Application of a copper-based mercury film electrode in cathodic stripping voltammetry

The utility of a copper-based mercury film electrode (MFE) in cathodic stripping voltammetry (c.s.v.) is tested by comparing the cyclic and stripping voltammograms obtained with this electrode for thiocyanate, tryptophane, cysteine and benzotriazole against those obtained with the hanging copper-amalgam drop electrode (HCADE) and the HMDE. The cathodic stripping peaks obtained at the copper-based MFE and the HCADE are usually narrower and higher and are located at more negative potentials than the peaks obtained at the HMDE. Lower detection limits and better separations of adjacent peaks are thus achieved, and useful peaks can be separated from the mercury waves obtained with the conventional HMDE. The advantage of the copper-based MFE over the HCADE is its simplicity of preparation and maintenance. Thiocyanate, tryptophane, cysteine and benzotriazole can be determined at the copper-based MFE by c.s.v. with detection limits of 1 × 10^?8, 1 × 10^?8, 5 × 10^?8 mol dm^?3, respectively.     

Determination of traces of purine by cathodic stripping voltammetry at the hanging copper amalgam drop electrode

In the presence of purine, the copper(II)/copper(Hg) couple splits into copper(II)/copper(I) and copper(I)/copper(Hg) couples, which form two well-separated systems of peaks under voltammetric conditions. The copper(I)/purine complex adsorbs on the electrode surfacer and can be deposited on the electrode surface by electroreduction of copper(II) ions at the HMDE or by electro-oxidation of the hanging copper amalgam drop electrode (HCADE). The deposit can be stripped either cathodically or anodically over the pH range 2–9. The cathodic stripping variant at the HCADE, in solution with pH 2, offers the best results, with linear response for the range 5 × 10^?9–1.5 × 10^?7 mol dm^?3 purine after an accumulation time of 3 min. The detection limit found with the HMDE in the presence of copper(II) ions is higher.     

Cathodic and anodic stripping determination of traces of adenine and adenosine based on accumulation of copper(I) compounds at mercury or amalgam electrodes

In the presence of adenine and adenosine, the copper(II)/copper(Hg) couple splits to the copper(II)/copper(I) and copper(I)/copper(Hg) couples. Sparingly soluble complexes of copper(I) with adenine and adenosine can be accumulated on the electrode surface either by reduction of Cu(II) ions or by oxidation of the copper amalgam electrode. The copper(I)/adenine deposit can be stripped either cathodically or anodically with detection limits of 5×10^?9 and 2×10^?8 mol dm^?3, respectively. The copper(I)/ adenosine complex yields only the cathodic stripping peak with a detection limit of 9×10^?6 mol dm^?3. The stripping peaks obtained for the copper(I)/adenine and copper(I)/ adenosine complexes are better defined and appear over a wider range of pH than the peaks related to the corresponding mercury compounds. Adenosine cannot be determined in the presence of adenine bur adenine can be determined in the presence of moderate amounts of adenosine.     

The determination of traces of thiocyanate and copper(II) ions by cathodic stripping voltammetry

Cathodic stripping methods are described for the determination of traces of thiocyanate ions down to 2 × 10^-8 mol l^-1 and Cu(II) ions down to 1 × 10^-8 mol l^-1. The method involves electrolytic accumulation of copper(I) thiocyanate on the surface of a hanging mercury drop electrode followed by stripping of the deposit during the cathodic scan. For the determination of thiocyanate, a copper amalgam electrode can be used. Examples of application of the method for the determination of traces of thiocyanate in common salts, in saliva and urine as well as for the determination of copper(II) ions in tap water are described.     

