Stripping voltammetry in environmental and food analysis

The review covers over 230 papers published mostly in the last 5 years. The goal of the review is to attract the attention of researchers and users to stripping voltammetry in particular, its application in environmental monitoring and analysis of foodstuffs. The sensors employed are impregnated graphite, carbon paste, thick film carbon/graphite and thin film metallic electrodes modified in-situ or beforehand. Hanging mercury drop electrodes and mercury coated glassy carbon electrodes are also mentioned. Strip and long-lived sensors for portable instruments and flow through systems are discussed as devices for future development and application of stripping voltammetry. Received: 30 March 2000 / Revised: 30 May 2000 / Accepted: 6 June 2000     

Trace analysis by polarography and voltammetry in pharmaceutical and environmental chemistry

Differential pulse polarography (d.p.p.), anodic and cathodic stripping voltammetry (a.s.v. and c.s.v.) and on-line electrochemical detection (e.g., HPLC-e.d.) have been extensively exploited in recent years for the determination of trace concentrations of many organic and organometallic molecules of biological significance. Such analyses can be carried out in complex matrices such as body fluids, foods, agricultural materials and aquatic matrices^1,2,3.     

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.     

Stripping voltammetry at micro-interface arrays: A review

In this article, a comprehensive overview of the most recent developments in the field of stripping voltammetry at regular micro-interfaces (both solid–liquid and liquid–liquid interfaces) is presented. This review will report on the most conventional arrays of metallic micro-electrodes but also on the rapidly growing field of electrochemistry at arrays of micro-interfaces between two immiscible electrolyte solutions (μITIES). The main fabrication methods, together with some design considerations and diffusion phenomena at such interfaces are discussed. Main applications of micro-interface arrays are presented including heavy metals detection at micro-electrode arrays and detection of organic molecules (amino acids, vitamins, peptides and drugs) at the μITIES. Stripping analysis at micro-interface arrays is suitable for the detection of analytes in several real media including water, soil extracts and biological fluids (blood and saliva) with high specificity, sensitivity (detection limits of nM, ppb level) and reliability. Stripping analysis at μITIES and micro-electrode arrays are two complementary approaches that have the advantages of being cost effective, simple to use and easily adaptable to field measurement.     

Stripping voltammetry with collection at a rotating ring-disk electrode

A new electroanalytical technique is described, called "stripping voltammetry with collection." The technique involves the use of a rotating ring-disk electrode and is an improvement over traditional voltammetric stripping at a single electrode in that it is characterized by a lower limit of detection and that the period of deposition before stripping can be shorter. The use of the technique is illustrated by the determination of 10(-10)M Ag(+) in 0.1 M H(2)SO(4) by use of a ring-disk electrode having a disk electrode constructed of glassy carbon and a ring electrode constructed of platinum.     

Stripping voltammetry of silver ions at polythiophene-modified platinum electrodes

The present work describes the development of a modified platinum electrode for stripping voltammetric determination of silver. The deposition of films based on electropolymerisation of the monomer thiophene was carried out by cycling the potential towards positive values between 0 and 1.6 V.The preconcentration process of silver ions was initiated on the surface of the modified electrode by complexing silver with polythiophene (PTH) when a negative potential (−0.5 V) was applied; then the reduced products was oxidized by means of differential pulse stripping voltammetry and the peak was observed at 0.17 V. Parameters such as pH, supporting electrolyte and number of electropolymerisation cycles were studied. A linear relation between current peak and concentration of Ag(I) was obtained in the range 0.07-1.0 mg L⁻¹. The detection limit for Ag(I) was evaluated to be 0.06 mg L⁻¹. The reproducibility was tested carrying out 11 measurements at different electrodes and the relative standard deviation was 1.5%. The interference of several metals was investigated and showed negligible effect on the electrode response.     

Stripping voltammetry of trace metals in resistive solutions with mercury microelectrodes

Mercury-coated microcylindrical carbon-fiber electrodes (7-μm diameter) are suitable for anodic-stripping voltammetric quantitation of trace metals in non-aqueous solvents. The stripping voltammograms show no distortion resulting from uncompensated ohmic drops when traces of lead, cadmium, and zinc are quantified in acetonitrile, methanol or ethylene glycol. In contrast, analogous measurements at macro-sized electrodes exhibit severe ohmic effects. Organic solutions containing extremely dilute electrolyte (or no deliberately added electrolyte) can be assayed. A two-electrode configuration yields virtually undistorted stripping voltammograms in methanol and acetonitrile. High sensitivity and good precision are obtained by using quiescent solutions.     

