Simultaneous determination of trace-levels of alloying zinc and copper by semi-mercury-free potentiometric stripping analysis with chemometric data treatment

Assays of copper and zinc in brass samples were performed by semi-mercury free potentiometric stripping analysis (S-MF PSA) using a thin-film mercury covered glassy-carbon working electrode and dissolved oxygen as oxidizing agent during the stripping step. The stripping peak transients were resolved by chemometrics, which enabled simultaneous determination of both the copper and the zinc concentrations, thereby eliminating the conventional necessary pretreatment of the sample solution, such as initial addition of Ga(III) or solvent extraction of copper. The brass samples were diluted by factors in the range 2 · 10⁴– 5 · 10⁵ which resulted in quantification of the copper and of zinc contents comparable to the specified values within 10%. On the basis of the chemometric treatment, an empirical expression is deduced relating the stripping time to the recorded potential. Received: 23 December 1997 / Revised: 25 February 1998 / Accepted: 28 February 1998     

电位溶出分析法同时测定锡, 铅, 铜

本文应用电位溶出分析法进行同时测定锡、铅和铜的研究。结果发现在草酸溶液中锡、铅和铜有分离清晰的平台,其溶出讯号与浓度呈线性关系,可用于定量分析。用这一方法测定了某些罐头食品中痕量锡、铅和铜,获得满意的结果。     

Simultaneous determination of lead and thallium by potentiometric stripping

A potentiometric stripping analysis procedure has been developed for the simultaneous determination of lead and thallium in chloroacetate-chloride medium. This procedure allows the determination of lead or thallium concentrations as low as 10 ng ml . The method is precise, and applicable to the determination of lead and thallium in sea-water.     

Computerized potentiometric stripping analysis for the determination of cadmium,lead, copper and zinc in biological materials

Two different types of tinned mussels and a bovine liver reference sample have been analyzed for Zn, Cd, Pb and Cu by means of computerized potentiometric stripping analysis and atomic absorption spectrometry. The samples were digested by two different procedures, one employing nitric acid only and the other employing nitric and perchloric acids. It is shown that computerized stripping analysis can be used in samples containing high concentrations of electroactive organic nitro compounds, without sample deoxygenation.     

Simultaneous determination of cadmium and lead in urine by means of computerized potentiometric stripping analysis

In computerized potentiometric stripping analysis for cadmium and lead in urine the samples are acidified with hydrochloric acid to a total concentration equal to 0.5 M. The sample is pre-electrolyzed at —1.25 V vs. SCE for 2 min without prior sample heating or deoxygenation, the working electrode being a mercury pre-coated glassy-carbon electrode. The lead and cadmium concentrations are evaluated by means of standard addition. Detection limits are 1 nM for both elements. Results obtained by potentiometric stripping analysis and by solvent extraction/atomic absorption are compared for samples from unexposed persons and from one patient under penicillamine treatment. The relative merits of the potentiometric stripping, anodic stripping and atomic absorption techniques are discussed.     

Lead determination in wine by potentiometric stripping analysis

Summary Computerized potentiometric stripping analysis (PSA) was used for lead determination in wine samples. In this method sample preparation before determination is limited to dilution with an appropriate supporting electrolyte (0.5 mol/l HCl and 40 mg/l Hg²⁺). Due to the very high sensitivity, the time needed for one determination can be reduced to 2 min. The method was tested by lead determination in different wines, different concentration ranges and in one European interlaboratory comparison organized by BCR. Using PSA it is possible to simultaneously determine cadmium, lead and copper in wine. For other elements such as Bi, Tl, Hg, Sn, As, Zn the determination procedures are under development. The PSA equipment is available on the market, small in size, relatively cheap and it does not require any special installation such as gas or cooling water.     

