Stripping Voltammetric Analysis Research Articles

Content of heavy metals in the hair

The aim of our investigation was to determine of HM content in the hair of people and animals. Two of the main essential elements- Zn and Cu and two of the supertoxical heavy metals- Pb and Cd were chosen. The investigations were conducted in Russian Federation and Belarus Republic in 2001- 2002. About 500 hair samples of people, dogs, cats, cattle, horses, yaks, pigs, sheep goats and rabbits were studied by the stripping voltammetric analysis (SVA) method with TA- 2 analyzer to determine Zn, Cu, Pb and Cd concentrations. The hair samples were prepared according to the methods developed in Tomsk University (Russia) and improved by the authors. The essence of the methods is the multiconsecutive burning of hair samples to ashes and boiling them in concentrated acids to dissolve chemical combinations and transform their metals into ion forms. The zinc concentration was the highest in all hair samples (58.65... 195.15 mg/kg). The copper content was several times less (5.49... 22.63 mg/kg). Lead and cadmium were detected in relatively low amounts (0.32... 2.42 mg/kg and 0.04... 0.92 mg/kg respectively). The highest Pb and Cd levels were detected in cats and people hair.

Imprinted Polymer – Modified Hanging Mercury Drop Electrode for Differential Pulse Adsorptive Stripping Voltammetric Analysis of a Diquat Herbicide

AbstractAn imprinted polymer modified hanging mercury drop electrode (HMDE) in Model 303A system in conjunction with a PAR Model 264A Polarographic Analyzer/Stripping Voltammeter has been used for the selective analysis of a diquat herbicide viz., 5,6‐dihydropyrazino[1,2,3,4‐[lmn]‐1,10‐phenanthrolinium dichlorides in differential pulse cathodic stripping voltammetry mode. Complex aqueous samples (drinking water and agricultural soil suspension), spiked with a diquat herbicide, were directly analyzed by the adsorptive accumulation of the analyte over the working electrode (accumulation potential −0.8 V (vs. Ag/AgCl), accumulation time 120 s, pH 7.0, supporting electrolyte 0.1 M KCl, scan rate 10 mV s−1, pulse amplitude 25 mV). The limit of detection for diquat herbicide was found to be 0.34 nmol L−1 (0.1 ppb, RSD 2%, S/N=2).

Bismuth-film-plated carbon paste electrodes

In this preliminary note, carbon paste electrodes (CPEs) plated with a bismuth film are presented. The bismuth film can be generated onto the carbon paste surface either from an external plating solution or in situ; the latter being performed in two ways: (i) as a spike of the Bi 3+ ions to the solution or (ii) via modifying the carbon paste with solid bismuth oxide (5% m/m). As shown on selected examples, bismuth-film-plated CPEs exhibit a good performance in voltammetric stripping analysis of some heavy metals such as Pb, Cd, and Zn.

Screen-printed anodic stripping voltammetric sensor containing HgO for heavy metal analysis

A screen-printed disposable sensor for the anodic stripping voltammetric (ASV) analysis of heavy metals was prepared by integrating a HgO-modified working electrode, Ag/AgCl reference electrode, and carbon counter electrode on a polycarbonate strip. The working electrode was screen-printed with phenol resin-based carbon ink containing fine particles of mercuric oxide as a built-in mercury precursor. The mercuric oxide particles exposed on the surface were reduced to fine mercury droplets by in situ or pre-cathodic conditioning in order to allow them to behave as heavy metal collectors in the anodic stripping analysis. The reference and counter electrodes were also screen-printed using commercial silver paste ink modified with finely ground AgCl powder and commercial carbon ink, respectively. The analytical characteristics of the sensor were evaluated using Pb and Cd as probe metals. Detailed preparation procedures and analytical characteristics of the sensor are described.

