Anodic Stripping Voltammetry of Heavy Metals at Nanocrystalline Boron‐Doped Diamond Electrode

Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD.     

Interactions of Pb(II) with particles of a polluted river

Pb(II) interactions with the surface of suspended matter from a polluted river was studied using differential pulse anodic stripping voltammetry (DPASV) technique. Three sampling sites were selected and studies have been done with samples collected in different times of the year (winter, autumn and summer). The values have been compared with those obtained in spring in the same conditions [Sci. Total Environ. 151 (1994) 101].Particles were separated by centrifugation and suspensions of the freeze-dried particles were titrated with Pb(II), being measured the labile metal fraction by DPASV. For comparison, suspensions of river water without any separation have also been titrated.Results show that surface metal complexes are inert, within the time scale of the analytical technique and desorbed organics from surfaces, form labile Pb(II) complexes in solution. For each sample it was determined the capacity for Pb complexation of particles and desorbed organics and the differential function has been estimated. Despite the heterogeneity of ligands, the systems interpreted in a discontinuous way, present one or two kinds of dominant ligands with Pb affinity.     

Recent Decrease in the Lead Concentration of Antarctic Snow

Abstract

Differential Pulse Anodic Stripping Voltammetry (DPASV) was applied to determine the lead concentration in recent snow at two sites in the Victoria Land region, East Antarctica. Snow samples were collected during the 6th Italian Scientific Expedition to Antarctica (austral Summer 1990–91) along the wall of 2.5 m-deep hand-dug pits and by coring to a depth of about 11 m. The measurements revealed that lead content in Antarctic snow increased continuously from 1965 (about 3 pg/g) to the early 1980s (maximum about 8 pg/g), after which a marked, rapid decrease took place during the second half of 1980s, down to 2–4 pg/g in 1991. Estimates of the lead contributions from rocks and soils, volcanoes and the marine environment, together with analysis of statistical data on non-ferrous metal production and gasoline consumption, and the corresponding lead emissions into the atmosphere of the Southern Hemisphere, show that a net anthropogenic component is present and support the hypothesis that the trend observed in Antarctic snow may be related to lead consumption in gasoline, which firstly was on the rise, then declined owing to the increased use of unleaded gasoline.     

Book reviews

Inorganic mercury ions (Hg²⁺) in laboratory prepared solutions were determined with a screen-printed carbon electrode (SPCE) coated with a polyaniline-methylene blue (PANI-MB) polymer layer. The structure and properties of the PANI-MB polymer layer were compared to that of normal polyaniline (PANI) in order to elucidate the structure of the PANI-MB layer. The electrically-conducting polymers were prepared by electrochemical polymerisation of monomer solutions of aniline, and mixed solutions of aniline with methylene blue onto respective screen-printed carbon electrodes (SPCEs). Scanning Electron Microscopy (SEM) analyses of the SPCE polymer coated electrodes have shown that nanostructured materials have formed with the diameters of the PANI nanoclusters and PANI-MB nanorods at approximately 200 nm. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of 1 × 10^?6 M Hg²⁺, in the presence of the SPCE/PANI-MB polymer sensor electrode. The Hg²⁺ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg²⁺ determination included the supporting electrolyte concentration and the accumulation time. The results obtained have shown that the SPCE/PANI-MB polymer sensor electrode operates optimally at a pH 2, with the supporting electrolyte concentration at 0.5 M HCl. A linear calibration curve was found to be in the range of 1 × 10^?8 M to 1 × 10^?5 M Hg²⁺ after 120 s of pre-concentration. The detection limit was calculated and found to be 54.27 ± 3.28 µg L^?1 of Hg²⁺. The results have also shown that a conducting polymer modified SPCE sensor electrode can be used as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg²⁺ ions.     

Dissolved Cu(II) Speciation in Unpolluted Soil Solutions of a Planosolic Horizon

Dissolved Cu(II) speciation in unpolluted soil solutions from different horizons was studied using differential pulse anodic stripping voltammetry (DPASV). Three sites were selected according to topography and monitored for three years. Experiments evidence Cu(II) can be bound by DOM (Dissolved Organic Matter) through complexation and/or adsorption reactions. The complexation capacity and the corresponding conditional stability constant were determined for complexation reactions. The adsorbing sites were titrated. A potential binding coefficient was calculated to compare both types of reactions. Results show adsorption is less frequent than complexation but exhibits higher binding coefficient.     