Stripping voltammetry of bromide and iodide ions at a renewal silver electrode

The behavior of bromide and iodide ions at a silver electrode renewed by cutting off a thin 0.5-μm surface layer was studied. The advantage of this method of electrode renewal over some variants of mechanical renewal was demonstrated. It was shown that bromide and iodide ions can be determined in concentration ranges from 10^-6 to 10^-3 M and from 10^-7 to 10^-3 M, respectively. Deceased.     

Stripping voltammetry of copper and lead using gold electrodes modified with self-assembled monolayers

One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes. Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes. The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed. Received: 29 May 1997 / Accepted: 24 June 1997     

Determination of Titanium In Quartz and Silica Glass Samples By Adsorptive Stripping voltammetry

ABSTRACT

This article presents a method for determination of titanium in quartz and silica glass samples based on adsorptive stripping voltammetry (AdSV) with mandelic acid. Hanging mercury drop electrode as a working electrode was used. The optimized conditions include: pH 3.3, accumulation potential –0.15 V, accumulation time 90 s, scan rate 10 mV/s, pulse amplitude 25 mV. In case of 5 min accumulation time the obtained detection limit was 6.5×10^-9 mol/L Ti. ET-AAS was applied as a reference method to AdSV measurements. The procedure for decomposition of quartz and silica glass samples applying small amount of acids is described.     

Stripping voltammetry of carbon monoxide oxidation on stepped platinum single-crystal electrodes in alkaline solution

The electrochemical oxidation of a CO adlayer on Pt[n(111)x(111)] electrodes, with n = 30, 10, and 5, Pt(111), Pt(110) as well as a Pt(553) electrode (with steps of (100) orientation) in alkaline solution (0.1 M NaOH) has been studied using stripping voltammetry. On these electrodes, it is possible to distinguish CO oxidation at four different active oxidation sites on the surface, i.e. sites with (111), (110) and (100) orientation, and kink sites. The least active site for CO oxidation is the (111) terrace site. Steps sites are more active than the (111) terrace sites, the (110) site oxidizing CO at lower potential than the (100) site. The CO oxidation feature with the lowest overpotential (oxidation potential as low as 0.35 V vs. RHE) was ascribed to oxidation of CO at kink sites. The amount of CO oxidized at the active step or kink sites vs. the amount of CO oxidized at the (111) terrace sites depends on the concentration of the active sites and the time given for the terrace-bound CO to reach the active site. By performing CO stripping on the stepped surfaces at different scan rates, the role of CO surface diffusion is probed. The possible role of electronic effects in explaining the unusual activity and dynamics of CO adlayer oxidation in alkaline solution is discussed.     

Multielement analysis in stripping voltammetry

An original software that allows different versions of stripping voltammetry to be used in domestic Khan-2 and VA-03 computer-controlled analyzers is tested. An increase in the number of metal ions to be determined in a sample by stripping voltammetry to five or more components is exemplified by the determination of the components of the Cd(II)-Pb(II)-Cu(II) model system in the proposed supporting electrolyte (NH₄Cl, pH 2–4) at a gradiently formed mercury-graphite electrode. These conditions provide the stability of a droplet mercury coating of the electrode, a change in the potentials of the group deposition of the components, and the optimization of the analytical signals. The analytical potential of the specified approaches are estimated by determining the number of components in the control and real-water samples using different methods.     

Recent applications of thermal lens spectrometry in food analysis and environmental research

This review summarizes the most recent achievements related to the application of thermal lens spectrometry (TLS) in food analysis and environmental research. All the applications are associated with the use of an appropriate analytical procedure providing sufficient selectivity, that cannot be achieved by TLS itself. Several selective reagents, biosensors and chromatographic separation procedures (IC, HPLC), used for this purpose, and their performance in combination with TLS, are described. Heavy metals and related species, pesticides, carotenoids, fatty acids, and their determination in samples such as water, fruit juices, oils and marine phytoplankton were given most consideration. The main advantages of novel analytical methods include improved sensitivity and selectivity, simplicity, minimized need for sample preparation and handling as well as reduced time of analysis.     

Biosensors based on screen-printing technology,and their applications in environmental and food analysis

This review summarizes scientific research activity on biosensors, especially screen-printed, electrode-based biosensors. The basic configurations of biosensors based on screen-printing technology are discussed and different procedures for immobilization of the biorecognition component are reviewed. Theoretical aspects are exemplified by practical environmental and food-analysis applications of screen-printed, electrode-based biosensors.