Determination of Cysteine in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Abstract

A stripping method for the determination of cysteine in the presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of cysteine at mercury film electrode followed by linear cyclic voltammetry scan measurement of the surface species. Optimum experimental conditions were found to be the use of a 1×10^?3 M NaOH solution, an accumulation potential of ?0.50 V and a scan rate of 200 mV. s^?1. The response of cysteine is linear over the concentration range 0.04–0.20 ppm. For an accumulation time of 15 minutes, the detection limit was found to be 0.9 ppb (7.4×10^?9 M). The more convenient relation to measuring the cysteine in presence of metals, and others amino acids were also investigated. The utility of the method is demonstrated by presence of casein and ATP.     

Adenine Determination in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Highly sensitive, simple and inexpensive techniques of adenine determination are particularly interesting in relation to the present development of ATP and DNA sensors. A nanomolar concentration of adenine can be determined in the presence of copper. For an accumulation time of 30 minutes, the detection limit found was 0.22 ppb (1.63×10^?9 M). The method is based on controlled adsorptive accumulation of adenine‐copper at thin‐film mercury electrode followed by linear scan voltammetric measurement of the surface species. By applying a condition time of 60 s at ?0.9 V, the same thin‐film can be used over several measurements. Optimum experimental conditions were found to be the use of a 5.0×10^?3 M NaOH solution, an accumulation potential over the ?0.20 to ?0.40 V range, and a scan rate of 100 mV s^?1. The response of adenine‐copper is linear over the concentration range 20–100 ppb. The more convenient ways to measuring adenine in the presence of metals and other nitrogenated bases were also investigated. The adenosine triphosphate (ATP) or deoxyribonucleic acid (DNA) are first treated with acid (e.g., 0.1 M perchloric acid), and the acid‐released adenine (without separation from others products of the degradation) is directly determined by adsorptive stripping voltammetry.     

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu²⁺ ions. This electrode was applied for potentiometric and voltammetric detection of Cu²⁺ ion. The potentiometric response of the electrode was linear within the Cu²⁺ concentration range of 3.9 × 10^?6 to 5.0 × 10^?2 M with a near-Nernstian slope of 29.0 mV decade^?1 and a detection limit of 5.0 × 10^?7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10^?8 to 1.0 × 10^?3 M and detection limit was 6.5 × 10^?9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.     

Determination of Trace Copper by Adsorptive Voltammetry Using a Multiwalled Carbon Nanotube Modified Carbon Paste Electrode

A new method for the determination of trace copper was described. A multiwalled carbon nanotube modified carbon paste electrode was prepared and the adsorptive voltammetric behavior of copper‐alizarin red S (ARS) complex at the modified electrode was investigated. By use of the second‐order derivative linear sweep voltammetry, it was found that in 0.04 mol/L acetate buffer solution (pH 4.2) containing 4×10^?6 mol/L ARS, when accumulation potential is 0 mV, accumulation time is 60 s and scan rate is 100 mV/s, the complex can be adsorbed on the surface of the electrode, yielding one sensitive reduction peak at ?172 mV (vs. SCE). The peak current of the complex is proportional to the concentration of Cu(II) in the range of 2.0×10^?11–4.0×10^?7 mol L^?1 with a detection limit (S/N=3) of 8.0×10^?12 mol/L (4 min accumulation). The proposed method was successfully applied to the determination of copper in biological samples with satisfactory results, the recoveries were found to be 96%–102%.     

Cold Deposition as a Novel Procedure for the Preparation of Titania Sol‐Gel: A Development of a High Sensitive Electrochemical Method for Determination of Cu(II) in the Presence of Arsenic(III)

Titania sol‐gel modified gold electrode (TSGMGE) was prepared with the usage of a new proposed cold deposition method at ?10 °C. Scanning electron microscope (SEM) operating at 30 kV was used to obtain micrographs of unmodified and modified electrodes. The obtained results showed that this procedure yields a sol‐gel with high porosity in comparison to conventional methods. The modified Au electrode was fabricated by trapping the L‐glutamine in titania sol‐gel at low temperatures to preparation of a new titania sol‐gel glutamine modified gold electrode (TSGGMGE). The possibility determination of traces of Cu(II) in the presence of As(III) was investigated using proposed electrode. Under the optimized conditions, copper was accumulated at ?0.35 V (vs. Ag/AgCl) for 40 s in 0.1 M acetate buffer (pH 4.0) in the presence of different amounts of arsenic. Two dynamic linear responses with good reproducibility were observed for copper ions in the concentration range of 1 × 10^?6 ?4 × 10^?4 M and 4 × 10^?8 ?6 × 10^?7 M.     

