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.     

H-point standard addition method in the analysis by differential pulse anodic stripping voltammetry Simultaneous determination of lead and tin

The applicability of H-point standard addition method (HPSAM) to the resolving of overlapping differential pulse anodic stripping voltammetric peaks corresponding to the oxidation of lead and tin is verified. The results show that the H-point standard addition method is suitable for the simultaneous determination of lead and tin in aqueous media. The results of applying the H-point standard addition method showed that Sn²⁺ and Pb²⁺ could be determined simultaneously with the concentration ratios of Sn²⁺ to Pb²⁺ varying from 1:5 to 10:1 in the mixed sample. The proposed method has been successfully applied to the simultaneous determination of lead in the presence of tin in some synthetic samples. Moreover, the applicability of the method was demonstrated by the recovery of lead in a canned soft drink sample.     

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

Differential pulse anodic stripping voltammetry is used for the simultaneous determination of cadmium, lead and copper in different types of urine samples. Unlike most biological samples, urine can be analyzed directly for cadmium and lead without pretreatment of the sample; a significant increase in sensitivity is obtained if the analysis is carried out at an elevated temperature. The complete decomposition of urine with a mixture of nitric, perchloric and sulphuric acids is also described; this procedure makes it possible to determine copper simultaneously. Good agreement was obtained between the two procedures, and the recovery of metals from spiked samples was satisfactory for both methods. The relative merits of the two approaches are discussed.     

The renovated silver ring electrode in determination of lead traces by differential pulse anodic stripping voltammetry

The study of a new type of working electrode - the renovated silver ring electrode (RSRE) - for lead ions detection via differential pulse anodic stripping voltammetry (DP ASV) without removal of oxygen is reported. The only four constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring, are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. Excellent repeatability and reproducibility - also in organic samples solutions - were reached in a period of a few weeks through the renovation of the electrode surface before each measurement. The reduction and stripping of lead on silver electrode under the DP ASV conditions are underpotential deposition/dissolution phenomena. The RSRE is used for the determination of Pb ions in concentrations ranging from 1 × 10⁻⁹ to 1 × 10⁻⁷ M. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 2%. Obtained calibration curves are represented by a correlation coefficient of at least 0.999. The detection limit (LOD) for the time of electrodeposition equal to 60 s is 0.2 × 10⁻⁹ M. LOD for Pb²⁺ detection at the RSRE is similar to this reported for a rotating silver electrode in subtractive anodic stripping voltammetry (E. Kirowa-Eisner, et al., Anal. Chim. Acta, 385 (1999) 325). The analysis of Pb²⁺ in synthetic solutions with and without surfactants, certified reference materials and natural water samples have been performed.     

A flow-through cell for differential pulse anodic stripping voltammetry

A flow-through voltammetric cell with a hanging mercury drop electrode has been developed to fit the static mercury drop electrode (PAR 303). The design has resulted in a linear increase of sensitivity with flow rate and an enhancement of sensitivity by the wall-jet effect. The cell is used in a flow injection system in which samples are introduced with a R??i?ka—Hansen injector. The mercury drop is held at plating potentials while the sample peak passes through the cell. Stripping is done under stopped flow conditions, to reduce noise, after the sample has been washed completely from the cell. The stripping thus takes place into the carrier electrolyte which always has a constant composition independent of sample constituents. Film-forming interfering species will, however, remain on the surface of the mercury drop. The effect of medium exchange on films produced by l-cysteine is reported. The flow-through medium exchange simplifies deaeration, speeds up analysis and reduces contamination.     

On-line coupling of sequential injection lab-on-valve to differential pulse anodic stripping voltammetry for determination of Pb in water samples

Sequential injection lab-on-valve (LOV) was first proposed for analyzing ultra-trace amounts of Pb using differential pulse anodic stripping voltammetry (DPASV) with a miniaturized electrochemical flow cell fabricated in the LOV unit. Deposition and stripping processes took place between the renewable mercury film carbon paste electrode and sample solution, the peak current was employed as the basis of quantification. The mercury film displayed a long-term stability and reproducibility for at least 50 cycles before next renewal, the properties of integrated miniature LOV unit not only enhanced the automation of the analysis procedure but also declined sample/reagent consumption. Potential factors that affect the present procedure were investigated in detail, i.e., deposition potential, deposition time, electrode renewable procedure and the volume of sample solution. The practical applicability of the present procedure was demonstrated by determination of Pb in environmental water samples.     

A modified method for the determination of lead in zircons by differential-pulse anodic stripping voltammetry

Zircons (20–100 mg) are decomposed within 1 h by fusion with potassium hydrogenfluoride followed by fuming with sulphuric acid. With differential-pulse anodic stripping voltammetry, after deposition for 1 min, the limit of detection for lead is 2 ng ml^?1 and the limit of quantitation is 6.6 ng ml^?1. Results (7–247 mg kg^?1 lead) are reported for nine zircons.     