Development of an anodic stripping voltammetric assay, using a disposable mercury-free screen-printed carbon electrode, for the determination of zinc in human sweat

This paper reports on the development of a novel electrochemical assay for Zn²⁺ in human sweat, which involves the use of disposable screen-printed carbon electrodes (SPCEs). Initially, SPCEs were used in conjunction with cyclic voltammetry to study the redox characteristics of Zn²⁺ in a selection of supporting electrolytes. The best defined cathodic and anodic peaks were obtained with 0.1 M NaCl/0.1 M acetate buffer pH 6.0. The anodic peak was sharp and symmetrical which is typical for the oxidation of a thin metal film on the electrode surface. This behaviour was exploited in the development of a differential pulse anodic stripping voltammetric (DPASV) assay for zinc. It was shown that a deposition potential of −1.6 V versus Ag/AgCl and deposition time of 60 s with stirring (10 s equilibration) produced a well-defined stripping peak with E_pa = −1.2 V versus Ag/AgCl. Using these conditions, the calibration plot was linear over the range 1 × 10⁻⁸ to 5 × 10⁻⁶ M Zn²⁺. The precision was examined by carrying out six replicate measurements at a concentration of 2 × 10⁻⁶ M; the coefficient of variation was calculated to be 5.6%. The method was applied to the determination of the analyte in sweat from 10 human volunteers. The concentrations were between 0.39 and 1.56 μg/mL, which agrees well with previously reported values. This simple, low-cost sensitive assay should have application in biomedical studies and for stress and fatigue in sports studies.     

A sensitive determination of dopamine in the presence of ascorbic acid using a nafion-coated clinoptilolite-modified carbon paste electrode

A selective dopamine determination using a nafion-coated clinoptilolite-modified carbon paste electrode in the presence of ascorbic acid was studied. Both cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) were used for measurements of dopamine. To improve the selectivity of the clinoptilolite-modified carbon paste electrode in presence of a high concentration of ascorbic acid, the electrode surface was coated with nafion membrane. Experimental parameters affecting the determination of dopamine, including the clinoptilolite ratio, nafion membrane thickness, preconcentration time, preconcentration solution pH, stripping solution pH and interferences are discussed. The developed sensor has a wide linear range, a low detection limit, and good stability and reproducibility. The sensor offers a good alternative to existing analytical methods for dopamine, permits a relatively short analysis time, and is simple, selective and inexpensive.     

Interlaboratory study to improve the quality of trace element determinations in rainwater

This is the first publication which describes the development of a reference material (RM) for the determination of 11 trace elements (Cu, Pb, Mn, Ni, Zn, Fe, Cd, Co, V, As and Al) in rainwater at microgram per liter concentrations. An interlaboratory comparison study for the determination of trace elements in rainwater was carried out for material performance studies to establish analyte concentrations with a stated uncertainty. Fifteen reputed laboratories from Asia, Europe and North America participated in the study. These laboratories used their regular in-house methods to analyze the rainwater samples. The aim of this study is to establish concentration levels of trace elements in rainwater based on interlaboratory study results. Details of the production, homogeneity and stability of the reference sample are given in this article. The organization of the study and the quality assurance measures undertaken at the organizer's laboratory are described. The analytical results obtained from individual laboratories and the analytical methods used for the determination of trace elements in rainwater are discussed. Based on the results obtained from the intercomparison study, certified values as well as informative values are assigned to the 11 trace elements in rainwater.     

Determination of trace arsenic(III) by differential-pulse anodic stripping voltammetry with in-situ plated bismuth-film electrode

Abstract

A systematic survey of the quality status of the main aquifers in rural areas of Catalonia (Spain) regarding pesticide pollution has been carried out. A total number of 139 wells, distributed among 13 different hydrogeological units have been sampled and analyzed by GC-MS and GC-ECD, during the period 1997—98. Pesticides monitored were selected among triazine herbicides, organochlorine and organophosphorus insecticides. A positive presence of pesticides has been detected in 84.2% of the samples analyzed, 23.7% of them exceeding the requirements of the EU drinking water Directive (98/83/CE). Organochlorine insecticides were present in 62.6% of the samples, triazines in 49% and organophosphorus insecticides in 28.8%. The results obtained have been interpreted by Principal Component Analysis.     

Evaluation of cadmium–metallothionein stability constants based on voltammetric measurements

A voltammetric study on the binding properties of the commercially available rabbit liver metallothionein (MT) Sigma M 7641 for cadmium ions was performed. The capacity of metallothionein to complex cadmium and the stability constants of Cd–T complex (T denotes the apoprotein or thionein molecule) have been determined from the direct titration of the defined MT concentration with the standard CdCl₂ solution in 0.59 M sodium chloride medium at pH 7.9 and 2.0. At pH 7.9 the formation of the Cd–T complex has been followed measuring the specific anodic signal height of the complex. Stability constants of Cd–T have been evaluated from the experimental data using three different procedures. The calculated apparent stability constants K=(7.6±0.2)·10⁸ dm³ mol⁻¹ of Cd–T complex in 0.59 M NaCl at pH 7.9 and 25°C indicate that under the given experimental conditions all the three procedures are equally applicable.