Anodic stripping voltammetry with medium exchange in trace element speciation

The application of medium exchange in anodic stripping voltammetry (ASV) was investigated by determing the fractions of ASV-labile copper, lead, cadmium and zinc in the presence of a variety of natural and sysnthetic ligands in a soft water. Pristin and polluted samples of river water were also tested. Medium exchange, where the test solution is replaced after electrodeposition by a simple electrolyte such as acetate buffer, before the oxidation (stripping) of the deposited metals, can ensure that the ASV-labile metal fraction depends only on the parameters of the electrodeposition step. Significant differences were found for ASV-labile fractons when medium exchange was used for the two river water samples, and for several mertal/ligand combinations such as copper/chloride, copper/humic acid, and zinc/tannic aid. It is recommended that medium exchange be used routinely for ASV-labile determinations.     

Copper Complexation with Soluble and Surface Freshwaters Ligands

Speciation of copper has been done using samples collected at different times of the year (December 92 and October 93) and in three sites of a polluted river (Este River, Northern Portugal). Filtered samples and the suspended particulate matter were titrated with metal ion and the labile metal concentrations measured by anodic stripping voltammetry (DPASV). An extra peak in the Cu voltammograms has been noticed when titrating filtered samples and its origin was investigated. Results have suggested that the extra peak is due to copper(I) stabilized by ligands adsorbed on the mercury electrode and a model for the electrochemical mechanism is proposed. From titrations of the same samples with zinc, cadmium and lead it has been concluded that there are two types of organics in the river water: macromolecules and small molecules with D_ML≈D_M with higher affinity for soft cations such as Cd(II) and Cu(I), that can be adsorbed on mercury electrode as anions.     

Development of physico-chemical speciation procedures to investigate the toxicity of copper,lead, cadmium and zinc towards aquatic biota

A range of model compounds was studied to test the effect of complexing agents on the adsorption of copper, lead, cadmium and zinc by Chelex-100 resin, oxine porous glass, thiol porous glass and thiol resin, from seawater and distilled water. The thiol materials, while showing behaviour similar to Chelex-100 resin and oxine porous glass for zinc, cadmium and lead, retained copper much more strongly. Methods for measuring lipid-soluble metal complexes in waters were also studied. Bio-Rad SM2 resin was the most suitable extractant, although a citrate buffer of pH 5.7 was needed to prevent the co-adsorption of free metal ions. Seawater and various fresh waters were analyzed for trace metal speciation by using Chelex-100 resin, thiol resin and anodic stripping voltammetry to determine labile metal. Bio-Rad SM2 resin and hexane—butanol extraction were used for the estimation of lipid-soluble metal. The polluted water samples had higher fractions of labile and organic-soluble metal, but it was concluded that some of the waters contained unidentified ligands which caused speciation behaviour different from that of the synthetic solutions with model ligands. The factors involved in the choice of speciation procedures for the measurement of the toxic fraction of a metal in a water sample are discussed in detail.     

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper,lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.     

The use of Nafion-coated thin mercury film electrodes for the determination of the dissolved copper speciation in estuarine water

Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L₁-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu²⁺] in the San Francisco Bay estuary.     

Increased sensitivity of anodic stripping voltammetry at the hanging mercury drop electrode by ultracathodic deposition

An improved approach to the anodic stripping voltammetric (ASV) determination of heavy metals, using the hanging mercury drop electrode (HMDE), is reported. It was discovered that using very cathodic accumulation potentials, at which the solvent reduction occurs (overpotential deposition), the voltammetric signals of zinc(II), cadmium(II), lead(II) and copper(II) increase. When compared with the classical methodology a 5 to 10-fold signal increase is obtained. This effect is likely due to both mercury drop oscillation at such cathodic potentials and added local convection at the mercury drop surface caused by the evolution of hydrogen bubbles.     

