The cathodic stripping voltammetric determination of traces of iodide with a hanging copper amalgam drop electrode

A hanging copper amalgam drop electrode (HCADE) is used for the determination of traces of iodide by cathodic stripping voltammetry. The cathodic stripping peak of copper(I) iodide from the HCADE is better defined than that of mercury(I) iodide from a hanging mercury drop electrode. Optimum conditions and interferences are reported. With a 3-min deposition time at ?0.1 V vs. SCE, the calibration plot is linear up to 2 × 10^?6 mol dm^?3 iodide. The detection limit for iodide with the HCADE under voltammetric conditions is 4 × 10^?8 mol dm^?3; this is lowered to 8 × 10^?9 mol dm^?3 by using the differential pulse stripping technique.     

Iodimetric determination of hydrazine and hydroquinone with thallium(III) solutions

SeIenium(IV) at trace levels can be determined in hydrochloric and perchloric acid solutions by alternating current and differential pulse polarography. The use of a hanging mercury drop electrode with accumulation of elemental selenium followed by cathodic stripping gives detection limits in the range 0.1–1 p.p.b. With a dropping mercury electrode the detection limit is 8 p.p.b. The possible interferences of Te(IV), Ge(IV), Cu(II), Cd(II) and Pb(II) are discussed. The serious interference of lead(II) can be prevented by addition of EDTA.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.     

Electrochemical methods for monitoring of environmental carcinogens

The use of modern electroanalytical techniques, namely differential pulse polarography, differential pulse voltammetry on hanging mercury drop electrode or carbon paste electrode, adsorptive stripping voltammetry and high performance liquid chromatography with electrochemical detection for the determination of trace amounts of carcinogenic N-nitroso compounds, azo compounds, heterocyclic compounds, nitrated polycyclic aromatic hydrocarbons and aromatic and heterocyclic amines is discussed. Scope and limitations of these methods are described and some practical applications based on their combination with liquid-liquid or solid phase extraction are given.     

Voltammetric Determination of Phenylglyoxylic Acid in Urine Using Graphite Composite Electrode

A composite electrode prepared from graphite powder and epoxy resin was applied as a working electrode for the determination of phenylglyoxylic acid (one of the metabolites of styrene) in human urine. Cathodic differential pulse stripping voltammetry was used and optimum conditions have been found giving the limit of determination about 5 mg L^?1. All results were compared with those obtained using hanging mercury drop electrode. For the confirmation of suggested mechanism of the electrochemical reaction the elimination voltammetry with linear scan was used.     

An electroanalytical study of the anticancer drug dacarbazine

The electrochemical behaviour of dacarbazine [5-(3,3-dimethyl-1-triazenyl) imidazole-4-carboxamide; DTIC] was investigated by Tast and differential pulse polarography (d.p.p.) at the dropping mercury electrode, by cyclic and differential pulse voltammetry at the hanging mercury drop electrode and by anodic voltammetry at the glassy carbon electrode. Calibration graphs were obtained for 2×10^?8?2×10^?5 M DTIC by d.p.p., for 5×10^?9?1×10^?5 M by adsorptive stripping voltammetry ar a hanging mercury drop electrode, and for 1?10×10^?5 M by high-performance liquid chromatography with oxidative amperometric detection at a glassy carbon electrode. The methods are compared and applied to determine DTIC added to blood serum after a simple clean-up procedure.     

Voltammetric determination of Cr(III) in plating baths containing Cr(III) salts as the main component

The differential pulse single-sweep voltammetric technique with hanging mercury drop electrode was used for the determination of Cr(III). The determination was carried out in 0.2 mol/l sodium acetate as supporting electrolyte. The reduction peak of Cr(III) was recorded at –1.5 V vs. Ag/AgCl reference electrode. The relative standard deviation was 3% for Cr concentrations in the range of 0.4 mol/l. The determination of impurities (Cd, Cu, Pb and Zn) in fresh and overworked galvanic baths using anodic stripping voltammetry in the differential pulse mode is also described.     

Differential pulse polarography and voltammetry with a microprocessor-controlled polarograph and a pressurized mercury electrode

The performance of a microprocessor-controlled polarograph with a pressurized mercury electrode system has been evaluated. For the technique of differential pulse polarography, the theory applying to the pressurized mercury electrode in the dropping mercury format is shown to be the same as for a conventional gravity-controlled mercury electrode system. At the short drop times used (0.2–0.4 s), faradaic distortion terms are shown to influence the shape of the observed differential pulse polarograms. A substantial decrease in sensitivity is also incurred in using these short drop times, compared with the longer ones generally employed in differential pulse polarography. Results for differential pulse anodic stripping conform to the usual expectations.     

