Determination of Nanomolar Concentrations of Pb(II) Using Carbon Paste Electrode Modified with Zirconium Phosphated Amorphous Silica

A sensitive and selective method for the determination of Pb(II) with a zirconium phosphated silica gel (SiZrPH) modified carbon paste electrode has been developed. The measurements were carried out in three steps including an open circuit accumulation following by electrolysis of accumulated Pb(II) at the modified carbon paste electrode and differential pulse voltammetric determination. The analytical performance was evaluated with respect to the carbon paste composition, pH of solution at the accumulation step, pH and concentration of supporting electrolyte, electrolysis potential, accumulation time and electrolysis time. Two linear calibration graphs were obtained in the concentration ranges 2.5×10^?9 mol L^?1–5.0×10^?8 mol L^?1 and 5.0×10^?8 mol L^?1–5.0×10^?6 mol L^?1 with an accumulation time of 120 s. The detection limit was found to be 3.5×10^?10 mol L^?1. The effects of potential interfering ions were studied, and it was found that the proposed procedure is free from interferences of common interfering ions such as tin, thallium and etc. The developed method was applied to Pb(II) determination in a wastewater sample.     

Determination of lead(II) in aqueous solution using carbon nanotubes paste electrodes modified with Amberlite IR-120

A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of multiwalled carbon nanotubes and Amberlite IR-120. The anodic stripping voltammograms depend, to a large extent, on the composition of the modified electrode and the preconcentration conditions. Under optimum conditions, the anodic peak current at around ?0.57 V is linearly related to the concentration of Pb(II) in the range from 9.6?×?10^?8 to 1.7?×?10^?6 mol L^?1 (R?=?0.998). The detection limit is 2.1?×?10^?8 mol L^?1, and the relative standard deviation (RSD) at 0.24?×?10^?6 mol L^?1 is 1.7% (n?=?6). The modified electrode was applied to the determination of Pb(II) using the standard addition method; the results showed average relative recoveries of 95% for the samples analysed.

Adsorptive Cathodic Stripping Voltammetric Method for Determination of Gallium Using an In Situ Plated Lead Film Electrode

The in situ plated lead film electrode was proposed for the first time for adsorptive stripping voltammetric determination of gallium in water samples. The method was based on simultaneous lead film formation and Ga(III)‐cupferron complex preconcentration at ?0.7 V and its cathodic stripping during the potential scan. The composition of the supporting electrolyte, cupferron concentration, conditions of lead film formation, potential and time of accumulation were studied in detail. Under optimum conditions the limit of detection was 3.8×10^?9 mol L^?1. The proposed procedure was validated in the course of Ga(III) determination in waste water certified reference materials.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Dimethylglyoxime and Nitrite at In Situ Plated Lead–Copper Film Electrode

A lead‐copper film electrode was proposed for Co(II) determination by catalytic adsorptive stripping voltammetry. The electrode was plated in situ and hence the exchange of a solution after plating step was not required. At optimized conditions the calibration graph for Co(II) was linear from 5×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 15 s. The relative standard deviation for Co(II) determination at concentration 5×10^?9 mol L^?1 was 4.1%. The detection limits for Co(II) were 1.2×10^?10 and 1.0×10^?11 mol L^?1 for an accumulation time of 15 and 180 s, respectively. The method was applied to Co(II) determination in certified reference material and other water samples.     

Sensitive Anodic Stripping Voltammetric Copper Ions Determination Performed in Double Deposition and Double Stripping Steps System for Real Water Samples Analysis

The article reports on utilization of double deposition and stripping steps for increasing sensitivity of Cu(II) determination by anodic stripping voltammetry (ASV) at two lead film working electrodes. A significant preconcentration of copper was achieved thanks to utilization of a simple design of four electrodes system that gives possibility to perform one measurement cycle consisting of two deposition and two stripping steps. Due to the fact that deposition step is doubled, the concentration of Pb(II) needed to lead film electrodes formation was significantly reduced as compared to traditional procedures using three electrodes system. The analytical procedure of Cu(II) determination was optimized. The experimental factors: supporting electrolyte's pH and its concentration, lead ions concentration, potential and time of deposition at both working electrodes were studied. The Cu(II) peak current was linearly dependent on its concentration from 5×10^?10 to 2×10^?8 mol L^?1 (deposition time of 270 and 160 s at the first and the second working electrode, respectively). The obtained detection limit for copper ions determination was 2.1×10^?10 mol L^?1. The described procedure was validated by analysis of two water certified reference materials. The described procedure was also utilized for real water sample analysis.     