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.     

Adsorptive stripping voltammetry of sex hormones at the static mercury drop electrode

Controlled adsorptive accumulation of testosterone, methyltestosterone and progesterone on the static mercury drop electrode provides the basis for direct stripping measurement of these compounds ar nanomolar concentrations. The adsorptive stripping behavior is evaluated with respect to preconcentration time and potential, stripping mode, concentration dependence, drop size and other variables. With 5-min accumulation, peak current enhancements of 45, 18 anal 12 are observed for 5 × 10^?8 M testosterone, progesterone and methyltestosterone, respectively, relative to direct pulse voltammetry. Detection limits are 1.6 × 10^?10 M for testosterone, 2 × 10^?10 M for progesterone and 3.3 × 10^?10 M for methyltestosterone with 15-min preconcentration. The relative standard deviation for 8 × 10^?8 M progesterone is 3.4% (n=8). Applicability to direct measurements of methyltestosterone in pharmaceutical formulations is assessed.     

Sonoelectroanalytical Detection of Ultra‐Trace Arsenic

The electroanalytical detection of arsenic on a gold electrode is investigated in the presence and absence of ultrasound. It is found that under quiescent conditions a detection limit of 1.8×10^?7 M is achievable using a 120 seconds accumulation period. Applying optimised ultrasound during the accumulation period was found to reduce the limit of detection to 1×10^?8 M from using a deposition period of 60 s at ?0.5 V, while increasing the sensitivity by a factor of 15. The methodology was tested on a river sample containing significant copper contamination and electrode passivating organic materials. This technique provides promise for ‘in the field’ measurements due to the electrode‐depassivating effects of ultrasound.     

Electrochemical studies of determination of C.I. Direct Red 80 based on a gold nanoparticles-modified carbon paste electrode

In this paper, a simple, convenient and sensitive electrochemical method has been developed for the determination of C.I. Direct Red 80. A gold nanoparticle modified carbon paste electrode was fabricated and used for study and sensitive determination of Direct Red 80 by cyclic voltammetry and differential pulse voltammetry. The overall analysis involved a two-step procedure: an accumulation step under open-circuit conditions, followed by voltammetric measurements of Direct Red 80 in a 0.1?M phosphate buffer solution at pH?=?3.0. The experimental conditions, such as the medium, pH and accumulation time, were optimised. The oxidation peak current was proportional to the concentration of Direct Red 80 from 5.0?×?10^?8 to 5.0?×?10^?7?M and 5.0?×?10^?7 to 3.0?×?10^?6?M, and the detection limit was 1.15?×?10^?8?M (S/N?=?3). The proposed method was used to detect Direct Red 80 in natural water and sewage with good accuracy.     

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).     

Novel Copper(II)‐Selective Membrane Electrode Based on a New Synthesized Schiff Base

A PVC membrane electrode for copper(II) ion based on a recently synthesized Schiff base as a suitable ion carrier was constructed. The electrode exhibits a Nernstian slope of 28.3 ± 0.6 mV per decade of Cu²⁺ over a wide concentration range of 7.0 × 10^?6‐2.6 × 10^?2 M with a detection limit of 5.0 × 10^?6M in the pH range of 4.2–5.8. The response time is about 10s and it can be used for at least 1 month without any considerable divergence in potential. It was successfully applied as an indicator electrode in the potentiometric titration of copper ions.     

Stripping voltammetry of thorium based on adsorptive accumulation

A sensitive stripping voltammetric procedure for quantifying thorium is described. The chelate of thorium with the azo dye Mordant Blue 9 is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured during a negative-going potential scan. Cyclic voltammetry is used to characterize the interfacial and redox behaviors. The effects of pH, dye concentration and accumulation potential are discussed. The detection limit is 4 × 10^?10 M (4-min accumulation), a linear current-concentration relationship is observed up to 1.3 × 10^?7 M, and the relative standard deviation (at the 6 × 10^?8 M level) is 3.1%. Possible interferences by trace metals and organic surfactants are investigated. Simultaneous quantitation of thorium and nickel is illustrated.     