Continuous sonoassisted digestion coupled to flow injection minicolumn separation for the determination of total and labile Cu and Fe in fresh waters by flame atomic absorption spectrometry

An automatic on-line system is developed for the trace determination of copper and iron species in fresh waters by flame atomic absorption spectrometry using only 5 and 2?mL of sample, for copper and iron determination, respectively. This system, which includes a home-made minicolumn of commercially available resin containing aminomethylphosphonic acid functional groups (Chelite P), comprises two operational modes. The first, used for the determination of the dissolved labile fraction (free copper and iron ions and their weak complexes) is based on the elution of this fraction from a minicolumn containing the chelating resin loaded in-situ with the sample. The second mode is used for the determination of total trace copper and iron concentrations. This last mode is based on the retention/preconcentration of total metals on the Chelite P resin after on-line sonoassisted digestion of water samples acidified with nitric acid (0.5?mol?L^?1 final concentration) to break down metal organic complexes present in fresh waters as river waters. The figures of merit for copper and iron determination in both fractions are given and the obtained values are discussed. The analytical method was characterized and the limit of detection and limit of quantification for the two metals were 0.5 and 1.6?µg?L^?1 for Cu and 2.3 and 6.1?µg?L^?1 for Fe, respectively. The repeatability, expressed as relative standard deviation, was in the range 1.0–2.1%. The speciation scheme was applied to the analysis of river surface water samples collected in Galicia (Northwest, Spain).     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Determination of Copper,Cadmium, Zinc And Lead In ArgeŞ River In Romania During Four Seasons By Inductively Coupled Plasma Atomic Emission Spectrometry And Anodic Stripping Voltammetry

ABSTRACT

The paper represents a continued study of selected heavy metals concentration in the Arge? River, the fifth river in length from Romania.

For the determination of metal ion concentration in Arge? river was used Atomic Absorption Spectrometry for sodium, potassium and magnesium; Direct Coupled Plasma Atomic Emission Spectrometry for calcium; Inductively Coupled Plasma Atomic Emission Spectrometry for copper, cadmium, zinc, aluminium, lead, titanium, zirconium, chromium, molybdenum, manganese, iron and nickel.

Copper, cadmium, zinc and lead concentration were determined by ICP–AES and ASV and results were reliable.

By comparison of the results a good agreement between these two techniques is observed.     

A new procedure for the speciation of mercury in water based on the transformation of mercury (II) and methylmercury (II) into stable acetylides followed by HPLC analysis

Conversion of mercury(II) and methylmercury(II) species dissolved in water into di(phenylethynyl)mercury and methyl(phenylethynyl) mercury takes place in satisfactory yield under alkaline conditions by stirring the aqueous solution with phenylacetylene at room temperature. Mercury speciation is simply obtained by HPLC analysis of the two organometallic species. The presence of heavy metals such as copper(II), zinc(II), cadmium(II) and lead(II) in concentrations 10000 times higher than mercury is tolerated, while little interference is displayed by humic acids and cysteine. Seawater samples can also be analysed following a properly adapted procedure.     

Application of a Carbon Paste Electrode Modified with a Schiff Base Ligand to Mercury Speciation in Water

A carbon paste electrode, modified with benzylbisthiosemicarbazone is used for mercury speciation in water samples. Mercury ion is selectively accumulated on the electrode surface at open circuit and its analysis was performed by cyclic voltammetry or square‐wave voltammetry (SWV). A detection limit of 8 μg L^?1 (3σ) was found for 15 min of accumulation using SWV as measurement technique. The effect of several metallic ions and organic substances on voltammetric signal is examined. For speciation purposes, a ligand competition methodology between ligands in solution and electrode is used. Model mercury complexes are characterized as a function of their dissociation kinetics. The method was applied to mercury speciation in water samples from the Jarama River in Madrid.     

Simultaneous and Selective Detection of Environment Hazardous Metals in Water Samples by Using Flower and Christmas Tree Like Cerium Hexacyanoferrate Modified Electrodes

We report facile, template‐free, surfactant‐less flower and Christmas tree‐like cerium hexacyanoferrate (CeHCF) modified electrodes for simultaneous measurement of environmentally hazardous metals. The hierarchical growth of CeHCF on electrode surface was controlled by electrodeposition time at constant potential. This CeHCF modified electrode exhibits a prominent electrocatalytic activity towards detection of heavy metal ions such as cadmium (Cd), copper (Cu), lead (Pb) and mercury (Hg). The peaks are separated well at CeHCF modified electrode. Well separated peaks for the detection of these heavy metals in lake and tap water samples indicating CeHCF modified electrode as successful electrode for the reported sensor.     

