The determination of zinc,cadmium, lead and copper in a single sea-water sample by differential pulse anodic stripping voltammetry

A comparative study is described of the anodic stripping voltammetry of sea water at its natural pH and at acetate-buffered pH, with a mercury film electrode. The reproducibility of the oxidation current peaks for copper and lead is improved and the electrode memory effect decreases, when the sample is acetate-buffered (pH 5.8). Determinations of zinc at the natural pH of sea water are inaccurate, because of the formation of Zn—Cu and Zn—Ni intermetallic compounds in the mercury film. The formation of such compounds can be prevented by the addition of gallium ions to acetate-buffered samples. A procedure for the determination of Cu, Pb, Cd and Zn in sea water is described.     

Measurements of trace concentrations of mercury in sea water by stripping chronopotentiometry with gold disk electrode: influence of copper

A stripping chronopotentiometric method, using a rotating gold disk electrode for mercury measurements in sea water is described. Compared with a same method using a stationary gold film electrode, this method has a eight times higher sensitivity and a detection limit of 5 ng l⁻¹ after 10 min deposition time. Moreover, the time needed for gold plating is eliminated. Compared with other electrochemical methods capable of measuring mercury at low concentrations, the present method is more simplified with no degassing step and no need to use a medium-exchange procedure before the stripping step. These characteristics render the method easily practicable on board oceanographic vessels for ‘in situ’ measurements.     

In situ electrodeposition for the determination of lead and cadmium in sea water

Electrodeposition techniques for the direct determination of lead and cadmium in sea water at the natural pH and in the presence of dissolved oxygen are examined. Anodic stripping voltammetry, at either the hanging mercury drop electrode or glassy carbon thin film electrode, is suitable for the determination of labile lead and cadmium. The presence of dissolved oxygen increases the height of the lead wave with a shift to more negative potentials. A more versatile technique is in situ deposition of labile metals on a mercury-coated graphite tube electrode. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals are determined by electrothermal atomic absorption spectrometry.     

The differential pulse anodic stripping voltammetry of copper and lead and their determination in EDTA extracts of soils with the mercury film glassy carbon electrode

The differential pulse anodic stripping voltammetry of copper and lead at the mercury film glassy carbon electrode is discussed. The mercury film prevents the occurrence of a monolayer stripping peak for copper. The influence of antimony and bismuth on the anodic stripping voltammetric behaviour of copper and lead is discussed. An interaction between copper and antimony distorts the copper stripping peak and gives rise to an intermediate peak. The method described is suitable for determining copper and lead simultaneously in EDTA extracts of soils.     

Staircase voltammetry as a rapid detection method for anodic stripping determination of lead

Rapid-scan staircase voltammetry is used to strip lead plated on a rotating mercury film electrode. With potential steps of 10 mV every 64 μs, the entire stripping of the metals is made in only 4 ms. Noise is reduced by averaging several current measurements on each step. The method allows quantification of 0.1 μg l^?1 lead within a total time to less than 4 min. Because of the rapid scan, the rotation of the electrode can continue during the stripping step. Oxygen does not affect the measurements although a small decrease in current is observed. The method is tested on a sample of sea water. Some results are also given for cadmium.     

Comparison of physicochemical speciation procedures with metal toxicity to chlorella pyrenoidosa

Metal speciation as measured by anodic stripping voltammetry (ASV), adsorption on a resin with adsorbed hydrated aluminium oxide, and dialysis with receiving resins is compared with the toxicity of the metals to the freshwater green alga Chlorella pyrenoidosa Chick. In the presence of natural and synthetic ligands, similar labile fractions of metals were obtained for ASV at three electrodes (hanging mercury drop electrode, mercury film electrode and Nafion-coated mercury film electrode). The toxic fractions determined by ASV and bioassay were in reasonable agreement for zinc, cadmium and copper, and alteration of the analytical conditions provided some measure of agreement for lead. The resin with adsorbed hydrated aluminium oxide correlated well with bioassay for copper, but over-estimated lead toxicity and under-estimated cadmium toxicity. Dialysis with receiving resins under-estimated metal bioaccumulation in the presence of ligands. Metal speciation analysis for water samples gave higher toxic fractions for metals in samples of polluted river water and road runoff samples than those found in pristine river water.     