Transport, Fate and Speciation of Heavy Metals (Pb, Zn, Cu, Cd) in Mine Drainage: Geochemical Modeling and Anodic Stripping Voltammetric Analysis

The maximum concentrations (ppb) of heavy metals in the mine drainage (pH: down to 3.3) of Chonam-ri creek in the abandoned Kwangyang gold-silver mine, South Korea, are 22600 Zn, 2810 Cu, 182 Cd, and 109 Pb. A small, limestone-infused retention pond, about 440 meters downstream from the waste dump, plays an important role in the removal of heavy metals: the factors of reduction for Zn, Cu, Cd, and Pb are 12, 24, 14, and 14, respectively. This is due to the pH increase (up to >5.4) accompanying adsorption onto and/or coprecipitation with Fe- and Al-hydroxides (goethite and gibbsite). From the waste dump to the pond, heavy metal concentrations also progressively decrease due to pH increase. Geochemical modeling (using the computer code WATEQ4F) predicts that free aqueous metal ions are dominant (mostly >70% for Cu and Zn, and >60% for Pb and Cd) in samples collected upstream from the pond, whereas complexing with sulfate, carbonate and hydroxyl ions becomes important in the samples collected downstream. The comparison between the concentrations of electrochemically labile species (determined by Anodic Stripping Voltammetry) and the result of computer modeling shows that Cd and Zn are present predominantly as labile inorganic species throughout the whole range of the creek. However, Cu and Pb in the samples collected downstream from the pond largely form electrochemically inert species (possibly, metal-organic complexes). The above results indicate that the retention pond is effective in reducing the toxicity of heavy metals, especially Cu and Pb.

Long-lived sensors with replaceable surface for stripping voltammetric analysis: Part I

This study was inspired by the need of solving main problems of stripping voltammetry involving a short lifetime of electrodes, the necessity of mechanical regeneration of their surface and toxicity of mercury. The proposed electrodes (sensors) consist of a tungsten wire or a carbon-containing filament (thread). The latter was modified using one of the following methods: electroplating with mercury “in situ” or beforehand, or deposition of an insoluble mercury-organic complex on the filament surface beforehand and electrochemical reduction of the complex during analysis. Rotating disk tungsten electrodes, impregnated graphite disk electrodes and thick-film graphite electrodes were used to choose the solution composition and potential waveforms, and to compare the efficiency of the proposed sensor and earlier sensors. It was shown that long-lived mercury-free tungsten electrodes may serve to determine copper ions over the concentration interval from 10 to 1000 μg l −1. The carbon-containing filament may be used to determine copper, lead and cadmium concentrations at the level of μg l −1. A total of 10 measurements can be made using one and the same section of the electrode. Relative standard deviations of concentrations found range from 0.026 to 0.14 for various versions of electrodes and concentration intervals. The lifetime of the sensor is determined by the length of the wire or the thread and the replacement frequency of the working section. The obtained data confirm the reliability of the long-lived sensors. All the sensors, except the carbon-containing filament modified “in situ”, do not contaminate the environment with mercury. The long-lived sensors can be installed in flow-through systems designed for use under laboratory conditions and for remote unattended environmental monitoring.

Small‐size sensors for the in‐field stripping voltammetric analysis of water

AbstractSensors based on thick‐film graphite and screen‐printed electrodes open up a new era in stripping voltammetry. The increasing application of the stripping analysis in laboratory, field, and on‐line variants is expected in the near future. The use of modified thick‐film graphite and screen‐printed electrodes allows solving main problems of the method: toxicity of mercury and mechanical regeneration of the solid electrode surface. However, one of the problems with the stripping voltammetric method, namely the interference of organic compounds, cannot be solved without sample pretreatment. New four‐electrode sensors based on thick‐film graphite and screen‐printed carbon electrodes for analysis of natural and waste waters are described. The analysis is performed in three steps: sample pretreatment, accumulation of the analyte on the electrode surface, and measurement. The measuring cells have a small volume (e.g., 0.2–0.8 ml) sufficient for uniform mixing of the test solution and introduction (if required) of standard additions. A solid electrolyte can be placed in the cell. The sensors were used for determination of Cu, Pb, and Cd concentrations. The detection limit is n × 10−7 g l−1. Some results of the analysis of model solutions, river and waste waters with the use of the standard addition method or calibration curves are given. © 2002 Wiley Periodicals, Inc. Field Analyt Chem Technol 5: 260–271, 2001; DOI 10.1002/fact.10006

