Direct determination of selenium in whole blood by anodic stripping voltammetry

Trace quantities of selenium can be determined in the presence of iron, copper and lead using anodic stripping voltammetry, depositing at –0.60 V in 0.1M HClO₄ and stripping in the anodic direction. Two separate peaks are observed at –0.25 V and –0.10 V belonging to copper and selenium, respectively. Sometimes one peak may be observed for both copper and selenium. In this case one more stripping (without deposition) must be done to obtain separate peaks. After standard addition, two strippings have to be done also. With this proposed method, 10^–7 M selenium could be determined as (1.09±0.03) × 10^–7 M with a 90% confidence interval in blood samples without any separation.Presented at Xth National Chemistry Congress, Bursa, Turkey, September 19–21, 1994     

Metal analysis in real matrices. Simultaneous voltammetric determination of copper and antimony in alloys

This work addresses the simultaneous determination of copper(II) and antimony(III) in real matrices by differential pulse (DPASV) and fundamental harmonic alternating current anodic stripping voltammetry (ACASV). The voltammetric measurements were carried out using as supporting electrolyte the same acidic mixture (nitric, hydrochloric and perchloric acids) used in the dissolution of the real matrices with proper dilution. The procedure of the sample preparation is thus reduced to one step hence avoiding errors from long and complex sample handlings prior to the instrumental measurement. The results were verified by the analysis of the standard reference materials NBS-SRM 631 Spectrographic Zinc Spelter D-2 and BCS 207/2 Gunmetal. The precision, expressed as relative standard deviation, and the accuracy, expressed as relative error, were, in all cases, less than 5%; the detection limit, for each element and in the experimental conditions employed, was around 10⁻⁷ M. The standard addition technique improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.     

Determination of Cd(II) in Some Foodstuffs by Anodic Stripping Pulse Voltammetry (ASPV) using Glassy Carbon Electrode

Abstract

Cadmium in the presence of 0.04 M NaCl as the electrolyte was determined using stripping voltammetry with superimposed constant amplitude pulses of negative polarity (SVPNP) or positive polarity (SVPPP), and differential pulses stripping voltammetry using rotating disc glass carbon electrode (RDGCE). The SVPNP was found to give the greatest sensitivity. The anodic peak was obtained at potential ?850 to ?795 mV due to the oxidation of cadmium to cadmium(II). Linear calibration curves were obtained in the concentration range between 1.5×10^?9–2×10^?10 M. The relative standard deviation is 4.25% at very low concentration of 2×10^?10 M. This method was successfully applied to the determination of cadmium in some foodstuffs (wheat and its products, vegetables) after acid digestion.     

Palladium Particles‐Impregnated Natural Phosphate Electrodes for Electrochemical Determination of Mercury in Ambient Water Samples

We present here a simple procedure for the determination of mercury(II) using differential pulse anodic stripping voltammetry (DPASV) at palladium particles‐impregnated natural phosphate modified carbon paste electrodes (Pd‐NP‐CPE). The surface of modified electrode was characterized using SEM, infrared spectroscopy, X‐ray diffraction and electrochemical analysis. All experimental variables involved in the voltammetric stripping method were optimized. The detection limit was found to be 4.99×10^?8 mol L^?1 (S/N=3) that is not different to the permitted value for Hg(II) in water reported by the Environmental Protection Agency (EPA). The proposed electrode exhibits good applicability for monitoring Hg(II) in tap and wastewater.     

Integrated gold-disk microelectrode modified with iron(II)-phthalocyanine for nitric oxide detection in macrophages

An integrated gold-disk microelectrode (IGME) was fabricated and modified with Fe(II)-phthalocyanine (Fe(II)-PC) for NO detection in biological media. Microanalysis of NO using square wave anodic stripping voltammetry (SWASV) in 0.01 M HClO₄ was optimal at the initial potential of 0.1 V, frequency of 100 Hz, pulse amplitude of 25 mV, and a scan rate of 200 mV/s. When the electrode was modified with Fe(II)-phthalocyanines, the anodic peak current and sensitivity of NO were remarkably increased due to the catalytic oxidation of NO. The calibration curve had good linearity in the range from 3.6×10⁻⁵ to 7.2×10⁻⁷ M, and the detection limit was (5.7±1.2)×10⁻⁷ M. Fe(II)-phthalocyanine modified gold-disk microelectrode coated with Nafion was applied to determination of NO released from macrophage cell.     

Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10^–6–1×10^–4, 2×10^–7–1×10^–4, 1×10^–8–1×10^–4 and 2×10^–9–1×10^–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10^–10 M (drinking water) and 3×10^–9 M (river water).     

Evaluation of a carbon paste electrode modified with organofunctionalized amorphous silica in the cadmium determination in a differential pulse anodic stripping voltammetric procedure

The determination of cadmium using a carbon paste electrode modified with organofunctionalized amorphous silica with 2-benzothiazolethiol was investigated. The Cd(II) oxidation peak was observed around −0.80 V (vs. SCE) in phosphate buffer (pH 4.0) in differential pulse anodic stripping voltammetry. The best results were obtained under the following optimized conditions: 1 min accumulation time, 50 mV pulse amplitude, 20 mV s⁻¹ scan rate in phosphate buffer pH 4.0. Using such parameters a linear dynamic range from 5.6×10⁻⁷ to 3.5×10⁻⁵ mol l⁻¹ Cd(II) was observed with a sensitivity of 2.83 μA mol⁻¹ l, limit of detection 1.0×10⁻⁷ mol l⁻¹. Cd(II) spiked in a natural water sample was determined with 99% mean recovery at 10⁻⁷ mol l⁻¹ level. Interference were also evaluated.     

Determination of Copper(II) Through Anodic Stripping Voltammetry in Tartrate Buffer Using an Antimony Film Screen-printed Carbon Electrode

The voltammetric performance of an in situ plated antimony film screen-printed carbon electrode in hydrochloric acid, acetate buffer, and tartrate buffer was evaluated for the detection of copper(II) with differential pulse anodic stripping voltammetry. The tartrate buffer was superior, providing high sensitivity and good separation of copper and antimony stripping peaks. The analytical conditions for the determination of copper(II) were optimized. The detection limit was estimated to be 0.14?µg?L^?1 copper(II) and the relative standard deviation for 2.5?µg?L^?1 copper(II) was 3%. The applicability of the method was illustrated by the analysis of soil conditioner samples.     

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low μg l⁻¹ concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at −1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from −1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 μg l⁻¹ for Cd and for Pb and 0.7 μg l⁻¹ for Zn at a preconcentration time of 10 min. Finally, BFE's were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).     

Thiol‐Functionalized Silica Thin Film Modified Electrode in Determination of Mercury Ions in Natural Water

The use of a thin thiol‐functionalized silica film modified glassy carbon electrode in the determination of Hg(II) ions in a natural water sample is described. A typical measurement involves two successive steps: a glassy carbon electrode coated with a thin mesoporous silica film containing 10% of mercaptopropyl groups, according to the MPTMS/TEOS ratio in the starting sol‐gel, was first immersed into the accumulation medium for 15 min, then removed, and finally transferred into a detection solution containing KCl 1.0 mol L^?1 where detection was performed by anodic stripping voltammetry. In this medium the previously accumulated Hg²⁺ species complexed by the thiol groups in an open circuit preconcentration step is then directly reduced at ?0.6 V during 60 s prior to be quantified by a differential pulse anodic scan from ?0.6 to 0.3 V (vs. Ag/AgCl). A stripping peak appeared at about ?0.01 V, which is directly proportional to the quantity of the analyte previously accumulated into the film. The best results were obtained under the following conditions: 100 mV pulse amplitude and 10 mV s^?1 scan rate in 1.0 mol L^?1 KCl solution pH 2.0. Using such parameters a linear dynamic range from 1.00 to 10.0×10^?8 mol L^?1 Hg(II) was observed with a limit of detection of 4.3 nmol L^?1 for an accumulation time of 15 min. Hg(II) spiked in a natural water sample was determined between 97.0 and 101.4% mean recovery at 10^?8 mol L^?1 level. The results indicate that this electrode is sensitive and selective for the Hg(II)determination.     