Electrodeposition of mercury film on electrodes modified with clay minerals

A new type of carbon paste electrode modified with clay mineral and covered with a mercury film is presented in this work. Electrodeposition of the mercury film was performed on the carbon paste electrode modified with montmorillonite. The mercury film was deposited by both electrodeposition in situ and a preliminary electrodeposition. The pre-deposited film of mercury showed to be suitable for anodic stripping voltammetry. An open-circuit sorption of Cd, Pb, and Cu with subsequent anodic stripping voltammetry exhibited higher current responses of metals. Besides the enhanced sensitivity superior separation of the current responses during a simultaneous stripping of metals is expected to be achieved by means of the newly prepared electrode. Presented at the 57th Congress of Chemical Societies, Tatranské Matliare, 4–8 September 2005.     

The determination of copper,lead and cadmium in sea water by differential pulse anodic stripping voltammetry

The effect of various instrumental parameters is investigated and optimized conditions established. The results are in accordance with the theory of differential pulse anodic stripping voltammetry. Both a hanging mercury drop electrode, and a rotating glassy carbon electrode mercury plated in situ were used. The best detection limit is obtained with the mercury film electrode, but the hanging mercury drop electrode is more reproducible. The differential pulse stripping technique is compared to linear sweep stripping, and increased sensitivity and better peak separation is demonstrated for the former technique, particularly when a hanging mercury drop electrode is used. However, the differential pulse technique will also improve the detection limit for a mercury film electrode, if the electrode has a non-ideal response with a corresponding high background current.     

Voltammétrie de l'argent par redissolution anodique sur electrode de carbone vitreux et application au dosage de l'argent dans l'uranium et le pluton

Anodic stripping voltammetry of silver on a glassy carbon electrode, and application to the determination of silver in uranium and plutonium.The use of a glassy carbon electrode for the anodic stripping voltammetry of silver, without deposition of a preliminary mercury film is described. The deposition time, scan rate, rotation speed and molarity of the sulfuric solution have been studied; the method is applied to the determination of silver in uranium and plutonium.     

Graphite multi-micro-disc based mercury film electrode: Comparison of experimental and theoretical anodic stripping results

an ensemble of properly distanced micro mercury film electrodes (MMFE) was used in cyclic and anodic stripping voltammetry. the experimental results were compared with the anodic stripping theory, and the agreement was found to be satisfactory. The MMFE peaks (calculated per unit area) were higher, thinner and shifted towards more negative potentials compared with the large area mercury film electrode (LAMFE) peaks.The initial graphite electrode consisted of 65 independent micro-discs forming a circle, and was prepared from carbon fibres 4.66 μm in radius. The graphite multi-micro-disc electrode was quantitatively checked in a Fe(CN)₆^3? solution under both chronoamperometric and voltammetric conditions. The deposition and oxidation of mercury is discussed also.     

Derivative potentiometric stripping analysis with a thin film of mercury on a glassy carbon electrode

Derivative potentiometric stripping analysis is based on the pre-concentration of metal analytes in a thin film of mercury on a glassy carbon electrode and subsequent measurement of the electrode potential subject to controlled transport of oxidant to the electrode surface. The mechanism for the stripping process with respect to oxidant concentration, electrode rotation rate and instrument parameters is discussed, together with analytical results and applications.     

Determination of traces of metals by anodic stripping voltammetry at a rotating glassy carbon ring—disc electrode: Part 1. Method and instrumentation with evaluation of some parameters

The equipment and procedure are described for the determination without preconcentration of several heavy metals based on d.c. anodic stripping voltammetry at a rotating ring—disc glassy carbon electrode with in situ mercury plating. During stripping of the metals deposited on the disc, the current from the reduction of the ions collected at the ring is measured. Some parameters (scan rate, thickness of the mercury film, electrode rotation and deposition time) influencing the ring collection peak current are examined experimentally. The results are compared with the theoretical considerations given by de Vries and van Dalen for anodic stripping voltammetry on a stationary mercury film electrode and by Bakanov et al. for a rotating mercury film electrode.     

Anodic stripping voltammetry in a flow-through cell with a fixed mercury film glassy carbon disc electrode. Part I

Anodic stripping voltammetry at a glassy carbon disc electrode covered by a thin mercury film was adapted for use in a flow-through cell. The resulting system is characterized by extreme simplicity of set-up and operation, high sensitivity and excellent precision and stability. Its performance was tested via the determination of hydrated or labile complex ions of heavy metal ions in sea water, using short (2–10 min) deposition periods. The dependence of the stripping peak charge on metal ion concentration, length of deposition period, solution flow rate and other variables was examined and the reliability of the results obtained were evaluated under conditions resembling continuous monitoring.     

