Andrzej Bobrowski

Bismuth-film-plated carbon paste electrodes

Abstract In this preliminary note, carbon paste electrodes (CPEs) plated with a bismuth film are presented. The bismuth film can be generated onto the carbon paste surface either from an external plating solution or in situ; the latter being performed in two ways: (i) as a spike of the Bi 3+ ions to the solution or (ii) via modifying the carbon paste with solid bismuth oxide (5% m/m). As shown on selected examples, bismuth-film-plated CPEs exhibit a good performance in voltammetric stripping analysis of some heavy metals such as Pb, Cd, and Zn.

Determination of arsenic at a gold-plated carbon paste electrode using constant current stripping analysis

A new stripping method for the determination of arsenic in water samples with a gold film-plated carbon paste electrode has been developed for the use in constant current stripping analysis (CCSA). In the novelized procedure, differentiation between As(III) and chemically pre-reduced As(V), the effect of Cu(II) on the response of arsenic, and the stability of sample solutions were studied in detail. Compared to the voltammetric approach, the method utilizing CCSA offers a more rapid procedure with improved analytical characteristics such as reproducibility, selectivity over the Cu(II) ions, or lower detection limit (3 ppb for As(III) and 0.5 ppb for As(V), respectively). The possibilities of the optimized method are demonstrated by determinations of As(III), As(V), and total arsenic in samples of polluted river water.

Determination of Cobalt by Adsorptive Stripping Voltammetry Using Cobalt(II)-nioxime-nitrite Catalytic System

Abstract A differential pulse adsorptive voltammetric method for the cobalt determination with detection limit of 1.2x10−10 M (100 sec preconcentration) is proposed. The preconcentration of Co(II)-nioxime complex during the adsorption step and utilization of catalytic effect during the reduction of Co(II)-nioxime complex provides a great enhancement of cobalt voltammetric response. The ammonia buffer solution containing nioxime and nitrite is suitable for the adsorptive voltammetric determination of nanomolar cobalt concentrations in the presence of 1000-fold excess of nickel and 10 000-fold excess of zinc.

Electrochemical and Spectroscopic Investigation of the Reduction of Dimethylglyoxime at Mercury Electrodes in the Presence of Cobalt and Nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state:  Co(II) + 2dmgH(2) ⇌ (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ⇌ (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.

Application of the Bismuth Film Electrode for Catalytic Adsorptive Stripping Potentiometric Determination of Cobalt in Dimethylglyoxime‐Nitrite System

Abstract The application of bismuth film electrodes to the determination of cobalt by constant current adsorptive stripping potentiometry with exploitation of a catalytic effect is presented. The addition of NaNO2 to the solution containing ammonia buffer and dimethylglyoxime results in a 25‐fold enhancement of the adsorptive stripping potentiometric cobalt signal. Several key parameters of the potentiometric stripping mode were optimized, including the composition of the supporting electrolyte, the stripping current, the accumulation potential, and the accumulation time. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=1.4% for a Co concentration of 2 µg L−1), low detection limit (0.07 µg L−1), and good linearity (up to 10 µg L−1, R2=0.998) with a deposition time of 60 s and a stripping current of 10 µA. The method enables the determination of Co in the presence of high excesses of Ni or Zn.

On-line monitoring of cobalt ion zinc plant electrolyte by differential pulse adsorptive stripping voltammetry

Abstract Two methods that have now been used routinely for several years for on-line monitoring of cobalt in zinc plant electrolyte by adsorptive stripping voltammetry (ADSV) are described in which interference from the very high background zinc concentration is overcome. The first method combines ADSV of cobalt as its dimethylgloxime complex at a hanging mercury drop electrode with in situ matrix exchange. This method utilises a bottom-drain flow-through cell to overcome problems associated with the high density of zinc electrolyte and enables cobalt to be determined down to 9 μg 1 −1 in plant electrolyte solutions which contain 150 g 1 −1 zinc. The method is therefore suitable for low-purity electrolyte. However, in highly purified zinc electrolyte the matrix exchange technique lacks the required sensitivity for cobalt determination and a second technique known as catalytic differential pulse ADSV is employed which has a detection limit of 0.25 μg 1 −1 cobalt in zinc plant electrolyte. The catalytic technique again utilises a bottom-drain flow-cell, but involves formation of the α-benzil dioxime complex rather than that with dimethylglyoxime. Addition of nitrite enhances the cobalt signal and eliminates the need for matrix exchange. Both methods have been adapted foruse in on-line voltammetric analysers at Pasminco Metals-EZ. The condition used for efficient removal of cobalt during the purification process almost invariably result in removal of nickel to levels where possible interference from the presence of high nickel concentrations does not occur in the practical situation.

