufficiently negative deposition potential the interference from surfactants is minimized. The detection limits for Ni(II) are 2x10(-9) and 2x10(-10) mol l(-1) for deposition times of 30 and 120 s, respectively. The influence of foreign ions is also presented.

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.