Application of orthogonal functions to differential pulse voltammetric analysis: Simultaneous determination of tin and lead in soft drinks

The application of two-component analysis methods, differentiation of signals and orthogonal function, to the resolution of partially overlapping differential pulse voltammetric (DPV) peaks is demonstrated. The study was extended to differential pulse cathodic stripping voltammetry (DPCSV). A binary system of tin(II) and lead(II), having 72 mV of DPV peaks separation in 0.04 M acetic/ o-phosphoric/boric acids’ mixture, was used as a model throughout the work. The stripping voltammetric analysis data processed by orthogonal functions and the first-derivative ( 1D) methods, were successfully applied to the simultaneous determination of both metals in canned soft drinks. Moreover, the applicability of the methods were demonstrated by the recovery of lead in a drinking water sample.

Atmospheric SO2 Determination by Voltammetric Analysis at an Iodine-Coated Platinum Electrode

An indirect method for determination of atmospheric sulfur dioxide was developed and tested. Air samples were collected in 30 % H2O2 solution which converts SO2 to SO42–. The sampling technique is the same technique used in the thorin spectrophotometric method for analysis of sulfur dioxide. The developed method, however, relied on voltammetric analysis of Pb(II) upon addition of an excess Pb(II) solution. The excess Pb(II) was determined by linear sweep anodic stripping voltammetric analysis at an iodine-coated polycrystalline platinum electrode. The electrode iodination was carried out from the gas phase. The calibration plot from cyclic voltammetric measurements of the cathodic deposition peak current and the Pb(II) concentration showed a remarkable linearity between the peak current and Pb(II) concentration (correlation coefficient=0.9994). Stripping analysis of Pb(II) at the iodine-coated electrode showed better sensitivity and excellent linearity between the anodic stripping peak current and the concentration of Pb(II) (correlation coefficient=0.9934). Application of voltammetric analysis for the indirect determination of SO2 also showed remarkable linearity and a sensitivity not less than that of the thorin method (R = 0.9993). The developed method passed the recovery and real-life analysis tests.

Atmospheric SO2 Determination by Voltammetric Analysis at an Iodine-Coated Platinum Electrode

An indirect method for determination of atmospheric sulfur dioxide was developed and tested. Air samples were collected in 30 % H2O2 solution which converts SO2 to SO42–. The sampling technique is the same technique used in the thorin spectrophotometric method for analysis of sulfur dioxide. The developed method, however, relied on voltammetric analysis of Pb(II) upon addition of an excess Pb(II) solution. The excess Pb(II) was determined by linear sweep anodic stripping voltammetric analysis at an iodine-coated polycrystalline platinum electrode. The electrode iodination was carried out from the gas phase. The calibration plot from cyclic voltammetric measurements of the cathodic deposition peak current and the Pb(II) concentration showed a remarkable linearity between the peak current and Pb(II) concentration (correlation coefficient=0.9994). Stripping analysis of Pb(II) at the iodine-coated electrode showed better sensitivity and excellent linearity between the anodic stripping peak current and the concentration of Pb(II) (correlation coefficient=0.9934). Application of voltammetric analysis for the indirect determination of SO2 also showed remarkable linearity and a sensitivity not less than that of the thorin method (R = 0.9993). The developed method passed the recovery and real-life analysis tests.