The determination of platinum in sea water by adsorptive cathodic stripping voltammetry

The catalytic effect of the formazone complex with platinum on the development of hydrogen at a mercury electrode is used to provide a very sensitive method of determining dissolved platinum in fresh and sea water by adsorptive cathodic stripping voltammetry. The optimal analytical conditions include the addition of 0.012% (w/v) formaldehyde, 0.0015% (w/v) hydrazine and 0.5 M sulphuric acid to the sea water. The complex is adsorbed for 1–20 min at ?0.925 V on the hanging mercury drop electrode, followed by a differential-pulse scan in a negative direction. The hydrogen reduction peak catalysed by the platinum complex appears at ?1.045 V. The limit of detection is 0.04 pM Pt with an adsorption time of 10 min, which is quite sufficient to determine dissolved platinum in sea water. The interference of surface-active compounds is eliminated by ultraviolet irradiation of the acidified sample. The method is applied to several sea-water samples. Comparative experiments showed that stripping chronopotentiometry is not sufficiently sensitive to determine platinum in sea water without preconcentration.     

Poly(ester sulphonic acid) coated mercury thin film electrodes: characterization and application in batch injection analysis stripping voltammetry of heavy metal ions

Mercury-thin film electrodes coated with a thin film of poly(ester sulphonic acid) (PESA) have been investigated for application in the analysis of trace heavy metals by square wave anodic stripping voltammetry using the batch injection analysis (BIA) technique. Different polymer dispersion concentrations in water/acetone mixed solvent are investigated and are characterised by electrochemical impedance measurements on glassy carbon and on mercury film electrodes. The influence of electrolyte anion, acetate or nitrate, on polymer film properties is demonstrated, acetate buffer being shown to be preferable for stripping voltammetry applications. Although stripping currents are between 30 and 70% less at the coated than at bare mercury thin film electrodes, the influence of model surfactants on stripping response is shown to be very small. The effect of the composition of the modifier film dispersion on calibration plots is shown; however, detection limits of around 5 nM are found for all modified electrodes tested. This coated electrode is an alternative to Nafion-coated mercury thin film electrodes for the analysis of trace metals in complex matrices, particularly useful when there is a high concentration of non-ionic detergents.     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.     

水中痕量汞的半微分阳极溶出分析

本文提出了测定痕量汞的半微分阳极溶出伏安法。玻碳电极用2,2’-联吡啶乙醇溶液进行修饰后再电镀—层金膜。支持电解质为0.1mol/HCl,修饰电极的重现性和灵敏度优于未修饰电极。讨论了予电解电位、予电解时间、电极转速和支持电解质的影响。溶出峰高与汞浓度在0.2～60ng/ml范围内呈良好线性关系,检测下限为0.11ng/ml。本法已用于自来水、雨水和深井水中汞的测定,获得满意结果。     

Atomic-absorption spectrometric determination of cadmium,lead and zinc in salts or salt solutions by hanging mercury drop electrodeposition and atomization in a graphite furnace

Atomic absorption spectrometric methods are described for the determination of trace amounts of cadmium, lead and zinc in salts or salt solutions. The metals are separated from the salt matrix by electrolysis on a hanging mercury drop electrode, the mercury is transferred to a graphite boat and removed by evaporation, and the metals are determined by atomization. The feasibility of the technique was tested by analysis of sea water and of reagent-grade potassium chloride. For comparison the three metals were also determined in the sea water by stripping voltammetry, good agreement being found.     

Influence of hydrodynamic conditions of the solution on the sensitivity of stripping analysis of trace metals

Possibilities to increase the sensitivity of stripping analysis by optimising the hydrodynamic conditions of the solution during the deposition and rest period are evaluated. Rotation rates as high as 13 000 rpm can be applied during the deposition step at a mercury film rotating disc electrode for Zn, Cd, Pb, In and Tl determinations when 10–20 mg/l of Hg²⁺ for the renewal of the mercury film is added. Because of the extreme sensitivity on the properties of the mercury film in the case of Ga only 4000–5000 rpm are recommended. The highest stirring efficiencies using a magnetic stirrer are equivalent to 2500–3000 rpm when a rotating disc electrode is used. The effect of the duration of the rest period is not significant for square wave stripping voltammetry, however, analytical signals can be increased 10 and more times when potentiometric stripping analysis is applied.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.