Solvent Extraction of Vanadium with α-Benzoin Oxime

The solvent extraction of vanadium by a chloroform solution of α-benzoin oxime was investigated. The most favorable condition for the extraction has been found in the pH rang of 1.8 to 3.0 in sulfate or chloride buffer solutions, but with better extraction efficiency when sulfate was used. A solution of 2×10^?2 M α-benzoin oxime in chloroform was used, and 1×10^?4 to 2×10^?2 M vanadium(V) was extracted favorably in about 89% yield by a single extraction, and in about 97% yield by a double extraction. The effects of shaking time, concentration of α-benzoin oxime, and diverse ions have also been investigated. Vanadium(V) can be readily extracted without interference in the presence of copper(II), aluminum(III), iron(III), silver(I), zirconium(IV), and chromium(III).     

Carbon Paste Electrode Plated with Lead Film. Voltammetric Characteristics and Application in Adsorptive Stripping Voltammetry

A lead film plated in situ at a carbon paste support was tested as a novel, potential electrode for adsorptive stripping voltammetric determination of cobalt traces in an ammonia buffer solution. To show the practical applicability of the new electrode, a catalytic adsorptive Co system in a supporting electrolyte containing 0.1 M ammonia buffer, 5×10^?4 M nioxime and 0.25 M nitrite was selected and investigated as a model solution. Pb and Co ions were simultaneously accumulated in situ on the electrode surface: Pb ions electrochemically at ?1.3 V) and then at ?0.75 V, at which potential the Co(II)‐nioximate complex was also pre‐concentrated via adsorption. Instrumental parameters, such as the time of nucleation and formation of Pb film deposits, the time of accumulation of the Co‐nioxime complex at the PbF/CPE, and the procedures of electrode regeneration, were optimized to obtain good reproducibility and sensitivity of the Co response. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a 5×10^?8 M Co) and good linearity (up to 5×10^?7 M, coefficient of determination, R=0.996). The detection limit was 4×10^?10 M Co (0.023 μg L^?1) for an accumulation time of 120 s. The method enables the determination of Co in the presence of high excesses of Ni or Zn. The voltammetric data were correlated with the structural characterization by scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

Subnanomolar Determination of Indium by Adsorptive Stripping Differential Pulse Voltammetry Using Factorial Design for Optimization

Abstract

A highly sensitive method to determine of indium is proposed by adsorption stripping differential pulse cathodic voltammetry (AdSDPCV) method. The complex of indium ions with xylenol orange is analyzed based on the adsorption collection onto a hanging mercury drop electrode (HMDE). After accumulation of the complex at ?0.20 V vs. Ag/AgCl reference electrode, the potential is scanned in a negative direction from ?0.40 to ?0.75 V with the differential pulse method. Then, the reduction peak current of In(III)–XO complex is measured. The influence of chemical and instrumental variables was studied by factorial design analysis. Under optimum conditions and accumulation time of 60 s, linear dynamic range was 0.1–10 ng/ml (8.7 × 10^?10 to 8.7 × 10^?8 M) with a limit of detection of 0.03 ng/ml (2.6 × 10^?10 M); at accumulation time of 5 min, linear dynamic range was 0.04–10 ng/ml (3.4 × 10^?10 to 8.7 × 10^?8 M) with a limit of detection of 0.013 ng/ml (1.1 × 10^?10 M). The applicability of the method to analysis of real samples was assessed by the determination of indium in water, alloy, and jarosite (zinc ore) samples.     

Adsorptive Stripping Voltammetry of 9‐Phenanthrol in the Presence of Copper at the Static Mercury Drop Electrode—Basis for Quantitative Determination of PAH Metabolite in Biological Materials

Abstract

The electrochemical behavior of 9‐phenanthrol in the presence of copper (II) at a static mercury drop electrode was investigated to provide the basis for development of an inexpensive, sensitive, and reliable method for determination of polycyclic aromatic hydrocarbon (PAH) metabolites in biological matrices. Optimum experimental conditions for analytical applications were obtained in 0.005 M NaOH solution using an accumulation potential of ?0.25 V, a scan rate of 5 mV. s^?1, a pulse height of 25 mV, and a differential pulse scan mode. The response of 9‐phenanthrol is linear over the concentration range 1.0–12.0 ppb. For an accumulation time of 5 minutes, the detection limit was found to be 0.2 ppb (1.03×10^?9 M). The more convenient relation to measure the 9‐phenanthrol in the presence of copper and other metals was also investigated. The utility of the method was demonstrated by the presence of 9‐phenanthrol in samples of sea water and human urine. Cyclic voltammetry was used to characterize the interfacial and redox behavior.     