Synthesis and properties of a chelating resin containing triazolethiol groups

A macroreticular poly(acrylic acid)-based resin with triazolethiol as the functional group has been synthesized. The stability of the resin in acidic media and the behaviour in sorption and desorption of various metal ions have been investigated and compared with those of the acylthiosemicarbazide resin which is an intermediate in synthesis of the triazolethiol resin. Both resins show high affinity for copper(II) silver, cadmium and mercury(II), and high selectivity for silver and mercury(II) at low pH (1–2), and even at pH 7 if EDTA is present. The triazolethiol resin sorbs metal ions faster than the acylthiosemicarbazide resin does and sorbs mercury(II) from high concentrations of acids and neutral salt solutions. This resin has been applied to the concentration of silver and mercury(II) from sea-water samples by column operation.     

A novel adsorbent for the determination of the toxic fraction of copper in natural waters

A novel adsorbent for the determination of the toxic fraction of copper in natural waters is described. Aluminium hydroxide adsorbed on a sulfonic acid cation-exchange resin quantitatively retains copper(II) ions in the absence of organic ligands such as fulvic, humic and tannic acids. In the presence of these ligands, a smaller fraction of copper is adsorbed and can be related to the toxic fraction. The toxic fraction determined by this method agreed well with results of algal assay with the marine diatom Nitzschia closterium in seawater and the green alga Chlorella pyrenoidosa in a synthetic soft water. The aluminium hydroxide-coated column also quantitatively adsorbs lipid-soluble copper complexes, which can be leached selectively from the column with methanol. The Al:OH ratio on the resin was 1:2 and the conditional stability constants (log K) of the Cu²⁺-adsorbent complexes in seawater and synthetic soft water were found to be 9.87 and 11.10, respectively; these values are similar to the equilibrium constatns for the reaction between Cu²⁺ and algae. The application of this adsorbent in an in-situ instrument for the continuous, unattended determination of the toxic fraction of copper and some other toxic metals in natural waters is outlined.     

Characterization of anthropogenic sediment particles after a transboundary water pollution of river Tisza using synchrotron radiation

At the beginning of 2000, a major mining accident occurred in the Romanian part of the Tisza catchment area due to tailings dam failure releasing huge amounts of heavy metals to the river. Sediment samples were taken from the main riverbed at six sites in Hungary, on March 16, 2000. The objective of this work was to characterize the anthropogenic particles in river sediment previously selected by single-particle electron probe X-ray microanalysis (EPMA). The trace element composition, heterogeneity and heavy metal speciation of individual particles was studied using synchrotron radiation-based microbeam X-ray emission and absorption methods. Particles were selected only from samples regarded as polluted sediment. White-beam micro X-ray fluorescence (μ-XRF) allowed the quantitative determination of heavy metals such as cadmium in individual particles. The maximum observed concentration of cadmium (>700 μg/g) indicates that this highly toxic heavy metal is concentrated in individual anthropogenic particles. Using the combination of micro X-ray absorption near-edge structure and target-transformation principle component analysis, quantitative chemical speciation of copper and zinc was feasible on individual sediment particles. Heavy metals in most of the particles released from the pollution site remained in the sulfide form resulting in a limited mobility of these metals. Based on the information obtained using microanalytical methods, the estimation of the environmental mobility of heavy metals connected to microparticles becomes possible.     

Heated mercury film electrode for anodic stripping voltammetry

A directly heated mercury film electrode (MFE) extends the operational capabilities of the hot layer technique to a wide range of electroanalytical systems. Wires or layers of gold and platinum have been used as sensors so far, but they were suitable only for the analysis of a small number of metals. The development of a heated MFE is described, including electrode construction and mercury deposition procedures. The thermal properties of the sensor were investigated. As a first application, cadmium was determined by anodic stripping voltammetry (ASV) with the result of an improved signal-to-background ratio.     

