Determination of free and total copper and lead in wine by stripping potentiometry

Stripping potentiometry has been employed for the measurement of the labile and total copper concentrations in white wine. Conditions have been optimised for a supporting electrolyte consisting of 1.0 mol/L hydrochloric acid and 0.5 mol/L calcium chloride. Mercury(II) was found to be a more suitable oxidant than O₂ and, for the determination of the labile concentrations, this required the use of medium exchange. With lead, O₂ proved to be an efficient oxidant for the stripping step and this allowed the direct measurement in the wine without the need for medium exchange. It was observed that red wine rapidly binds added lead, demonstrating that wine has a high complexation capacity for lead. A similar complexation effect was also observed for white wine, but the degree of lead complexation was less than that for red wine. The impact of this lead complexation effect for the use of standard additions is discussed.     

Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

Cyclic and stripping voltammetry of tin at mercury hanging drop and film electrodes in acidic o-diphenol media in the presence of lead and cadmium

The influence of catechol, gallic acid and tiron on the voltammetric behaviour of tin(IV) in the presence of lead(II) and cadmium(II) was investigated at hanging drop and mercury film electrodes in perchloric acid, oxalic acid and formate supporting electrolytes. Under cyclic conditions, well separated peaks of tin, lead and cadmium are obtained in oxalic acid and formate solutions containing gallic acid or catechol; tiron suppresses the tin peaks significantly. The efficiency of the deposition of tin in the presence of catechol or gallic acid is less than that of lead, particularly at long deposition time. The best separation of the stripping peaks of tin, lead and cadmium is obtained in oxalic acid solution containing gallic acid or catechol. In perchloric acid solution containing gallic acid or catechol the second peak corresponding to tin oxidation is useful for determinations of tin in the presence of lead. Tin(IV) at the 10^-8 mol l^-1 level can be detemined in various salt solutions and in water samples in the presence of five-fold amounts of lead and cadmium.     

Determination of lead in whole blood with a simple flow-injection system and computerized stripping potentiometry

An automated (24 samples/hour) procedure is described for the determination of lead (0–1000 μg l^?1) in human blood based on flow-injection stripping potentiometry. The samples are diluted 20-fold with 0.5 M hydrochloric acid containing 100 mg l^?1 mercury and 40 μg l^?1 cadmium (II), and a 1.1 ml aliquot is injected into the flow system. With a mercury-coated carbon fibre as working electrode, lead (II) is determined by using cadmium (II) as internal standard and a calibration graph prepared from bovine blood. Analyses of two human blood reference samples yielded results of 335±37 and 691±24 μg l^?1 lead, the certified values being 332 and 663 μg l^?1, respectively.     

Experimental and computational study of species formed during electrochemical stripping oxidation of copper in chloride media determination of copper(II) in the ng l(-1) range by stripping potentiometry

A novel glassy carbon electrode design, permitting medium exchange in batch mode without loss of electrode potential control, has been used for the study of copper(I) and copper(II) species formed during constant current stripping oxidation of copper in chloride media. It was found that copper(II) species dominated at chloride concentrations below about 1 mM and that soluble copper(I) species dominated at chloride concentrations above about 100 mM. In the concentration range 1-100 mM, soluble copper(I) and copper(II) species are formed as well as solid copper(I) chloride, the latter giving rise to a split peak as it is further oxidised to copper(II). The experimental results agreed satisfactorily with computer calculated equilibria data using the haltafall program. The medium exchange procedure has, furthermore, been used for the determination of copper(II) in seawater reference samples, 7.5 M ammonium acetate/2.5 M acetic acid being used as stripping medium. The detection limit, after 15 min of electrolysis, was found to be 6 ng l(-1) (0.10 mM) and the relative precision 6-10%.     

Determination of lead and cadmium in biological samples by potentiometric stripping analysis

Summary The determination of lead and cadmium in biological materials was carried out by potentiometric stripping analysis. Supporting electrolyte was a mixture of NaCl and HCl. In the presence of 4% lumatom in methanol, oxidation potentials of –0.46 V for Pb and –0.68 V for Cd were found (vs. SCE). The method was applied to different standard reference materials (leaves, needles, hair) and was also compared with the differential pulse anodic stripping technique. The latter presented considerable difficulties, in particular by the interference of oxygen.

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Bestimmung von Blei und Cadmium in biologischem Material durch potentiometrische Stripping-Analyse

Zusammenfassung Als Trägerelektrolyt diente bei diesem Verfahren ein Gemisch von NaCl und HCl. In Gegenwart von 4% Lumatom in Methanol wurden Oxidationspotentiale von –0,46 V für Pb und –0,68 V für Cd (gegen SKE) erhalten. Die Methode wurde auf verschiedene Referenzmaterialien (Laub, Nadeln, Haar) angewendet und auch mit der Differentialpuls-Anodic Stripping-Analyse verglichen. Bei der letzteren ergaben sich größere Schwierigkeiten, hauptsächlich durch störenden Sauerstoff.