Determination of antimony in impure zinc sulphate solution by coprecipitation followed by differential pulse anodic stripping voltammetry

A simple coprecipitation technique for the quantitative separation of the antimony present in impure zinc sulphate electrolyte followed by its voltammetric determination is described. Antimony in microgram levels is separated from the matrix zinc sulphate solution, which contains higher levels of copper, lead and cadmium, and is subsequently determined by differential pulse anodic stripping voltammetry (DPASV) in 3 M hydrochloric acid. Hydrous manganese dioxide is employed as the collector. This procedure, which effects considerable saving in time, is of comparable accuracy to the conventional spectrophotometric method using the antimony-rhodamine B complex. A series of synthetic zinc sulphate solutions spiked with known amounts of antimony as well as plant solutions gave near theoretical values.     

The determination of copper in silicon by anodic stripping and differential pulse voltammetry

A critical comparison of the application of differential pulse voltammetry and anodic stripping voltammetry to the determination of micro amounts of copper in silicon is described. The anodic stripping technique offers advantages when a dropping mercury capillary with a long drop time is used. The method recommended allows the determination of copper in silicon with a precision of ± 5 %; the limit of determination is about 1μg g^-1. Calibration graphs are linear in the range 0–0.2 μg Cu ml^-1. Methods for the dissolution of silicon are also compared.     

Determination of lead and cadmium in titanium dioxide by differential pulse anodic stripping voltammetry

A procedure for the simultaneous determination of lead and cadmium in TiO(2) by differential pulse anodic stripping voltammetry (ASV) has been developed. The key feature of the method is the use of triethanolamine (TEA) to remove titanium interference: TiO(2) undergoes acidic digestion with HF/H(2)SO(4) at atmospheric pressure, TEA is added to the HCl solution of the residue and the solution is analysed using a standard ASV instrumentation, equipped with a hanging mercury drop electrode. The calibration curves for both lead and cadmium are linear up to 50 mugl(-1) of solution, and the detection limits are 1 mugl(-1), corresponding to 1 mugg(-1) of TiO(2). Method reliability was tested by comparing the results with those given by electrothermal atomic absorption spectroscopy. The method has been successfully applied for determination of both contaminants in powdered titanium dioxide (raw materials) and in titanium dioxide-containing cosmetics (sunscreen products).     

Indirect trace determination of NTA in natural waters by differential pulse anodic stripping voltammetry

Summary Bismuth(III) is added to the water sample in excess to NTA and EDTA to form inert stable complexes with them at pH 2. The uncomplexed Bi(III) is then deposited into a hanging mercury drop electrode at a potential of –0.15 V vs. SCE and subsequently stripped anodically in the differential pulse mode. The peak current of uncomplexed Bi(III) is recorded. By a second deposition at –0.35 V vs. SCE Bi(III) from Bi³⁺ and Bi-NTA is deposited. The concentrations of NTA and EDTA in the sample are determined from the concentration of added Bi(III) and the voltammetrically determined Bi(III) at these two potentials by the standard addition method. Cd, Cu, Pb, and Zn do not interfere. Fe(III) has to be reduced by ascorbic acid or hydroxylamine before the determination. Cu(II) in concentrations larger than 40 g/l has to be removed by preelectrolysis. In samples with chloride contents above 0.05 M the stripping step has to be performed after medium exchange to a perchloric acid solution of pH 2. For a deposition time of 2 min the determination limit is approximately 0.2 g/l NTA and 0.1 g/l EDTA. The relative standard deviation for NTA concentrations at 2 or 10 g/l lies at 10 or 1.3%, respectively. Good accuracy is established by finding within 2% the levels adjusted when water samples are spiked with a standard solutions of NTA or EDTA.

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Indirekte Spurenbestimmung von NTA in natürlichen Wässern durch differentielle Pulsinversvoltammetrie