Electrochemical Behavior of 6-Mercapto-Purine at Hanging Copper Amalgam Dropping Electrode and Its Trace Determination by Differential Pulse Adsorption Cathodic Stripping Voltammetry

Abstract

The electrochemical behavior of 6-MP was studied by cyclic voltammetry at a hanging copper amalgam dropping electrode (HCADE). It was found that 6-MP could form a complex with the Cu(II) stripped from the HCADE, showing a new peak at ?0.19V in the medium of 0.1mol/L LiClO₄-0.5mol/L HClO₄ solution. The mechanism of the reaction was proposed. This new peak was sensitive and could be used for the determination of trace 6-MP by differential pulse adsorption cathodic stripping voltammetry (DPAdCSV). The linear range was from 3.6×10^?10 to 5.3×10^?6 mol/L, and the detection limit was about 1.2×10^?10 mol/L (S/N=3). The method was also successfully applied to the determination of 6-MP in pharmaceutical tablets.     

Electrochemical reduction behaviour of the synthetic pyrethroid insecticide cyfluthrin and its determination in formulations and environmental samples

The polarographic behaviour of cyfluthrin (CY), an α-cynoester pyrethroid, was studied using a dropping mercury electrode and hanging mercury drop electrode in methanolic Britton–Robinson (B–R) buffer of pH 2.0–12.0 with different ionic media. The nature of the electrode process was examined, the number of electrons was evaluated, and the reduction mechanism was proposed. Quantitative determination was achieved in the concentration range of 6.0?×?10^?8 to 1.15?×?10^?5?mol?dm^?3 using a differential pulse polarographic method with a lower detection limit of 2.4?×?10^?8?mol?dm^?3. The proposed method was successfully applied in the determination of CY in formulations, grains, soils, and spiked water samples.     

Direct determination of traces of silver in mercury by voltammetry at the hanging mercury drop electrode in acetonitrile medium

A direct method for the determination of silver in mercury is described. The sample of mercury is introduced into the container of the hanging mercury drop electrode and the anodic voltammograms are recorded in a 0.1 M lithium perchlorate solution in acetonitrile. The anodic peak of silver obtained under these conditions is well separated from the mercury dissolution current. The peak height is proportional to silver concentration over the wide range 2 × 10^?6 mol dm^?3 (1.6 × 10^?6%) to at least 2.0 × 10^?2 mol dm^?3. No prior separation is needed; the procedure requires less than 20 min. The diffusion coefficient of silver in mercury was determined at several temperatures. It was found that silver in mercury does not form intermetallic compounds with copper, lead, thallium, cadmium, tin and bismuth.     

Cathodic stripping voltammetry of 2-mercaptoethanol

The behaviour of 2-mercaptoethanol at a hanging mercury drop electrode by cathodic stripping voltammetry (c.s.v.) is studied. The stripping curves are recorded by three scanning modes: rapid-scan direct-current, differential-pulse and fundamental harmonic alternating-current polarography. Under the recommended conditions, pre-electrolysis is done at a potential of 0.0 V vs. Ag/AgCl for 3 min in a medium of pH 6.7 or 8 (Britton-Robinson buffer). Then after 1 min, stripping is done at a scan rate of 6.6 mV s^?1 preferably in the differential-pulse mode. The stripping peak at about ?0.4 V is used to determine 2-mercaptoethanol within the concentration range 3 × 10^?8/2-8 × 10^?7 mol l^?1. Calibration functions are reported; the standard additions method is preferred near the limit of detection. The interferences of several organic compounds are described.     

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.     

A Validated Voltammetric Procedure for Quantification of the Antifungal Drug Griseofulvin in Bulk Form,Tablets, and Biological Fluids at a Mercury Electrode

Abstract

Griseofulvin is an antifungal antibiotic used to treat various pathogenic mycotic diseases. The voltammetric behavior of griseofulvin at a hanging mercury drop electrode in Britton‐Robinson buffers of pH 2–11.5 was studied and discussed. A fully validated sensitive square‐wave adsorptive cathodic stripping voltammetric procedure was described for direct determination of bulk griseofulvin substance. The procedure was based on the reduction of the >C?O double bond of griseofulvin molecule following its preconcentration onto a hanging mercury drop electrode in a Britton‐Robinson buffer of pH 10. Limits of detection (LOD) and quantitation (LOQ) of 5.8×10^?10 M and 1.93×10^?9 M bulk griseofulvin were achieved, respectively. The proposed stripping voltammetric procedure was successfully applied to assay griseofulvin in tablets and in spiked human serum and urine samples. LOD of 8.65×10^?10 M and 6.6×10^?9 M and LOQ of 2.88×10^?9 M and 2.2×10^?8 M griseofulvin in spiked human serum and urine samples, respectively, were achieved.     