Determination of germanium by potentiometric stripping analysis and adsorption potentiometric stripping analysis

Potentiometric stripping analysis was applied to determination of germanium(IV) in 0.2M NH₃-NH₄Cl (pH 8.4) buffer solution at −1.8 V (vs. Ag/AgCl), with dissolved oxygen or Hg(II) as oxidant. The sensitivity was 8.5 × 10⁻⁹M in the presence of 2.0 × 10⁻⁵M Hg(II) with plating for 15 min after deaeration for 20 min. Cyclic voltammetry revealed that GE(IV) å Ge at the surface of the mercury-film electrode in a one-step irreversible reduction reaction, and the Ge at the electrode was oxidized by dissolved oxygen in the solution. The presence of complexing agents such as Alizarin Red (ARS), which forms a Ge(IV) complex adsorbed at the electrode, improved the sensitivity by one order of magnitude. The presence of adsorption was revealed by the temperature coefficient, the electrocapillary curve and cyclic voltammetry. Ge-containing samples were analysed by the proposed methods and agreement with the results obtained by other methods was excellent.     

Simultaneous determination of copper, zinc and lead by adsorptive stripping voltammetry in the presence of Morin

A sensitive and selective method for the simultaneous determination of copper, zinc and lead is presented. The method is based on the adsorptive accumulation of 2′,3,4′,5,7-pentahydroxyflavone (Morin) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. Optimal analytical conditions were found to be Morin concentration of 2.0 μM, pH of 4.0, and an adsorption potential at −500 mV versus Ag/AgCl. With an accumulation time of 60 s, the peak currents are proportional to the concentration of copper, lead and zinc over the 1 to 60, 0.3-80 and 1-70 ng ml⁻¹ range with detection limits of 0.06, 0.08 and 0.06 ng ml⁻¹, respectively. The procedure was applied to the simultaneous determination of copper, lead and zinc in some real and synthetic artificial real samples with satisfactory results.     

Simultaneous determination of trace amounts of zinc, lead and copper in rum by anodic stripping voltammetry

The determination of traces of Zn, Pb and Cu in rum samples by anodic stripping voltammetry without previous treatment or addition of a supporting electrolyte, using a hanging mercury drop electrode, is described. The choice of an appropriate stripping voltammetric method and deposition potential minimizes the influence of the organic content and ensures good reproductibility of the measurements. The reliability of the method was tested by comparing the results with those given by absorption spectrometry, the differences being about 10%. The method allows heavy metal ions to be determined in the mug l(-1) concentration range.     

Flow injection potentiometric stripping analysis and potentiometric stripping coulometry

Summary Potentiometric Stripping Analysis is used as a detection method for Flow Injection Analysis. A wall-jet glassy carbon disc electrode is applied for the determination of zinc, cadmium, and lead. Microliter samples are sufficient for high-speed determination in the ng-range. The sample throughout is up to 180 per hour depending on the metal ion concentration. The influence of various parameters on the stripping time is investigated.In addition the new concept of Potentiometric Stripping Coulometry is presented. Based on Faraday's law the measured stripping time can be used to calculate the mass of deposited metal. Provided that the deposition is complete the value found is identical to the mass totally present in the sample. Using lead as an example the accuracy of the determination is demonstrated for the wall-jet electrode. The application of a porous carbon felt electrode increases the speed of deposition. Optimum parameters are given for exhaustive depletion.

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Fließinjektion zur potentiometrischen Stripping-Analyse und potentiometrischen Stripping-Coulometrie

Zusammenfassung Die potentiometrische Stripping-Analyse wird zur Detektion in der Fließinjektionsanalyse eingesetzt. Zur Bestimmung von Zink, Cadmium und Blei wird eine Wall-Jet Scheibenelektrode aus Glaskohlenstoff verwendet. Bei Injektion vonl-Mengen sind Schnellbestimmungen im ng-Bereich möglich. Je nach Metallionenkonzentration läßt sich ein Probendurchsatz von bis zu 180 pro Stunde erreichen. Der Einfluß verschiedener Parameter auf die Strippingzeit wird untersucht. Weiterhin wird das neue Konzept der potentiometrischen Stripping-Coulometrie vorgestellt. Die abgeschiedene Metallmasse kann aus der gemessenen Strippingzeit und dem zu berechnenden Oxydationsstrom ermittelt werden. Nach vollständiger Abscheidung ist diese Masse der gesamten in der Probe enthaltenen Masse gleich. Am Beispiel einer Bleibestimmung mit der Wall-Jet-Elektrode wird die Richtigkeit dieser Methode belegt. Durch die Verwendung einer Carbonfilzelektrode wird die Geschwindigkeit der vollständigen Abscheidung erhöht. Der Einfluß von Flußrate und injizierter Menge wird untersucht.