Determination of traces of palladium by adsorptive stripping voltammetry of the dimethylglyoxime complex

Preconcentration is achieved by adsorption of a palladium-dimethylglyoxime complex on a hanging mercury drop electrode. Optimal conditions area stirred acetate buffer solution (pH 5.15) containing 2 × 10^?4 M dimethylglyoxime and an accumulation potential of —0.20 V. The height of the stripping peak in a negative-going linear scan is linearly dependent on palladium concentration and preconcentration time (over the ranges 0–16 μg l^?1 and 0–300 s, respectively). For a 10-min preconcentration time, the detection limit is 20 ng l^?1 (2.1 × 10^?10 M). Possible interferences by other trace metals are investigated. Palladium added to seawater samples was easily quantified.     

Voltammetric determination of trace amounts of gold(III) with a carbon paste electrode modified with chelating resin

A carbon paste electrode modified with chelating resin (ammino-isopropylmercaptan-type cross-linked chelating resins) for the voltammetric determination of gold(III) was characterized by cyclic voltammetry. The gold(III) ion is accumulated on the surface of the modified electrode only by the chelating effect of the modifier in the carbon paste, without application of a potential. After exchange of the medium the accumulated amount of gold(III) is determined by voltammetry in a blank electrolyte solution. The response depends on both the concentration of gold and the accumulation time. For a 5-min preconcentration time, a linear calibration graph was obtained in the range 3 × 10^?8-1 × 10^?6 M and the detection limit was about 1 × 10^?8 M. A combination of chemical and electrochemical renewal allows the use of a single modified electrode in multiple analytical determinations over several days. For ten preconcentration—determination—renewal cycles [2 × 10^?7 M Au(III)], the response could be reproduced with 4.7% relative standard deviation. Many parameters such as the composition of the paste and pH influence the response of the measurement. Many other metal ions have no or little effect on the determination of gold. The procedure was applied to the determination of gold in minerals, copper and anode mud, with good results.     

Pt‐Nanoparticle Incorporated Carbon Paste Electrode for the Determination of Cu(II) Ion by Anodic Stripping Voltammetry

Pt‐nanoparticles were synthesized and introduced into a carbon paste electrode (CPE), and the resulting modified electrode was applied to the anodic stripping voltammetry of copper(II) ions. The synthesized Pt‐nanoparticles were characterized by cyclic voltammetry, scanning electron microscopy and X‐ray photoelectron spectroscopy techniques to confirm the purity and the size of the prepared Pt‐nanoparticles (ca. 20 nm). This incorporated material seems to act as catalysts with preconcentration sites for copper(II) species that enhances the sensitivity of Cu(II) ions to Cu(I) species at a deposition potential of ?0.6 V in an aqueous solution. The experimental conditions, such as, the electrode composition, pH of the solution, pre‐concentration time, were optimized for the determination of Cu(II) ion using as‐prepared electrode. The sensitivity changes on the different binder materials and the presence of surfactants in the test solution. The interference effect of the coexisted metals were also investigated. In the presence of surfactants, especially TritonX‐100, the Cu(II) detection limit was lowered to 3.9×10^?9 M. However, the Pt‐nanoparticle modified CPE begins to degrade when the period of deposition exceeds to 10 min. Linear response for copper(II) was found in the concentration range between 3.9×10^?8 M and 1.6×10^?6 M, with an estimated detection limit of 1.6×10^?8 M (1.0 ppb) and relative standard deviation was 4.2% (n=5).     

Sensitive Simultaneous Determination of Rutin and Folic Acid with the Use of a Solid Lead Electrode by Means of Adsorptive Stripping Voltammetry

In this article a solid lead electrode (PbE) was utilized for the first time for determination of organic substances by means of adsorptive stripping voltammetry. A new procedure of simultaneous determination of rutin and folic acid was developed. Two well shaped and well separated reduction signals of rutin and folic acid were obtained with the use of PbE. The optimization of analytical procedure was presented. The calibration graphs for rutin and folic acid for an accumulation time of 120 s were linear in the ranges from 2×10^?9 to 1×10^?7 mol L^?1 and from 2×10^?9 to 5×10^?8 mol L^?1, respectively. The obtained detection limits for rutin and folic acid determination following accumulation time of 120 s were 7.9×10^?10 and 8.4×10^?10 mol L^?1. Potential interference effects were investigated. The proposed procedure was used for analysis of pharmaceutical preparations with satisfactory results showing practical applications. The analytical parameters of the proposed procedure were compared with other voltammetric procedures of mentioned substances determination.