Fast Simultaneous Adsorptive Stripping Voltammetric Determination of Ni(II) and Co(II) at Lead Film Electrode Plated on Gold Substrate

A fast adsorptive stripping voltammetric procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The time of determination of these ions was shortened due to the application of gold as a substrate for lead film. At gold substrate lead film formation and accumulation of Ni(II) and Co(II) complexes with nioxime proceeds simultaneously. To obtain a stable signals for both ions a simple procedure of activation of the electrode was proposed. Calibration graphs for an accumulation time of 20 s were linear from 5×10^?9 to 1×10^?7 mol L^?1 and from 5×10^?10 to 1×10^?8 mol L^?1 for Ni(II) and Co(II), respectively. The procedure with the application of a lead film electrode on a gold substrate was validated in the course of Ni(II) and Co(II) determination in certified reference materials.     

Novel sensor based on carbon paste/Nafion? modified with gold nanoparticles for the determination of glutathione

Several problems for the direct electrochemical oxidation of reduced glutathione (GSH) challenge the usage of electroanalytical techniques for its determination. In this work, the electrochemical oxidation of GSH catalyzed by gold nanoparticles electrodeposited on Nafion modified carbon paste electrode in 0.04?mol?L^?1 universal buffer solution (pH?7.4) is proved successful. The effect of various experimental parameters including pH, scan rate and stability on the voltammetric response of GSH was investigated. At the optimum conditions, the concentration of GSH was determined using differential pulse voltammetry (DPV) in two concentration ranges: 0.1?×?10^?7 to 1.6?×?10^?5?mol?L^?1 and 2.0?×?10^?5 to 2.0?×?10^?4?mol?L^?1 with correlation coefficients 0.9988, 0.9949 and the limit of detections (LOD) are 3.9?×?10^?9?mol?L^?1 and 8.2?×?10^?8?mol?L^?1, respectively, which confirmed the sensitivity of the electrode. The high sensitivity, wide linear range, good stability and reproducibility, and the minimal surface fouling make this modified electrode useful for the determination of spiked GSH in urine samples and in tablet with excellent recovery results obtained.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

Renewable Ceramic (TiN) Ring Electrode in Stripping Voltammetry. Determination of Pb(II) Without Removal of Oxygen

Characteristic features of the process of Pb(II) reduction and oxidation at a renewable ceramic ring electrode (RCRE) were studied by stripping voltammetry. The main constituents of the RCRE are: a specially constructed TiN ring electrode, a silver sheet used as silver counter/quasi‐reference electrode and a silicon O‐ring are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RCRE body. The optimal measurement conditions, composition of supporting electrolyte and procedures of the electrode activation were selected. The measurements were carried out from nondeaerated solutions. As shown on selected examples, RCRE exhibits good performance in underpotential deposition stripping voltammetry (UPD‐SV) applied for the determination of lead(II) in synthetic solutions with and without surfactants and in certified reference materials. The peak current is proportional to the concentration of lead(II) over the range 2×10^?9–1×10^?7 mol L^?1, with a 3σ detection limit of 1×10^?9 mol L^?1 with an accumulation time of 30 s. The obtained results showed good reproducibility, (RSD=2–5%; n=5) and reliability.     

Lead(II) Potentiometric Sensor Based on 1,4,8,11‐Tetrathiacyclotetradecane Neutral Carrier and Lipophilic Additives

A potentiometric sensor for lead(II) ions based on the use of 1,4,8,11‐tetrathiacyclotetradecane (TTCTD) as a neutral ionophore and potassium tetrakis‐(p‐chlorophenyl)borate as a lipophilic additive in plasticized PVC membranes is developed. The sensor exhibits linear potentiometric response towards lead(II) ions over the concentration range of 1.0×10^?5–1.0×10^?2 mol L^?1 with a Nernstian slope of 29.9 mV decade^?1 and a lower limit of detection of 2.2×10^?6 mol L^?1 Pb(II) ions over the pH range of 3–6.5. Sensor membrane without a lipophilic additive displays poor response. The sensor shows high selectivity for Pb(II) over a wide variety of alkali, alkaline earth and transition metal ions. The sensor shows long life span, high reproducibility, fast response and long term stability. Validation of the method by measuring the lower limit of detection, lower limit of linear range, accuracy, precision and sensitivity reveals good performance characteristics of the proposed sensor. The developed sensor is successfully applied to direct determination of lead(II) in real samples. The sensor is also used as an indicator electrode for the potentiometric titration of Pb(II) with EDTA and potassium chromate. The results obtained agree fairly well with data obtained by AAS.     

A new voltammetric sensor for the determination of sulfite in water and wastewater using modified-multiwall carbon nanotubes paste electrode

The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10^?7–2.8?×?10^?4?mol?L^?1 with a detection limit of 9.0?×?10^?8?mol?L^?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L^?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples.     

