Highly sensitive and selective measurements of cobalt by catalytic adsorptive cathodic stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of the cobalt-MTB (methyl thymol blue) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The optimum conditions for the analysis of cobalt include pH 9.0 (ammonia buffer), 2.0 μM methyl thymol blue, 0.8 M sodium nitrite and an accumulation potential of −0.5 V (versus Ag/AgCl). The peak current is proportional to the concentration of cobalt over the entire concentration range tested (0.02–500 ng ml⁻¹) with a detection limit of 0.005 ng ml⁻¹ for an accumulation time of 60 s. The method was applied to determination of cobalt in a mineral water sample and some analytical grade salts with satisfactory results.     

High sensitive determination of trace amount of cobalt by catalytic adsorptive stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of cobalt-CCA (calcon carboxylic acid) complex onto a hanging mercury drop electrode followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The effect of various parameters such as pH, concentration of CCA, concentration of nitrite, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum condition for the analysis of cobalt, include pH 5.2 (Acetate buffer), 2.1 μM clacon carboxylic acid, 0.032 M sodium nitrite and an accumulation potential of 0.05 V (versus Ag/AgCl). Under these optimum conditions and for an accumulation time of 60 s, the measured peak current at −0.480 V is proportional to the concentration of cobalt over the entire concentration range tested 0.003–2.0 ng ml⁻¹ with a detection limit of 1 pg ml⁻¹ for an accumulation time of 60 s and 2.0–10.0 ng ml⁻¹ for an accumulation time of 40 s. The relative standard deviations for ten replicate measurement of 0.5 ng ml⁻¹ of cobalt were 3.1%. The main advantage of this new system is the microtrace Co(II) determination by ASV. The method was applied to determination of cobalt in a water sample and some analytical grade salts with satisfactory results. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 2, pp. 221–228. The article is published in the original.     

Cyclopentanone thiosemicarbazone, a new complexing agent for copper determination in biological samples by adsorptive stripping voltammetry.

A selective and sensitive stripping voltammetric method for the determination of trace amounts of copper(II) with cyclopentanone thiosemicarbazone (CPTSC) is presented. The method is based on the adsorptive accumulation of the resulting copper-CPTSC complex on a hanging mercury drop electrode, followed by the stripping voltammetric measurements at the reduction current of the adsorbed complex at -0.37 V vs. Ag/AgCl. The optimal conditions for the stripping analysis of copper include pH 9.3, deposition time of 120 s, and a deposition potential of -0.1 V (vs. Ag/AgCl). The peak current is linearly proportional to the copper concentration over a range 3.14 x 10(-9) M to 1.57 x 10(-6) M with a limit of detection of 1.57 x 10(-9) M. The technique has been applied to the determination of copper in biological samples, like urine and whole blood.     

Selective determination of trace copper(II) by cathodic adsorptive stripping voltammetry with a naphthol-derivative Schiff's base

A selective and sensitive stripping voltammetric method for the determination of trace amounts of copper(II) with a recently synthesized naphthol-derivative Schiff's base (2,2'-[1,2-ethanediylbis(nitriloethylidyne)]bis(1-naphthalene)) is presented. The method is based on adsorptive accumulation of the resulting copper-Schiff's base complex on a hanging mercury drop electrode, followed by the stripping voltammetric measurement at the reduction current of adsorbed complex at -0.15 V (vs. Ag/AgCl). The optimal conditions for the stripping analysis of copper include pH 5.5 to 6.5, 8 microM Schiff's base and an accumulation potential of -0.05 V (vs. Ag/AgCI). The peak current is linearly proportional to the copper concentration over a range 2.3-50.8 ng ml(-1) with a limit of detection of 1.9 ng ml(-1). The accumulation time and RSD are 90 s and (3.2-3.5)%, respectively. The method was applied to the determination of copper in some analytical grade salts, tap water, human serum and sheep's liver.     

The Use of Ultrasound for the Analytical Determination of Nitrite on Diamond Electrodes by Square Wave Voltammetry

Abstract

This work describes an analytical methodology for the determination of nitrite ions in aqueous solutions using boron‐doped diamond electrodes and square wave voltammetry associated with ultrasound radiation. The nitrite ions were oxidized to nitrate ions in Britton‐Robinson buffer solutions 0.1 M, pH 2.0 at 1.0 V versus Ag/AgCl. The voltammetric response of nitrite in the presence of ultrasound showed a peak current five times higher than the obtained in silent conditions. Thus, the detection limit obtained in the presence of radiation was 17 nM (0.782 µg l^?1), a small value if compared with that obtained in the absence of ultrasound: 140 nM (6.44 µg l^?1).     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite

A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated. Received: 17 August 1998 / Revised: 16 November 1998 / Accepted: 20 November 1998     

Highly sensitive adsorptive stripping voltammetric method for the ultra-trace determination of chromium(VI).