Studies on substituted phenols by differential pulse cathodic stripping voltammetry: 1. Pentachlorophenol

A study of chlorophenols using differential pulse cathodic stripping voltammetry (dpcsv) is reported. Of the wide range of chlorophenols investigated, only pentachlorophenol and 2,3,4,6-tetrachlorophenol yield stripping peaks.For pentachlorophenol in water, two peaks are obtained at stripping potentials of –1.2 V and –1.58 V versus SCE. In methanol, pentachlorophenol shows one peak with a stripping potential at –1.6 V versus SCE.In the case of 2,3,4,6-tetrachlorophenol in water, two peaks are observed at –1.06 V and –1.6 V versus SCE, while in methanol only one peak arises at a stripping potential of –1.6 V. A procedure was developed for the determination of pentachlorophenol in natural waters.     

Determination of Se, As, Cu, Pb, Cd, Zn and Mn by anodic and cathodic stripping voltammetry in marine environmental matrices in the presence of reciprocal interference. Proposal of a new analytical procedure

Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II), zinc(II) and manganese(II) have been determined in environmental matrices by differential pulse cathodic (DPCSV) and anodic (DPASV) stripping voltammetry. The voltammetric measurements were carried out using a conventional three-electrode cell and the ammonia–ammonium chloride buffer (pH 9.4) as the supporting electrolyte. The analytical procedure was verified by the analysis of the standard reference materials: Sea Water BCR-CRM 403; Lagarosiphon Major BCR-CRM 060; and Cod Muscle BCR-CRM 422. The precision, expressed as relative standard deviation, and the accuracy, expressed as relative error, were, in all cases, lower than 5%; the detection limits, for each element in the experimental conditions employed, was approximately 10⁻⁹ M. The standard addition technique significantly improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.     

Sensitive,Accurate and Selective Determination of Cd(II) Using Anodic Stripping Voltammetry with in-situ Hg-Bi Film Modified Pencil Graphite Electrode After Magnetic Dispersive Solid Phase Microextraction

This paper describes a novel approach to detect Cd(II) using the combination of the differential pulse anodic stripping voltammetry and magnetic nanoparticle based dispersive solid phase microextraction as an efficient, green and accurate method. Currents of Cd(II) increased linearly in the range from 75 to 2000 ng L⁻¹ Cd(II) with a detection limit of 21.6 ng L⁻¹. The RSD values of 2.6 and 6.0 % for 1.00 and 0.10 μg L⁻¹ respectively showed that proposed method has an acceptable repeatability. Recovery values between 92.3 and 98.6 % showed that this approach can be successfully used for determination of Cd(II) in water samples.     

Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode

The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l^–1 NH₃-NH₄Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH₃-NH₄Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml^–1 to 50.0 g ml^–1. The detection limit (three times the signal-to-noise) was 1.0 g ml^–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml^–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

Determination of inorganic antimony species in seawater by differential pulse anodic stripping voltammetry: stability of the trivalent state

A simple method is described for the rapid and reliable determination of ultratrace concentrations of Sb(III) and Sb(V) in seawater by differential pulse anodic stripping voltammetry. It is based on the well-known dependence of Sb(III)/Sb(V) voltammetric response on acidity conditions. Under our optimised conditions (0.5 mol l⁻¹ HCl for Sb(III) and 5 mol l⁻¹ HCl for total Sb, respectively): (i) a detection limit of 11 ng l⁻¹ is obtained for a 10 min deposition time; (ii) no prior elimination of organic matter is needed; and (iii) antimony can be determined in the presence of natural copper levels. Particular care has been taken in order to understand the chemical processes taking place in all the solutions and reactions involved in the sampling and measuring procedures. Our results revealed the need to consider (i) the effect of photooxydation of synthetic and seawater samples on Sb speciation; and (ii) the stability of Sb(III) both in seawater samples and in the analytical solutions.     

Indirect determination of lutetium by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode

Lutetium has been determined by differential pulse anodic stripping voltammetry in an acidic solution containing Zn-EDTA. Lutetium (III) ions liberated zinc (II), which was preconcentrated on a hanging mercury drop electrode and stripped anodically, resulting in peak current linearly dependent on lutetium (III) concentration. Less than 0.4 ng mL⁻¹ lutetium could be detected after a 2 min deposition.      