Zusammenfassung Bismuth(III) wird zur Wasserprobe in Überschuß zur NTA- und EDTA-Konzentration bei pH 2 zugegeben, wobei stabile inerte Komplexe gebildet werden. Nicht komplexiertes Bi(III) wird an der hängenden Quecksilbertropfenelektrode beim Potential –0,15 V (SKE) kathodisch als Amalgam abgeschieden und dann anodisch wieder gelöst. Dabei wird im differentiellen Pulsmodus der Bi(III)-peak registriert. Durch die zweite kathodische Abscheidung beim Potential –0,35 V (SKE) wird Bi(III) aus unkomplexiertem Bi³⁺ und dem BiNTA-Komplex abgeschieden. Die Konzentrationen von NTA und EDTA in der Probe werden aus den voltammetrisch bestimmten Bi(III)-Konzentrationen bei den zwei angegebenen Potentialen und der zugegebenen Konzentration von Bi(III) mit der Standard-Additions-Methode bestimmt. Die Spurenmetalle Cd, Cu, Pb und Zn stören die Bestimmung nicht. Fe(III) muß vor der Bestimmung mit Ascorbinsäure reduziert werden, Cu in der Konzentration von mehr als 40 g/l muß durch Vorelektrolyse entfernt werden. Wenn die Probe mehr als 0.05 M Chlorid enthält, muß der Strippingvorgang nach Elektrolytwechsel in einer Perchlorsäurelösung bei pH 2 durchgeführt werden. Für eine Anreicherungszeit von 2 min liegt die Bestimmungsgrenze bei 0,2 g/l NTA und 0,1 g/l EDTA. Die relative Standardabweichung beträgt bei einer Konzentration von 2, bzw. 10 g/l NTA 10 bzw. 1,3%. Die Richtigkeit ist gut, was aus der Wiederfindungsrate von 2% der zur Probe zugegebenen Lösung des NTA- oder EDTA-Standards hervorgeht.

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday

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On leave from the University of Thessaloniki, Greece     

Determination of gallium traces by differential pulse anodic stripping voltammetry

Summary The determination of gallium traces is carried out on the hanging drop mercury electrode in solutions of low ionic strength and in absence of complexing agents. At pH=3.2, where stable solutions are obtained, concentrations of 0.2 g Ga l^–1 are determinated with a standard deviation of 0.96% and a detection limit of 4 ng Ga l^–1.The effect of various instrumental parameters is investigated and optimized conditions established. The theory of differential pulse anodic stripping voltammetry is verified with the results obtained experimentally. The use of salicylate as base electrolyte is also considered.

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Bestimmung von Galliumspuren durch Differentialpuls-Anodic Stripping-Voltammetrie

     

Determination of cadmium, lead and copper in wine by differential pulse anodic stripping voltammetry

Summary The simultaneous determination of cadmium, lead and copper in wine by differential pulse anodic stripping voltammetry at the hanging mercury drop electrode is described. The wine samples are decomposed in a mixture of sulphuric acid and hydrogen peroxide at 180° C. The procedure is controlled by recovery tests and compared with other wet digestion methods. The results for ten red and white wine samples of different origin are given. The lead values (65–230 ppb) were below the accepted maximum level for this metal, but some of the wines contained relatively large amounts of copper (0.08–1.04 ppm). Very low values (1.4–6.6 ppb) were found for cadmium.

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Bestimmung von Cadmium, Blei und Kupfer in Wein durch Differentialpulse-anodic-stripping Voltammetrie

Zusammenfassung Bei dem beschriebenen Verfahren werden die Proben mit Schwefelsäure/Wasserstoffperoxid bei 180° C aufgeschlossen. Recovery Tests und Vergleiche mit anderen Naßaufschluß-methoden wurden durchgeführt. Ergebnisse für 10 Proben von Rot- und Weißweinen verschiedenen Ursprungs werden angegeben. Die Bleigehalte (65–230 ppb) lagen unter den zugelassenen Maximalwerten. Einige Weine wiesen jedoch relativ hohe Kupfergehalte auf (0,08–1,04 ppm). Cadmium wurde nur in sehr geringen Mengen gefunden (1,4–6,6 ppb).

We would like to thank A/S Vinmonopolet for supplying the wine samples, and the Royal Norwegian Council for Scientific and Industrial Research for a postdoctoral fellowship (M. Oehme).     

Determination of lead in igneous rocks by differential pulse anodic stripping voltammetry at an HMDE

A versatile and sensitive voltammetric method has been used for the determination of lead in seven USGS standard rocks and in two CRPG (Centre des Recherches Pétrografiques et Géochimiques, Nancy) standard rocks. The results, showing satisfactory precision and accuracy, are discussed with respect to the sample treatment and the voltammetric method.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10⁻⁸ to 1×10⁻⁶ mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10^–8 to 1×10^–6 mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

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.     

Determination of cadmium in sewage sludge by differential pulse anodic stripping voltammetry

A procedure was developed for the determination of cadmium in sewage sludge by differential pulse anodic stripping voltammetry. A sodium peroxide fusion carried out in zirconium crucibles was found to give satisfactory results, based on analysis of standard reference materials. Samples collected from the municipal sludge lagoon in Fort Wayne, Indiana were found to have cadmium abundances ranging from 120 to 250 ppm, with most samples falling in the 120 to 170 ppm range. Interference from zinc is easily eliminated by carrying out the deposition step at -0.95 V vs. Ag/AgCl. Lead-to-cadmium ratios as high as 50:1 (ppm basis) have no effect on the height of the cadmium peak.