Elimination of iron interference in the differential pulse anodic stripping voltammetry of copper

The interference of iron(III) on the quantitation of copper(II) in citrate media by differential-pulse anodic stripping voltammetry can be completely removed by lowering the pH to 1.5 with 70% perchloric acid.     

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 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.     

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 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.     

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 copper in niobium in the sub-ppm range by differential pulse anodic stripping voltammetry

Summary Low levels of copper in niobium may be determined rather rapidly and accurately by differential pulse anodic stripping voltammetry (DPASV). Three sigma detection limit of about 10 ppb can be achieved with a stripping time of 10 min. Wire, sheet and rod samples are dissolved by anodic oxidation in methanol and powder samples in a mixture of hydrofluoric acid and nitric acid. The methanolic solution is transferred into an aqueous one by the addition of an aqueous 1 M oxalic acid solution and by the evaporation of the methanol. The oxalic acid and oxalic acid + hydrofluoric acid solutions, respectively, are analysed by DPASV without any separation of the matrix. Only a few metals interfere with the copper signal when they are present in large excess, but these interferences can be overcome by changing the electrolyte, the solution or the pH. — This method can also be applied to the determination of copper in niobium salts that are soluble in oxalic acid or in hydrofluoric acid.

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Bestimmung von Kupfer in Niob im Sub-ppm-Bereich durch inverse differenzielle Pulspolarographie

Zusammenfassung Niedrige Gehalte an Kupfer in Niob können ziemlich schnell und genau mit Hilfe der inversen differenziellen Pulspolarographie bestimmt werden. Mit einer Anreicherungszeit von 10 min erreicht man eine Drei-Sigma-Nachweisgrenze von ungefähr 10 ppb. Draht-, Platten- und Stangenproben werden durch anodische Oxidation in Methanol und Pulverproben in einer Mischung aus Flußsäure und Salpetersäure gelöst. Die methanolische Lösung wird durch Zugabe von 1 M Oxalsäure und durch Verdampfen des Methanols in eine wäßrige Lösung überführt. Die oxalsaure Lösung ohne bzw. mit Flußsäure wird mit Hilfe der inversen differentiellen Pulspolarographie ohne Abtrennen der Matrix analysiert. Nur wenige Metalle stören die Kupferstufe, wenn sie in großem Überschuß zugegen sind. Man kann diese Störungen u.a. durch Änderung des Elektrolyten, durch Lösungswechsel oder pH-Änderung beseitigen. — Diese Analysenmethode kann auch bei der Bestimmung von Kupfer in Niobsalzen angewandt werden, die sich in Oxalsäure oder Flußsäure lösen.

Presented in part at the International Symposium on Microchemical Techniques, Davos, Switzerland, May 22–27, 1977     

Determination of thallic and thallous ions by differential pulse anodic stripping voltammetry without preliminary separation

The simultaneous determination of thallic and thallous ions, without preliminary separation, has been achieved by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode. The electrochemical activity of thallic ions in 0.2M EDTA at pH 4.5 +/- 0.2 is inhibited by the addition of 0.01% poly(ethyleneglycol) of M.W. 20,000 (PEG 20,000). When the electrolyte also contains ascorbic acid at 0.01M concentration, the sum of thallic and thallous species can be determined.     

Determination of trace amounts of morphine in human plasma by anodic adsorptive stripping differential pulse voltammetry

New adsorptive anodic differential pulse stripping voltammetry method for the direct determination of morphine at trace levels in human plasma of addicts is proposed.The procedure involves an adsorptive accumulation of morphine on a HMDE,followed by oxidation of adsorbed morphine by voltammetry scan using differential pulse modulation.The optimum conditions for the analysis of morphine are pH 10.5,Eacc of -100 mV（vs.Ag/AgCl）,and tacc of 120 s.The peak current is proportional to the concentration of morphine,and a Linear calibration graph is obtained at 0.01-3.10μg mL^-1.A relative standard deviation of 1.06%（n=5）was obtained,and the limit of detection was 3 ng mL^-1.The capabiLity of the method for the analysis of real samples was evaluated by the determination of morphine in spiked human plasma and addicts human plasma with satisfactory results.     

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 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.     

Indirect determination of lutetium by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode

Lutetium has been determined by differential pulse anodic stripping voltammetry in an acidic solution containing Zn-EDTA. Lutetium (III) ions liberated zinc (II), which was preconcentrated on a hanging mercury drop electrode and stripped anodically, resulting in peak current linearly dependent on lutetium (III) concentration. Less than 0.4 ng mL⁻¹ lutetium could be detected after a 2 min deposition.      

Determination of antimony (III) and (V) by differential pulse anodic stripping voltammetry

Re-evaluation of DPASV procedures for determining low levels of Sb (III) and Sb (V) in solution identified several problem areas, e.g. anomalous ASV behaviour, possible formation of an intermediate valency state during the analytical cycle, and chemical interactions in acidified test solutions containing both valency states. Specific determination of Sb (III) can be achieved using base solutions composed of 0.2M HCl (detection limit 10 nM) or acetic acid/acetate buffer (detection limit 600 nM). For the determination of Sb (V), analysis in 2M HCl is recommended [with response in 0.2M HCl being used to correct for any Sb (III) present].     

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.     

Determination of thallium in soils by differential pulse anodic stripping voltammetry by means of a mercury film electrode

Trace amounts of thallium can be determined in soils by differential pulse anodic stripping voltammetry with a mercury film electrode. The mercury film is plated ex situ on a glassy carbon surface. By using a supporting electrolyte of ascorbic acid and EDTA at pH 4.5 and the optimum electrolysis potential, interferences from lead and other metal ions can be eliminated. The method does not require any separation of thallium from the matrix. The results are in satisfactory agreement with those obtained by graphite furnace atomic absorption spectrometry.