     

Determination of traces of purine by cathodic stripping voltammetry at the hanging copper amalgam drop electrode

In the presence of purine, the copper(II)/copper(Hg) couple splits into copper(II)/copper(I) and copper(I)/copper(Hg) couples, which form two well-separated systems of peaks under voltammetric conditions. The copper(I)/purine complex adsorbs on the electrode surfacer and can be deposited on the electrode surface by electroreduction of copper(II) ions at the HMDE or by electro-oxidation of the hanging copper amalgam drop electrode (HCADE). The deposit can be stripped either cathodically or anodically over the pH range 2–9. The cathodic stripping variant at the HCADE, in solution with pH 2, offers the best results, with linear response for the range 5 × 10^?9–1.5 × 10^?7 mol dm^?3 purine after an accumulation time of 3 min. The detection limit found with the HMDE in the presence of copper(II) ions is higher.     

Determination of cadmium, lead and copper in wine by potentiometric stripping analysis

A procedure for the determination of Cd, Pb and Cu in different wine samples after simple sample preparation on a mercury film electrode (MFE) by potentiometric stripping analysis (PSA) is presented. In 150 German wine samples collected in 1993/94 the following values were found: Cd mean: 0.63 ng/mL (range: 0.003– 0.98 ng/mL); Pb mean: 50 ng/mL (range: 4–254 ng/mL); Cu mean: 250 ng/mL (range: 50–394 ng/mL).     

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.     

Simultaneous determination of tin and lead by a.c. anodic stripping voltammetry at a hanging mercury drop electrode sensitized by cetyltrimethylammoniu

The influence of cetyltrimethylammonium bromide (CTAB) on the simultaneous determination of tin(IV) and lead(II) by anodic stripping voltammetry at a hanging mercury drop electrode (HMDE) in a 0.1 M hydrochloric acid—0.1 M oxalic acid medium was studied using d.c. and a.c. stripping. In the presence of CTAB, tin and lead show voltammetric peaks separated by 100 mV, the sensitivity depending on the concentration of CTAB. The best conditions for the simultaneous determination of both elements (2 × 10^-3 M) were found. A method is proposed for the determination of tin in the presence of lead and three procedures are given for the determination of lead in the presence of tin.     

Determination of naringin in grapefruit juice by cathodic stripping differential pulse voltammetry at the hanging mercury drop electrode

A highly sensitive cathodic stripping voltammetric method for the determination of naringin is presented. It is based on the formation and accumulation of two naringin–mercury complexes at the electrode surface, followed by reduction of the surface species during a differential pulse voltammetric scan. The cathodic stripping responses at −0.25 V and −0.42 V, are evaluated with respect to various experimental conditions, such as composition and pH of the supporting electrolyte, naringin concentration, accumulation potential and preconcentration time. The new method is suitable for the determination of naringin concentrations between 0.1 mg l⁻¹ (1.72×10⁻⁷ mol l⁻¹) and 40 mg l⁻¹ (6.88×10⁻⁵ mol l⁻¹). A 3σ limit of detection of 32 μg l⁻¹ (55 nmol l⁻¹) can be reached. The relative standard deviation (r.s.d.) is <1.5%. Recovery experiments yielded a mean recovery of 97% (r.s.d.=4.1%). The application of the procedure to the selective determination of naringin in grapefruit juice is demonstrated.     

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).     

Determination of traces of selenium(IV) by cathodic stripping voltammetry at the hanging mercury drop electrode

Conditions convenient for the determination of traces of seIenium(IV) by cathodic stripping technique are described. Several electrolytes were tested. Three procedures are given in which the troublesome splitting of the stripping peak is eliminated. Suitable conditions include perchloric acid solution at elevated temperature, hydrochloric acid solution after preconcentration at zero current, and perchloric acid solution containing a small amount of iodide. The detection limits are 5 × 10^-9, 2 × 10^-9 and 5 × 10^-10 mol dm^-3, respectively. The time required for the entire procedure is about 30 min starting with a soluble seIenium(IV) sample.     

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).     

Low-level determination of silicon in steels by anodic stripping voltammetry on a hanging mercury drop electrode

The sensitive differential pulse anodic stripping voltammetry (DPASV) proposed originally by Ishiyama et al. (2001) has been revised and improved to allow the accurate measurement of silicon on a hanging mercury drop electrode (HMDE) instead of a glassy carbon electrode. We assessed the rate of formation of the partially reduced β-silicododecamolybdate and found that metallic mercury promotes the reaction in the presence of a large concentration of Fe³⁺. The scope of the method has been broadened by carrying out the measurements in the presence of a constant amount of Fe³⁺. The limit of detection (LOD) of the method described in the present paper is 100 μg Si g⁻¹ of steel, with a relative precision ranging from 5% to 12%. It can be further enhanced to 700 ng Si g⁻¹ of steel provided the weight of the sample, the dilution factors, the duration of the electrolysis and the ballast of iron are adequately revised. The tolerance to several interfering species has been examined, especially regarding Al³⁺, Cr³⁺ and Cr VI species. The method was validated using four low-alloy ferritic steels certified by the National Institute of Standards and Technology (NIST). Its application to nickel base alloys as well as to less complicated matrixes is straightforward. It has also been successfully applied to the determination of free silicon into silicon carbide nano-powder.