Adsorptive voltammetric determination of copper as its nioximate complex

A sensitive and selective stripping voltammetric ultratrace determination of copper is described, based on adsorptive accumulation of the cu(II)-nioxime complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The analytical conditions for the determination of copper by differential-pulse and linear-scan absorption voltammetry have been optimized. The method is compared to the routine anodic stripping voltammetric method for copper. Its applicability to river and potable water analysis is illustrated. The detection limit, restricted by the blank, is about 0.5 microg/l.; the relative standard deviation (at microg/l. level) for a standard solution is below 5% and for water samples is 5-9%.

Renewable silver amalgam film electrodes in electrochemical stripping analysis-a review

The success of a voltammetric sensing procedure depends mainly on the proper choice of the working electrode. This is because its ability to accumulate the analyte determines the sensitivity of the method. The main criterion of the selection of the proper working electrode is the available potential window. A variety of conductive materials have been used for the preparation of working electrodes. Of these, two kinds of mercury electrodes—hanging mercury drop and film—were used because of their excellent voltammetric performance and, in particular, their high overpotential of hydrogen reduction. The significant drawbacks of mercury electrodes, however, are the toxicity of the material and the instability of liquid mercury films. To overcome these disadvantages, less toxic mercury-containing materials have been used, such as amalgams and amalgam film electrodes. This group includes renewable silver amalgam film electrodes used for electrochemical stripping sensing purposes. These electrodes have successfully been applied for anodic, adsorptive, cathodic, catalytic voltammetric, and potentiometric stripping determination of trace amounts of inorganic cations and organic compounds in various natural matrices. In this review, the electrode design, characteristics, and application of two kinds of renewable silver amalgam film electrodes are discussed in detail.

Application of catalytic adsorptive stripping voltammetry of the cobalt-α-benzil dioxime complex to analysis of cobalt traces in metallic zinc

The catalytic adsorptive stripping voltammetric method with alpha-benzil dioxime and nitrite affords numerous advantages in cobalt determination. The detailed conditions of the determination of the cobalt traces in metallic zinc by catalytic adsorptive stripping voltammetry have been investigated. Both the linear sweep and the differential pulse stripping modes can be used with similar sensitivity. Possible interferences by Mn, Pb, Cu, Ni and Fe are evaluated. In the presence of 5 x 10(5) fold excess of Zn the linear dependence of the cobalt CASV peak current on concentration ranged from 0.05 mug/l to 3 mug/l. Optimal conditions include the accumulation potential of -0.65 V and the accumulation time of 10 sec. The results of the determination of 10(-5)% level of Co in the metallic zinc showed good reproducibility (relative standard deviation, RSD = 0.07) and reliability.

Determination of Copper(II) Through Anodic Stripping Voltammetry in Tartrate Buffer Using an Antimony Film Screen-printed Carbon Electrode

ABSTRACT The voltammetric performance of an in situ plated antimony film screen-printed carbon electrode in hydrochloric acid, acetate buffer, and tartrate buffer was evaluated for the detection of copper(II) with differential pulse anodic stripping voltammetry. The tartrate buffer was superior, providing high sensitivity and good separation of copper and antimony stripping peaks. The analytical conditions for the determination of copper(II) were optimized. The detection limit was estimated to be 0.14 µg L−1 copper(II) and the relative standard deviation for 2.5 µg L−1 copper(II) was 3%. The applicability of the method was illustrated by the analysis of soil conditioner samples.