Determination of lead (II) ion by highly selective and sensitive lead (II) membrane electrode based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl) methyliden)hydrazono)metyl)phenol

A PVC (poly vinyl chloride) membrane electrode for lead ion based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl)methyliden)hydrazono)metyl)phenol (HMHMP) as a membrane carrier was prepared. This electrode exhibited linear response with Nernstian slope of 29.2?±?0.2?mV per decade within the concentration range of 2.0?×?10^?7–1.0?×?10^?1?M lead ion. The limit of detection, as determined from the intersection of the extrapolated linear segments of the calibration plot, was 8.0?×?10^?8 M. The electrode exhibited high selectivity for Pb (II). The response time of the electrode was about 5–10?s for different concentrations. The electrode is suitable for use in aqueous solutions in a pH range of 5.0–7.5. It was used as an indicator electrode in a titration of Pb (II) with chromate at constant pH. This electrode was used for the determination of lead in ore samples, and the results were in agreement with those obtained with an atomic absorption spectroscopy (AAS) method. Also lead selective electrode was used for monitoring of lead in spiked samples of the Zayanderud River and waste water by the potentiometry technique.     

Determination of cadmium(II) using glassy carbon electrodes modified with cupferron, ß-naphthol, and multiwalled carbon nanotubes

We report on a simple and reliable method for the determination of trace cadmium ion using a glassy carbon electrode (GCE) modified with cupferron, ß-naphthol and MWCNTs. The operational mechanism consists of several steps: first, the ligand cupferron on the modified electrode reacts with Cd²⁺ ion to form a chelate compound. Next, this chelate is adsorbed by the carrier ß-naphthol following the principle of organic co-precipitation. Finally, the coprecipitated complex is detected by the GCE. This scheme is interesting because it combines preconcentration and electrochemical detection. Two linear responses are obtained, one in the concentration range of 5.0?×?10^?11 to 1.6?×?10^?8 M, the other in the range of 1.6?×?10^?8 to 1.42?×?10^?6 M, with a lower detection limit of 1.6?×?10^?11 M. This modified GCE does not suffer from significant interferences by Cu(II), Hg(II), Ag(I), Fe(III), Pb(II), Cr(III), Zn(II), NO^3?, Cl^?, SO ₄ ^2? ions and EDTA. The response of the electrode remained constant for at least 3 weeks of successive operation. The method presented here provides a new way for the simultaneous separation, enrichment, and electrochemical detection of trace cadmium ion.

Sensitive electrochemical determination of Sudan II in food samples using a poly(aminosulfonic acid) modified glassy carbon electrode

In this paper, a novel poly(aminosulfonic acid) modified glassy carbon electrode (PASA/GCE) for the determination of Sudan II was fabricated through electrochemical polymerizat ion. The electrochemical behavior of Sudan II at the modified electrode was studied by cyclic voltammetry. Results show that the modified electrode exhibits excellent electrocatalytic activity toward the electrochemical redox reaction of Sudan II. Under optimal experimental conditions, the oxidation peak current is linearly proportional to the concentration of Sudan II in the ranges of 4.0 × 10^?8 to 1.0 × 10^?6 mol L^?1 and 1.0 × 10^?6 to 1.2 × 10^?5 mol L^?1. The linear regression equations are i _pa(A) = 2.87c + 3.74 × 10^?6, r = 0.9977 and i _pa(A) = 0.78c + 6.11 × 10^?6, r = 0.9982, respectively, and the detection limit is 4.0 × 10^?9 mol L^?1. The novel method shows good recovery, reproducibility and sensitivity for the voltammetric determination of Sudan II in food samples.     

Determination of Trace of Cobalt in Complex Matrices by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10^?10 to 2×10^?8 mol L^?1 and from 1×10^?10 to 1×10^?9 mol L^?1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10^?11 mol L^?1. The interference of high concentrations of foreign ions and surfactants was studied.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Nitrite at an In Situ Plated Bismuth Film Electrode

For the first time an in situ plated bismuth film electrode has been applied to catalytic adsorptive stripping voltammetry of cobalt in the presence of nitrite. At optimised conditions bismuth film was plated before each measurement for 30 s at ?1.0 V from a sample solution with the added supporting electrolyte and Bi(III) in the form of its complex with tartrate. The calibration graph for Co(II) for an accumulation time of 120 s was linear from 5×10^?10 to 1×10^?8 mol L^?1. The detection limit was 1.1×10^?10 mol L^?1. The proposed procedure was applied for Co(II) determination in certified water reference material.     

Determination of 1-hydroxypyrene in human urine by a multi-wall carbon nanotubes-modified glassy carbon electrode

A multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNT-GCE) was used to study the electrochemical behaviour of1-hydroxypyrene (1-OHP) and applied to its determination. The results showed that the modified electrode had a strong adsorptive ability to 1-OHP and enhances its electrochemical signal. By square wave voltammetry, the linear relationship of 1-OHP was 6?×?10^?9???8?×?10^?7?mol?L^?1 with a linear correlation coefficient of 0.996, and the detection limit was 1?×?10^?10?mol?L^?1. Compared with other published methods, this newly proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. And this method was applied successfully in the determination of 1‐OHP in real human urine samples.