Strategy for copper speciation in white wine by differential pulse anodic stripping voltammetry, potentiometry with an ion-selective electrode and kinetic photometric determination

Differential pulse anodic stripping voltammetry (DPASV), potentiometry with a copper ion-selective electrode and a kinetic photometric method were used to determine copper species in white wines. The kinetic method is based on the catalytic effect of labile copper(II) species on the oxidation of 3-hydroxybenzaldehyde azine by potassium peroxidisulfate in an ammonical medium at room temperature. The total copper concentrations were determined by flame atomic absorption spectrometry. Free copper(II) ions, labile and tightly bound copper species could be quantified in 16 non pre-treated wine samples. Received: 13 August 1996 / Revised: 28 October 1996 / Accepted: 29 November 1996     

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).     

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.     

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 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.     

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.      

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.     

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.     

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     

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 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 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

     

Subtractive differential pulse anodic stripping voltammetry at a stationary mercury-coated glassy carbon electrode

The application of subtractive mode differential pulse anodic stripping voltammetry (SDPASV) at a stationary mercury-coated glassy carbon electrode for the analysis of labile Zn(II), Cd(II), Pb(II) and Cu(II) is described. It is shown that the method has an improved sensitivity to Cu(II) owing to elimination of high background currents normally encountered in normal mode DPASV at the TFME. The sensitivity limits of the present method to Cd(II) and Cu(II) is estimated to be 0.025 and 0.067 ppb respectively, when a 2 min deposition time is used. It is suggested that the high sensitivity of the method coupled to the relative simplicity of the stationary electrodes could make the method useful in environmental and natural water studies.     

Determination of lead, cadmium, copper and zinc in human tissues by differential pulse anodic stripping voltammetry

Summary A convenient electroanalytical technique for the simultaneous determination of lead, cadmium, copper and zinc in human blood and teeth is described. The method is based on differential pulse anodic stripping voltammetry at the static mercury drop electrode (SMDE). Optimum conditions for the anodic stripping of Pb, Cd, Cu and Zn were determined using ammonium acetate and dilute nitric acid (pH 2) as electrolytes. Interferences from other metals were not observed and the estimations were reproducible within a standard deviation of±4%. Low blank values and high sensitivity of the method allowed the determinations at sub-ppb levels with an electrolysis time of 1–3 min. The accuracy of the method has been tested by comparison with the results obtained by mass spectrometry and atomic absorption spectrometry. The results and findings are discussed in brief.

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Bestimmung von Blei, Cadmium, Kupfer und Zink in menschlichen Geweben mit Hilfe der Differentialpuls-Anodic Stripping Voltammetrie

Zusammenfassung Eine vorteilhafte elektroanalytische Methode zur Bestimmung von Pb, Cd, Cu und Zn in menschlichem Blut und in Zähnen wird beschrieben. Das Verfahren beruht auf der Differentialpuls-Anodic Stripping Voltammetrie an der statischen Quecksilbertropfelektrode. Mit Hilfe von Ammoniumacetat und verdünnter Salpetersäure (pH 2) als Trägerelektrolyten wurden die optimalen Bedingungen ausgearbeitet. Störungen durch andere Metalle wurden nicht beobachtet. Die Standardabweichung betrug ±4%. Infolge der niedrigen Blindwerte und der hohen Empfindlichkeit konnten Bestimmungen im Sub-ppb-Bereich mit Elektrolysezeiten von 1–3 min durchgeführt werden. Die Genauigkeit der Methode wurde durch Vergleich mit massenspektrometrischen und AAS-Untersuchungen bewiesen. Die Ergebnisse werden kurz diskutiert.

     

The determination of lead,copper and cadmium by anodic stripping voltammetry at a mercury thin-film electrode

The determination of lead, copper and cadmium by anodic stripping voltammetry at a wax-impregnated graphite electrode, pre-plated with mercury, has been investigated. Electrode preparation and cell design are discussed, and the effects of mercury loading and sample pH on electrode sensitivity are described. Detection limits and precision on aqueous samples are reported. Calibration graphs are linear for lead and cadmium, but non-linear for low concentrations of copper. The depression of peak current and shift of peak potential for copper in chloride media are described and an explanation is proposed. Precision and recovery of metal additions are reported for digested samples of whole blood.     

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.     

The determination of zinc,cadmium, lead and copper in human hair by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode after nitrate fusion

Samples of hair are digested with nitric acid and fused with alkali metal nitrates, prior to the determination of Zn, Cd, Pb and Cu by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode. Recoveries from spiked samples range from 91 to 101%. Relative standard deviations vary from 2.6 to 13%, depending on the metal and sample source. Some causes of poor reproducibility are discussed.