Voltammetric studies of a psychotropic drug with nitro groups. Determination of flunitrazepam in urine using HMDE

The adsorption behaviour of flunitrazepam at the hanging mercury drop electrode was studied by staircase voltammetry and by adsorptive stripping differential pulse voltammetry. Flunitrazepam is adsorbed in the whole potential range, from the most positive values up to the reduction potential. Flunitrazepam reduction product is also adsorbed. The time dependence of the voltammetric response proves that a diffusion-controlled adsorption takes place. Flunitrazepam can be determined (down to nanomolar levels) by using adsorptive preconcentration prior to the differential pulse voltammetric scan. An application of such a method to flunitrazepam determination in human urine is described. The detection limit was 30 ng per milliliter of urine with a 20-sec accumulation time; the mean relative standard deviation was lower than 3.2% and the mean recovery 97.8%.     

Comparison of fundamental and second-harmonic a.c., and normal,derivative and differential pulse linear-sweep and stripping voltammetric methods

Linear-sweep and stripping a.c. and pulse voltammetric methods have been compared for a variety of electrodes and electrode processes. Each of the linear-sweep techniques is readily used systematically because, in contrast to d.c. linear-sweep voltammetry, the theory for reversible electrode processes is basically analogous to that for polarography at a dropping mercury electrode. In stripping analysis, some departures are found at a hanging mercury drop electrode because of spherical diffusion effects. For reversible electrode processes, the limits of detection for a.c. and pulse methods are comparable. However, a.c. methods offer advantages over pulse methods in discriminating against irreversible electrode processes and permit the ready use of faster scan rates. Pulse methods are more sensitive for irreversible electrode process. Normal pulse polarography is particularly favourable in minimizing undesirable phenomena arising from adsorption or deposition of material on electrodes.     

Differential pulse anodic stripping voltammetry of lead (lI) benzoylacetonate in chloroform: Application to the analysis of free-lead gasoline and gas oil samples

The voltammetric characteristics of lead(II) benzoylacetonate in chloroform at the mercury electrode are investigated. The conditions for nearly reversible reduction of lead(II) were optimized. Anodic stripping voltammetry for the determination of trace-lead was developed using differential pulse technique to strip amalgamed lead from hanging mercury drop electrode. The experimental conditions, such as scanning rate of electrode potential and deposition time of lead were optimized. The calibration graph was linear over concentration range 5x10(-8)-10(-6) M of lead(II). The detection limit was 2.5x10(-9) and the relative standard deviation for the determination of 4x10(-7) M Pb(II) was 2%. Preceded by decomposition of organolead compounds with concentrated nitric acid, then ashing at 300 degrees C and a solvent extraction of Pb(II) benzoylacetonate in chloroform, the suitability of the proposed method for the determination of lead in free-lead gasoline and gas oil was demonstrated as a typical example of application.     

Trace analysis of 1,10-phenanthroline based herbicide in water and soil samples

A sensitive analytical procedure for diquat herbicide viz. 5,6-dihydropyrazino[1,2,3,4-lmn]-1,10-phenanthrolinium dichlorides in drinking water and soil samples, using differential pulse adsorptive stripping voltammetry (DPAdSV) has been developed. This involved the adsorptive accumulation of a diquat herbicide onto a hanging mercury drop electrode [accumulation potential -0.8 V vs Ag/AgCl, accumulation time 60 s, pH 7.0, ionic strength 0.1 M] for DPAdSV measurement. The detection limit for diquat herbicide was as low as 0.034 micromol L(-1) level (S/N 2, RSD 2.9%) at an accumulation time of 60 s.     

Comparison of linear scan and differential pulse anodic stripping voltammetry at a thin mercury film glassy carbon electrode

The use of the differential pulse mode in anodic stripping voltammetry with an electrode consisting of a thin mercury film deposited in situ on a glassy carbon support leads to detection limits which are 3–5 times lower than if a simple linear scan is used at the same electrode. If the glassy carbon electrode has a high base current, the improvement in detection limit with differential pulse will be even greater. Differential pulse peak currents, however, are more susceptible to interference by surface-active substances, and undetected adsorption/desorption effects can cause serious errors. Precautions which are necessary to maintain a glassy carbon electrode in good condition are described.     