Determination of Cadmium(ii), Copper(ii), Mercury(ii), and Lead(ii) in Water Using Stochastic Sensors Based on Graphite and Diamond Paste Modified with 1H-Pyrrole-1-Hexanoic Acid

Graphite/diamond pastes modified with 1H-pyrrole-1-hexanoic acid were used for the design of stochastic sensors. The proposed stochastic sensors were used to determine four heavy metals, copper(II), cadmium(II), mercury(II), and lead(II), in water samples. The sensitivities of the stochastic sensors were high for all four metal ions, and their limits of determination were sufficiently low to enable detection at very minute concentrations; in some cases, unreachable using standard methods of analysis. The recoveries of copper(II), cadmium(II), mercury(II), and lead(II) in water samples were higher than 93.00%, with relative standard deviation values lower than 1.00%. The sensors were used to simultaneously determine copper(II), cadmium(II), mercury(II), and lead(II) in water samples. The obtained results were in agreement with those obtained using standard analytical methods.     

Literature survey of on-line elemental speciation in aqueous solutions

The literature about the on-line speciation in water has been comprehensively studied. Critical examination of this subject reveals that a great deal of work has been performed in this area for inorganic metal species and some organic compounds. The topic studied mainly includes the speciation of chromium, selenium, copper, arsenic, lead, cadmium, mercury, iron, aluminium, nickel, tin, antimony, phosphorus, nitrogen and others. The present literature survey includes also comments about the possibilities and problems of speciation as a function of analytical steps, general strategies involved and methods proposed in the literature for each element or a series of elements.     

Use of sodium dodecyl sulfate as an antifouling and homogenizing agent in the direct determination of heavy metals by anodic stripping voltammetry

The effectiveness of the anionic surfactant sodium dodecyl sulfate (SDS) for suppressing adsorption interferences in anodic stripping voltammetry (ASV) was investigated. The samples included fruit juices, wine, beer, milk powder and waste water, and the analytes were cadmium, lead and copper. In most of the samples, the ASV signals were severely depressed or even absent due to electrode fouling, but addition of SDS in concentrations up to 10 g L(-1) proved effective in restoring the ASV response. By using SDS as an interference suppressor, the content of lead and copper in a milk powder reference material was determined, and the results were in agreement with the certified values. In this determination, which could not have been performed without SDS, the surfactant also served as a homogenizing agent, preventing separation of the sample components. The effect of SDS was explained by the interaction of the surfactant with the electrode surface and with the constituents of the sample matrix.     

On-line collection/concentration and determination of transition and rare-earth metals in water samples using Multi-Auto-Pret system coupled with inductively coupled plasma-atomic emission spectrometry

On-line preconcentration and determination of transition and rare-earth metals in water samples was performed using a Multi-Auto-Pret system coupled with inductively coupled plasma-atomic emission spectrometry (ICP-AES). The Multi-Auto-Pret AES system proposed here consists of three Auto-Pret systems with mini-columns that can be used for the preconcentration of trace metals sequentially or simultaneously, and can reduce analysis time to one-third and running cost of argon gas and labor. A newly synthesized chelating resin, ethylenediamine-N,N,N′-triacetate-type chitosan (EDTriA-type chitosan), was employed in the Multi-Auto-Pret system for the collection of trace metals prior to their measurement by ICP-AES. The proposed resin showed very good adsorption ability for transition and rare-earth metal ions without any interference from alkali and alkaline-earth metal ions in an acidic media. For the best result, pH 5 was adopted for the collection of metal ions. Only 5 mL of samples could be used for the determination of transition metals, while 20 mL of samples was necessary for the determination of rare-earth metals. Metal ions adsorbed on the resin were eluted using 1.5 M nitric acid, and were measured by ICP-AES. The proposed method was evaluated by the analysis of SLRS-4 river water reference materials for trace metals. Good agreement with certified and reference values was obtained for most of the metals examined; it indicates that the proposed method using the newly synthesized resin could be favorably used for the determination of transition and rare-earth metals in water samples by ICP-AES.