A rapid differential pulse adsorptive stripping voltammetric method has been developed for the ultra-trace determination of chromium using 2,2'-bipyridine. The base electrolyte used is 0.1 M NH4Cl (pH 6.0). The peak current was found to increase substantially with the addition of nitrite ions. A well-defined peak was observed at -1.3 V. Parameters, like concentration of the ligand, concentration of nitrite ion, accumulation potential, accumulation time, rest period, drop size, scan rate, pulse amplitude etc. have been optimized. Under the optimum conditions, the 3 sigma detection limit was found to be 0.02 ppb (3.8 x 10(-10) M). The method is highly selective and sensitive, and has been applied to the determination of Cr(VI) in spiked water, effluents and ore samples.     

Determination of trace thorium using catalytic-adsorptive stripping voltammetry of the thorium-cupferron complex

A sensitive stripping voltammetric procedure for trace measurement of thorium, based on the catalytic-adsorptive peak of the thorium-cupferron complex, is reported. Optimal experimental conditions include the use of 1mM BES buffer solution (pH 5.5), containing 20muM cupferron, an accumulation potential of -0.80 V (vs. Ag/AgCl), and a differential pulse potential scan. The resulting stripping procedure offers improved sensitivity over a previous stripping scheme for thorium. The limit of detection after 5 min preconcentration is 50 ng/l. (2 x 10(-10)M), the response is linear up to 8 x 10(-8)M, and the relative standard deviation at the 2.1 x 10(-8)M level is 4.4%. Possible interferences are evaluated.     

Redox characteristics of Schiff base manganese and cobalt complexes related to water-oxidizing complex of photosynthesis

In an effort to obtain synthetic analogues of water-oxidizing complex (WOC) of photosystem II (PS II) of plant photosynthesis, a Schiff base manganese and a cobalt complex, employing Niten, a SALEN type ligand, have been prepared. Cyclic and square wave voltammetric measurements have been performed to assess their redox characteristics. Both complexes undergo several reduction processes in cathodic negative potential region at more or less similar potentials. In view of these reductions being independent of the nature of the metal, they are thought to be ligand-localized. Although similar in negative region, a marked difference in the behavior of the complexes is observed in anodic region. While the cobalt complex is electrochemically inactive in the positive potentials up to +1.0 V vs. Ag/AgCl, the manganese complex displays two oxidation waves at +0.25 and +0.5 V vs. Ag/AgCl. The presence of oxidation wave in manganese complex at +0.5 V vs. Ag/AgCl or +0.7 V vs. NHE suggests that this complex can catalyze the oxidation of water and can, thus, simulate the WOC of PS II.     

Voltammetric Detection of Catechol and Dopamine Based on a Supramolecular Composite Prepared from Multifarene[3,3] and Reduced Graphene Oxide

A selective and sensitive modified‐electrode for catechol and dopamine was presented with supramolecular recognition accomplished by making use of the macrocyclic host multifarene[3,3] that was used as a composite with reduced graphene oxide. The morphologies and electrochemical nature of the composite were characterized by atomic force microscopy, transmission electron microscopy, cyclic voltammetry and differential pulse anodic voltammetry. The modified electrode, best operated at a potential around 0.16 V vs. Ag/AgCl, displayed a differential pulse voltammetric response in the linear concentration range of 10–100 nM within a detection limit of 0.51 nM (at S/N=3). It was further applied to detect dopamine (at a working potential of 0.18 V vs. Ag/AgCl) in the linear concentration range of 10–100 nM with a detection limit of 0.62 nM. The modified electrode also exhibited satisfactory results to the determination of dopamine injections. The constructed modified electrode for dopamine detection was investigated in the presence of the interfering substances including glucose, urea and ascorbic acid, indicating a good selectivity.     

Adsorptive stripping voltammetric determination of midazolam as a method for quality control

Controlled interfacial accumulation of the benzodiazepine midazolam at a hanging mercury drop electrode provides the basis for a highly sensitive and accurate adsorptive stripping voltammetric procedure. The response was linear in the range 1.9 × 10^?6? × 10^?9 M when using a 120-s preconcentration at ?0.45 V vs. Ag/AgCl in Britton-Robinson buffer of pH 5.00. In this range the relative standard deviation was between 1.21 and 1.62%. The applicability of the method to pharmaceutical preparations is discussed.     

Quantification of terbutaline in pharmaceutical formulation and human serum by adsorptive stripping voltammetry at a glassy carbon electrode

The electrochemical oxidative behavior of terbutaline at the glassy carbon electrode was studied in a series of the Britton-Robinson buffer of pH 2--11. Cyclic and square-wave voltammograms of terbutaline at the pH values 相似文献   

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO(2))L(bpy)(2)](+) complex

The synthesis of [Ru(NO(2))L(bpy)(2)](+) (bpy = 2,2'-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)(2)](PF(6))(3) to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO(2))L(bpy)(2)](+) in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS(+) and spectroelectrochemical experiment where cis-[Ru(bpy)(2)L(H(2)O)](2+) was obtained as a product of the reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 mumol L(-1) phenylephrine responded with relaxation in the presence of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The potential of rat aorta cells to metabolize cis-[Ru(II)(NO(2))L(bpy)(2)](+) was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+) inside the cell. The maximum vasorelaxation was achieved with 1 x 10(-5) mol L(-1) of cis-[Ru(II)(NO(2))L(bpy)(2)](+) complex.     