Chemical Speciation of Antimony(III and V) in Water by Adsorptive Cathodic Stripping Voltammetry Using the 4‐(2‐Thiazolylazo) – Resorcinol

A simple adsorptive cathodic stripping voltammetry method has been developed for antimony (III and V) speciation using 4‐(2‐thiazolylazo) – resorcinol (TAR). The methodology involves controlled preconcentration at pH 5, during which antimony(III) – TAR complex is adsorbed onto a hanging mercury drop electrode followed by measuring the cathodic peak current (I_p,c) at ?0.39 V versus Ag/AgCl electrode. The plot of I_p,c versus antimony(III) concentration was linear in the range 1.35×10^?9–9.53×10^?8 mol L^?1.The LOD and LOQ for Sb(III) were found 4.06×10^?10 and 1.35×10^?9 mol L^?1, respectively. Antimony(V) species after reduction to antimony(III) with Na₂SO₃ were also determined. Analysis of antimony in environment water samples was applied satisfactorily.     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily     

Cathodic Stripping Voltammetry Determination of Ceftiofur Antibiotic in Formulations and Bovine Serum

Abstract

A sensitive and reliable stripping voltammetry method was developed to determine the presence of Ceftiofur antibiotic drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then the initiation of a negative sweep that yielded well‐defined cathodic peaks at ?0.65 V (1 C) and ?1.00 V (2 C) vs. Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, convection rate, and working electrode area. The monitored adsorptive current of peak 1 C was directly proportional to the concentration of Ceftiofur; it shows a linear response in the range from 0.50×10^?8 to 8.00×10^?8 mol L^?1 (correlation coefficient=0.998); and the limit of detection is 6.00×10^?10 mol L^?1 at an accumulation time of 300 s. The applicability of this approach was illustrated by the determination of Ceftiofur in pharmaceutical preparations and bovine serum.     

Cathodic stripping voltammetry and adsorptive stripping voltammetry of selenium(IV)

Cathodic stripping voltammetry of selenium(IV) in 0.1 M hydrochloric acid media yielded a nonlinear calibration graph for the concentration range 10^?9?10^?8 M. In this concentration range, adsorptive stripping voltammetry based on adsorption of the selenium/3,3′-diaminobenzidine complex on the surface of the hanging mercury drop electrode at the deposition potential of +0.05 V (vs. SCE) is more convenient. A linear calibration graph is obtained for selenium concentrations of 3×10^?9?3×10?8 M, with an accumulation time of 300 s.     

Electrochemical Study of Moroxydine and its Voltammetric Determination with a Silver Amalgam Film Electrode

Moroxydine (Mor.) is an antiviral agent of biguanide structure. The paper presents a new silver amalgam film electrode (Hg(Ag)FE) for determination of Mor. in phosphate buffer, pH 6.2 (LOD=4×10^?9 mol L^?1, LOQ= 1×10^?8 mol L^?1) and in spiked urine using square wave adsorptive stripping voltammetry. It was found that the compound can act as an electrocatalyst not only at hanging mercury drop electrode but also at the Hg(Ag)FE. The electrode mechanism is connected with the hydrogen evolution reaction catalyzed by moroxydine. Adsorption of moroxydine at the mercury electrode was studied and special arrangements of molecules enabling electron transfer of the protonated form of moroxydine is suggested.     