Electrochemistry at carbon fibers : Part 1. Characteristics of the Mercury Film Carbon Fiber Electrode in Differential Pulse Anodic Stripping Voltammetry

Carbon fibers are proposed as a support electrode for a mercury film electrode. The response of these electrodes is evaluated for use in differential pulse anodic stripping voltammetry. The mercury film is deposited in situ in aqueous solution and used to quantify cadmium in solutions of cadmium salts and organo cadmium compounds in the 1–10 μg l^-1 (ppb) concentration range. The good resolution and extremely low background current obtained allow a limit of detection at 0.04 μg Cd l^-1.     

Potentiometric stripping analysis

The analytical possibilities of potentiometric stripping analysis are outlined. The technique comprises reduction of metal ions at a stationary mercury drop or thin-film electrode. The amalgamated metals are then re-oxidized with mercury(II) ions, and the time—potential behaviour of the mercury electrode is recorded. The technique is compared with d.c. and differential pulse anodic stripping analysis.     

Digestion-free determination of heavy metals (Pb, Cd, Cu) in honey using anodic stripping differential pulse voltammetry and potentiometric stripping analysis

Experiments have been carried out to assess the potential of differential pulse voltammetry and potential stripping analysis for determining Pb, Cu and Cd directly in dissolved honey samples using a flow-through cell. With the hanging mercury drop electrode Pb alone can be determined only if the electrode is first modified in-situ with Triton X 100 to increase the separation between the Pb peak and a broad, interfering adsorption peak which overlaps the Cu peak. If the (more sensitive) thin film mercury electrode is used the interference encountered is less so also Cu and Cd can be determined. With potentiometric stripping analysis Cu and Pb can be determined using normal procedures. The determination of Cd, however, can only be carried out if the concentration of the oxidizing agent [Hg(II)] in solution is decreased. A good agreement has been obtained between the values found and those obtained after high pressure digestion of the samples.     

Determination of thiram in water and soils by cathodic stripping voltammetry based on adsorptive accumulation

Summary A very sensitive electrochemical stripping procedure for thiram is reported. Accumulation is achieved by adsorption of the compound on the hanging mercury drop electrode. Optimal experimental parameters include an accumulation potential of –0.2 V vs. Ag/AgCl, a 0.075 mol/l ammonia solution as supporting electrolyte and a differential pulse stripping mode. The detection limit is 0.3 ng ml^–1 after 120 s accumulation and 0.03 ng ml^–1 after 600 s accumulation. Results are reported for water and soil samples.

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Bestimmung von Thiram in Wasser und Böden mit Hilfe der Cathodic-Stripping Voltammetrie aufgrund adsorptiver Anreicherung

     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Adsorptive stripping voltammetry for the determination of nifedipine in human serum

Adsorptive stripping voltammetry is used for the determination of trace levels of nifedipine. The conditions for preconcentration on the mercury drop electrode have been studied and the final measurements are made by differential pulse voltammetry. The response is linear from 2 x 10(-9) to 1 x 10(-7)M and can be extended to 10(-6)M by a change in conditions. The stripping peak has been used for determination of the drug in formulations, with a relative standard deviation of 0.8%. The method is applicable to the determination of nifedipine in blood-serum with a detection limit of 4.1 ng/ml.     

Determination of azinphos-ethyl insecticide by adsorptive stripping voltammetry on the hanging mercury-drop electrode

The electrochemical characteristics of azinphos-ethyl (APE) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and adsorptive stripping voltammetry (ASV) at a hanging mercury drop electrode (HMDE) over a wide range of pH from 2.0 to 8.0. The cyclic voltammograms demonstrate the adsorption of this compound at the mercury electrode. A systematic study of the various operational parameters that affect the stripping response was carried out by differential pulse voltammetry (DPV). With a preconcentration potential of −0.6 V and a 60 s preconcentration time, the limit of detection was 5.42 × 10⁻⁹ M, and the relative standard deviation (n = 5) was 2.7 % at concentration level of 6.45 × 10⁻⁷ M APE. The degree of interference from diverse ions and some other pesticides on the differential pulse stripping signal for APE was evaluated. Finally, the method was applied to the determination of APM in spiked soil, tap water, and treated wastewater. The text was submitted by the author in English.