Ultra-Sensitive Anodic Stripping Voltammetry for the Determination of Xanthine at a Glassy Carbon Electrode

An electrochemical anodic stripping procedure for ultra-trace assay of xanthine in Cu²⁺ solution at a glassy carbon electrode (GCE) is described. Cyclic voltammetry was used to characterize the nature of the process taking place at the GCE. The anodic stripping response in the presence of Cu²⁺, at 150mV (peak I) and 600mV (peak II), is evaluated with respect to various experimental and instrumental conditions. Voltammetric studies show that the mechanism of the overall reaction is similar to that of the oxidation of purine derivatives at a pyrolytic graphite electrode. It is found that the copper metal deposited onto the GCE was oxidized to Cu⁺ at around –180mV vs. Ag/AgCl and the generated Cu⁺ reacted with xanthine to accumulate on the GCE as an insoluble compound. The Cu⁺-xanthine compound accumulated on the GCE was redissolved by the oxidation of Cu⁺ to Cu²⁺ at ca. 150mV, and the concentration of xanthine in the vicinity of the GCE increased. The results enabled us to use the measurement of the oxidation peak current as the basis of a simple, accurate and rapid method of determining xanthine within a concentration range of 19.9 to 166nM for peak (I) and 0.24 to 17.2µM for peak (II). Promising results were obtained for xanthine determination by using an external mixing step prior to stripping measurements, which yielded a detection limit of 0.138µgL^–1 (9.1×10^–10M) xanthine. The effect of some interferences (e.g. purine compounds, amino acids and some metal ions) was considered.     

Application of a Carbon Nanotube Modified Electrode in Anodic Stripping Voltammetry for Determination of Trace Amounts of 6-Benzylaminopurine

Carbon nanotubes were modified on the surface of a glassy carbon electrode (GC) and initially applied in semi-derivative anode stripping voltammetry for the determination of 6-benzylaminopurine. The experiments demonstrated that the presence of the carbon nanotube greatly increased the current of the oxidation peak of benzylaminopurine. Cyclic voltammetry (CV) and semi-derivative voltammetry were used in a comparative investigation into the electrochemical oxidation of benzylaminopurine with the modified electrode. Studies on the effect of pH on the peak current and potential were carried out over the pH range of 9.013.0 with the NH₃–NH₄Cl buffer solution. A pH of 10.0 was chosen as the optimum pH. Other experimental parameters, such as film thickness, accumulation potential, temperature etc. were optimized. The anodic peak current was found to be linearly related to the concentration of benzylaminopurine over the range of 4.0×10^–8 to 1.0×10^–5mol·L^–1 with a detection limit of 5.0×10^–9mol·L^–1 in an accumulation time of 5min. Interferences of some inorganic and organic species on the response have been studied.     

New Strategies for the Simple and Sensitive Voltammetric Direct Quantification of Se(IV) in Environmental Waters Employing Bismuth Film Modified Glassy Carbon Electrode and Amberlite Resin

An analytical procedure regarding the determination of selenium(IV) by anodic stripping voltammetry exploiting the in situ plated bismuth film electrode is described. Since organics are commonly present in untreated natural water samples, the use of Amberlite XAD-7 resin turns out to be quite important to avoid problems such as the adsorption of these compounds on the working electrode. The optimum circumstances for the detection of selenium in water using differential pulse voltammetry techniques were found to be as follows: 0.1 mol L⁻¹ acetic acid, 1.9 × 10⁻⁵ mol L⁻¹ Bi(III), 0.1 g Amberlite XAD-7 resin, and successive potentials of −1.6 V for 5 s and −0.4 V for 60 s, during which the in situ formation of the bismuth film on glassy carbon and the accumulation of selenium took place. The current of the anodic peak varies linearly with the selenium concentration ranging from 3 × 10⁻⁹ mol L⁻¹ to 3 × 10⁻⁶ mol L⁻¹ (r = 0.9995), with a detection limit of 8 × 10⁻¹⁰ mol L⁻¹. The proposed procedure was used for Se(IV) determination in certified reference materials and natural water samples, and acceptable results and recoveries were obtained.