Electrochemical Studies and Square‐Wave Adsorptive Stripping Voltammetry of Spironolactone Drug

Abstract

A sensitive and reliable stripping voltammetric method was developed to determine Spironolactone drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then a negative sweep was initiated, which yield a well defined cathodic peak at ?1000 mV versus Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, frequency, pulse amplitude, convection rate and working electrode area. The monitored adsorptive current was directly proportional to the concentration of Spironolactone and it shows a linear response in the range from 1×10^?8 to 2.5×10^?7 mol l^?1 (correlation coefficient=0.999) and the detection limit (S/N=3) is 1.72×10^?10 mol l^?1 at an accumulation time of 90 sec. The developed AdSV procedure shows a good reproducibility, the relative standard deviation RSD% (n=8) at a concentration level of 1.5×10^?7 mol l^?1 was 1.4%, whereas the method accuracy was indicated via the mean recovery of 97.5%±2.04. Possible interferences by several substances usually present in the pharmaceutical formulations have been also evaluated. The applicability of this approach was illustrated by the determination of Spironolactone in pharmaceutical preparation and biological fluids such as serum and urine.     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily Received: 10 July 1997 / Revised: 1 April 1998 / Accepted: 6 April 1998     

Response surface methodology for optimisation of 4,6-Dinitro-o-cresol quantification using hanging mercury drop electrode

A method for the pesticide DNOC (4,6-Dinitro-o-cresol) quantification using hanging mercury drop electrode (HMDE) and stripping square wave voltammetry (SSWV) optimisation is proposed. As a continuous cathodic current decrease was observed during the experiments, a waiting time, together with solution pH and SWV instrumental variables were optimised by factorial designs. From the two reduction current peaks values, only one was considered as dependent variable in the optimisation process. While the cathodic current peak and standard deviation were used in the waiting time and solution pH optimisation process, the instrumental parameters for SWV were optimised by using only current peak values. With the optimal parameters, a calibration curve from (0.01–0.55) × 10^?6 mol L^?1 with LOD of 2 × 10^?8 mol L^?1 was obtained. The proposed method was checked for DNOC quantification in different water samples obtained from Cordoba area and very good results, with recovery values around 102% were observed.     

Adsorptive Cathodic Stripping Voltammetry Determination of Ultra Trace of Lead in Different Real Samples

Abstract

In the present work, an adsorptive cathodic stripping voltammetric method using a hanging mercury drop electrode (HMDE) was described in order to determine the ultra trace of lead ions with carbidopa in different real samples. The method is based on accumulation of lead metal ion on mercury electrode using carbidopa as a suitable complexing agent. The potential was scanned to the negative direction and the differential pulse stripping voltammograms were recorded. The instrumental and chemical parameters were optimized. The optimized conditions were obtained in pH of 8.4, carbidopa amount of 1.0×10^?6 M, accumulation potential of 0. 0 V, accumulation time of 100 s, scan rate of 100 mV/s and pulse height of 50 mV. The relationship between the peak current versus concentration was linear over the range of 2.4×10^?10–4.8×10^?7 M. The limits of detection were 5.8×10^?11 M and the relative standard deviation at 4.8×10^?10, 2.1×10^?8, and 2.4×10^?7 M of lead ion were obtained 3.2, 2.9, and 2.7%, respectively (n=7).     

Investigations on Bioanalytical Chemistry Part I. On Differential Pulse Voltammetry of Bilirubin

Abstract

The electrochemical behaviour of the bilirubin in many kinds of supporting electrolytes on a glassy carbon electrode (GCE) and a hanging mercury drop electrode (HMDE) was investigated by means of anodic or cathodic differential pulse voltammetry. The influences of different methods of pre-treatment of the glassy carbon electrode was also discussed. In Na₂B₄.O₇-KH₂PO₄ buffer solution, the linear range was 2×10^?9-1×10^?9 mol/l and the detection limit was 3.3×10^?9 mol/l by anodic differential pulse voltammetry at GCE. A linear relationship holds between the peak current and the concentration of bilirubin in a concentration range of 1×10^?9-4×10^?7 mol/l with good precision and accuracy, and the limit of detection was 2×10^?10 mol/l, when cathodic differential pulse adsorption voltammetry at HMDE was used.