Adsorptive stripping voltammetric assay of phenazopyridine hydrochloride in biological fluids and pharmaceutical preparations

A sensitive method for the measurement of phenazopyridine hydrochloride (PAP) by differential pulse polarography (DPP) based on adsorptive stripping technique, using a hanging mercury drop electrode (HMDE) is described. The voltammetric peak is obtained at -0.760 V, which corresponds to the reduction of the azo group in Britton-Robinson buffer. The redox behaviour is reversible. Optimum conditions were found to be: accumulation potential -50 mV (vs. Ag/AgCl), accumulation time 60 s, scan rate 5 mV s(-1), pulse amplitude -100 mV and supporting electrolyte Britton-Robinson buffer (0.04 M, pH=11). The relative standard deviation (at 20 ng ml(-1) level) was +/-0.6% for six measurements. The calculated detection limit was 0.0299 ng ml(-1) with a 60-s accumulation time. The applicability of such a method was evaluated through the assay of PAP in human plasma and urine samples after a simple extraction procedure and in pharmaceutical preparation. The mean recovery was 97+/-2 (100 ng ml(-1) plasma).     

Electrochemical study of zolpidem at glassy carbon electrode and its determination in a tablet dosage form by differential pulse voltammetry

The oxidative behaviour of, a hypnotic drug, zolpidem was studied at glassy carbon electrode in Britton-Robinson buffer over the pH range 2.0-11.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single irreversible, diffusion-controlled step. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 8.0 at +0.889 V (vs. Ag/AgCl) on glassy carbon electrode. This process could be used to determine zolpidem concentrations in the range 5.0 x 10(-7) M to 1.0 x 10(-5) M with a detection limit of 2.0 x 10(-7) M. The method was applied, without any interference from the excipients, to the determination of the drug in a tablet dosage form.     

Adsorptive stripping measurements of germanium(IV) in the presence of pyrogallol

The adsorptive stripping voltammetric determination of germanium(IV) based on the adsorptive accumulation of the germanium(IV)-pyrogallol complex on a hanging mercury drop electrode is reported. The reduction current of the adsorbed germanium complex is measured by differential-pulse cathodic stripping voltammetry. The peak potential is at -0.42 V vs. Ag AgCl (saturated KCL). The effects of various parameters (ligand concentration, supporting electrolytic composition and concentration, accumulation potential and collection time) on the response are discussed. With controlled accumulation for 3 min, the detection limit is 1.2 x 10(-9) M germanium. The relative standard deviation (at 1.2 x 10(-8) M germanium) is 3.6%. Possible interferences are evaluated. The applicability of the method to the determination of germanium(IV) in ore samples was also successfully carried out.     

Electrocatalytic detection of polysaccharides at picomolar concentrations

Electroinactive polysaccharides (PS) modified by osmium(VI) complexes with nitrogenous ligands produce redox couples at carbon and mercury electrodes. We show that PS adducts with Os(VI) 2,2'-bipyridine produce at ~-1.2 V (against Ag/AgCl/3 M KCl electrode) an additional peak at mercury and solid amalgam electrodes. This peak is due to the catalytic hydrogen evolution, allowing detection of PS (such as dextran and mannan) at picomolar concentrations.     

Simultaneous square-wave voltammetric determination of acetazolamide and theophylline in pharmaceutical formulations

Simple, rapid, sensitive and low cost voltammetric method for simultaneous determination of acetazolamide and theophylline in pharmaceutical formulations, was developed using a static mercury drop electrode (SMDE). Well-defined voltammetric peaks were obtained at–0.87 and–1.33 V for acetazolamide and–0.21 V (vs. Ag/AgCl) for theophylline in Britton–Robinson (B–R) buffer (pH 2.4). The reduction peak currents are found to be linearly dependent on the concentration for the both drugs. Calibration graphs were obtained over the concentration range 1.98 × 10^–6 to 5.94 × 10^–5 M and 2.0 × 10^–5 to 5.6 × 10^–4 M for acetazolamide and theophylline, respectively. The limits of detection (LOD) and quantitation (LOQ) of the procedure were also presented. Factors such as, pH of supporting electrolyte, equilibrium time, frequency, scan rate and pulse height were optimized. The validated voltammetric method was successfully applied for simultaneous determinations of the two drugs. The procedure does not require any sample pretreatment or timeconsuming separation steps.     

Electrochemical study of the antineoplastic agent etoposide at carbon paste electrode and its determination in spiked human serum by differential pulse voltammetry

The electrochemical oxidation of the antineoplastic agent etoposide was studied at carbon paste electrode in Britton-Robinson buffer solutions over the pH range 2.0-10.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single reversible, diffusion-controlled step within the pH range 2.0-4.0, a second oxidation process was produced above pH 4.0. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 3.0 at 0.500 V (vs. Ag/AgCl) on carbon paste electrode. This process could be used to determine etoposide concentrations in the range 2.5 x 10(-7) to 2.5 x 10(-5) M with a detection limit of 1.0 x 10(-7) M. The method was successfully applied to the determination of the drug in spiked human serum.