Estimating crystal quality in semiconductors using voltammetry

A voltammeter can be used to differentiate the crystalline quality of the compound semiconductor, lead–tin–telluride. A modified differential pulse stripping voltammetric analysis procedure is used with a millimolar bromine/bromide etchant. Higher quality crystals, which had been grown using a magnetically damped Bridgman technique, required longer times for the onset of etching, had smaller rates of etching, and attained smaller depths of etching than did poorer quality crystals grown without magnetic dampening. This analysis procedure is faster, more amenable to quantitative results, and much safer than traditional etching techniques, which use highly corrosive chemicals. The results of the voltammetric analysis were verified using a standard Norr etch in a traditional electrochemical etching procedure and counting dislocation densities.

Voltammetric stripping analysis of metal concentrates with polymers soluble in aqueous solutions

The conditions were worked out for the simultaneous stripping voltammetric determination of components of the ternary Pb(II)-Cu(II)-Cd(II) and binary Ag(I)-Cu(II) systems at a carbon-paste electrode in 2% aqueous solutions of the water soluble polymer polyethyleneimine (PEI) and its thiourea-containing derivative (TU-PEI). Water-soluble polymers are shown to reduce the mutual effects of the components of the binary and ternary system at the electrode surface. The different complex stability of Ag(I), Pb(II) or Cd(II) and Cu(II) with PEI and TU-PEI allows Ag(I), Pb(II) and Cd(II) to be determined in the presence of a large excess of Cu(II).

Adsorptive Stripping Voltammetry in the Presence of Power Ultrasound: The Detection of Vanadium in Aqueous Media

The first study of ultrasound-assisted adsorptive stripping voltammetry (AdSV) is reported. Power ultrasound emitted from a titanium horn probe placed opposite a working electrode in a conventional three electrode cell was applied during the preconcentration step of the adsorptive stripping voltammetric analysis of a vanadium-catechol complex at a mercury-plated copper electrode. Ultrasound was found to significantly improve the sensitivity of the procedure by increasing the rate at which the complex was deposited onto the mercury surface in comparison with silent conditions. The adsorption appeared to follow a Langmuir isotherm.

Rotating Sample System: An Equivalent of a Rotating Electrode for Microliter Samples

Voltammetric experiments in sample droplets of 20 microL volume were carried out with gold ring electrodes microfabricated on Pyrex substrates. The droplet studied was centered and kept in place by a hydrophobic ring deposited on the substrate around the ring electrode, which also ensured that each sample assume a semispherical shape. A small hole in the center of the substrate filled with an agar gel membrane served as a junction. A mild jet of humidified nitrogen gas directed tangentially at the droplet caused it to rotate at a high rate. Cyclic voltammetry and constant-potential electrolysis of potassium ferricyanide were used to characterize this rotating sample system and to calculate diffusion layer thickness. The results clearly demonstrate that rotating of a semispherical microsample placed above a stationary ring electrode with a mild gas jet can be as effective as a rotating electrode system. As a practical example, voltammetric stripping analysis of 20-120 pmol mercuric nitrate samples was performed with a calibration of good linearity (r2 = 0.988) and a time constant for exhaustive electrolysis of approximately 2 min.

Square‐wave voltammetric stripping analysis of thallium(III) at a poly(4‐vinylpyridine)/mercury film electrode

AbstractA poly(4‐vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square‐wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion‐exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface‐active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.

Square-wave voltammetric stripping analysis of lead(II) at a Nafion ®/copper-mercury film electrode

A novel Nafion ®/copper-mercury film electrode was developed for the determination of trace Pb(II) in real samples by square-wave anodic stripping voltammetry. The preparation of the Nafion ®/copper-mercury film electrode was performed by first spin-coating the Nafion ® polymer on the glassy carbon electrode surface. Subsequently, an appropriate molar concentration ratio of Cu(II) to Hg(II) was plated onto the electrode. Various factors influencing the determination of Pb(II) were thoroughly investigated. Under optimal conditions, compared with a conventional Nafion ®/mercury film electrode, a 4-fold increase in sensitivity can be achieved. Linear calibration curves are obtained over the 0–20 μg 1 −1 range with a detection limit of 80 ng 1 −1 ( S N = 3 ) for 150 s preconcentration time. The Nafion ®/copper-mercury film electrode showed good resistance to interferences from surface-active compounds and common ions. High precision is achievable, if the copper mercury film is preplated freshly before each analysis. The analytical utility of the Nafion ®/copper-mercury film electrode was demonstrated by application to various water samples.

Epoxy−Graphite Tube Bulk-Modified with 2-Mercaptobenzothiazole as a Robust Electrode for the Preconcentration and Stripping Analysis of Hg(II)

A novel method of fabricating a bulk-modified composite electrode is proposed. In this method, a preformed, porous graphite tube was impregnated with a modifier by thorough soaking in a solution containing the modifier. After drying, the modifier was sealed in place in the pores with epoxy. For the purpose of demonstrating the usefulness of the electrode, 2-mercaptobenzothiazole was chosen as the modifier and the modified electrode was used to preconcentrate mercury(II), followed by voltammetric stripping analysis. The fabricated electrode possessed good stability and had an extended lifetime. Precision for 10 consecutive differential pulse stripping experiments, for a 2 min preconcentration, gave relative standard deviations of 1.9% and 2.6% for Hg(II) concentrations of 1.00 × 10-6 and 1.00 × 10-8 M, respectively. Detection limit was estimated to be 3.0 × 10-9 M (S/N = 3, 3 min preconcentration). A certified aqueous sample, USEPA WP 386, was employed for method testing.

Ultrasonic extraction and field‐portable anodic stripping voltammetry of lead from environmental samples

AbstractUltrasonic extraction of lead from environmental samples, followed by anodic stripping voltammetric (ASV) analysis using a field‐portable ASV instrument, was evaluated. Representative lead‐containing standard reference materials were subjected to ultrasonic agitation in dilute nitric acid, and the lead subsequently determined by ASV. Recoveries of lead were found to be statistically equivalent to those obtained previously by means of hotplate concentrated acid digestion and atomic spectrometric analysis. Laboratory‐prepared air filter samples were also analyzed for lead content by using the ultrasonic extraction/portable ASV analytical protocol. For duplicate laboratory‐prepared air filter samples, results from microwave digestion and atomic absorption analysis compared well with those from ultrasonic extraction and portable ASV analysis. The lower detection limit for the ultrasound/portable ASV method was found to be less than 1 ppb Pb in solution, or < 0.1 μg Pb/filter. The results suggest that the method may allow for the on‐site determination of lead in environmental samples such as paint, dust, soil and workplace air.

Effect of model organic compounds on square-wave voltammetric stripping analysis at the Nafion/chelating agent mercury film electrodes

The effect of various organic compounds on the Nafion/chelating agent mercury film electrodes (NCAMFEs) in square-wave anodic-stripping voltammetry (SWASV) is explored. Two chelating agents used to prepare the NCAMFEs are dimethylglyoxime and 2,2'-bipyridyl. Triton X-100, sodium dodecyl sulfate, albumin, gelatin, starch, camphor, and humic acid are used as model organic compounds, while cadmium, lead, and copper are used as test metal ions. The NCAMFEs are considerably more resistant to organic interferences than the Nafion-coated mercury film electrode. The implications of these interferences for the reliability and feasibility of stripping measurements using the NCAMFEs in real samples are discussed. Results presented for untreated urine and natural water samples demonstrate the analytical utility of the NCAMFEs in SWASV.

Individual and simultaneous determination of zinc and cadmium in biological tissues by flow injections / stripping voltammetric analysis

AbstractA flow‐injection (FI) voltammetric‐stripping method for the simultaneous determination of Cd and Zn is proposed after a systematic study of the variables affecting the method. The low determination limits, 1 × 10−9 and 5 × 10−9 M (detection limits 8 × 1010– and 2 × 10−9 M for Cd and Zn, respectively), and rsd. values, 1.57 and 5.16% for Cd and Zn, respectively, allow one to apply the method to real samples (biological tissues and reference materials) with good results. No formation of intermetallic compounds was detected.