     

Determination of zinc,cadmium, lead and copper in sea water by means of computerized potentiometric stripping analysis

Water samples from the Arctic Sea were analyzed by the potentiometric stripping technique. Lead(II) and cadmium(II) were determined after pre-electrolysis for 32 min at—1.1 V vs. Ag/AgCl, the detection limits being 0.06 and 0.04 nM, respectively. Zinc(II) was determined after the addition of gallium(III) by pre-electrolysis for 16 min at —1.4 V vs. Ag/AgCl, the detection limit being 0.25 nM. Problems in the determination of copper(II) at the very low concentrations found in oceanic waters are outlined. The average zinc(II), cadmium(II) and lead(II) concentrations in eight different samples were 2.5, 0.16 and 0.10 nM as determined by potentiometric stripping analysis and 1.9, 0.16 and 0.09 nM as determined by solvent extraction/atomic absorption spectrometry. The advantages of this computerized technique for the analysis of sea water are discussed.     

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).     

Simultaneous determination of lead,copper, cadmium and zinc in pure zirconium metal by differential-pulse anodic stripping voltammetry

Zirconium metal (ca. I g) was dissolved in hydrofluoric acid, excess of which was removed by fuming with sulphuric acid. An aliquot of this solution was treated with sodium citrate and adjusted to pH 4.5. Lead, copper and cadmium were deposited on the hanging mercury drop electrode by applying a potential of ?0.8 V vs. Ag/AgCl for 1 min and anodic stripping voltammograms were recorded; the anodic peaks appeared at ?0.51, ?0.14 and ?0.67 V, respectively. In a separate run, zinc was deposited at ?1.2 V and the stripping peak appeared at ?1.1 V. Standard additions were used to quantify these impurities at levels in the low mg kg^?1 range, with relative standard deviations of 5–11%.     

Simultaneous determination of sugars and organic acids in aged vinegars and chemometric data analysis

Aceto Balsamico Tradizionale of Modena (ABTM) is a typical product (PDO denomination) of the province of Modena produced by cooked grape must which undergoes a long ageing period (at least 12 years) in series of wooden casks (batterie). The study of the transformations of this product during ageing is extremely relevant in order to control the authenticity of ABTM towards succedaneous products and mislabelling of age.

This paper presents the results of the investigation of sugars and fixed organic acids in ABTM samples of different ages, coming from different batterie. The analytes were simultaneously determined by a gas chromatographic method optimised for this peculiar matrix.

The method shows good separation and resolution of the investigated chemical species and allows their determination in the concentration ranges reported in brackets: malic (7.6–15.5 g kg⁻¹), tartaric (4.0–9.7 g kg⁻¹), citric (0.6–1.5 g kg⁻¹) and succinic (0.36–0.62 g kg⁻¹) acid and glucose (153–294 g kg⁻¹), fructose (131–279 g kg⁻¹), xylose (011–0.39 g kg⁻¹), ribose (0.078–0.429 g kg⁻¹), rhamnose (0.061–0.195 g kg⁻¹), galactose (0.136–0.388 g kg⁻¹), mannose (0.41–1.46 g kg⁻¹), arabinose (0.33–1.00 g kg⁻¹) and sucrose (0.46–6.84 g kg⁻¹), with mean associated errors ranging from 5 to 19% depending on the analytes.

Moreover, the recovery values are always satisfactory, being close to one for most of the analytes.

Furthermore, in order to assess the degree of variability of the different analytes content with vinegar ageing and the similarity/dissimilarity among series of casks a three-way data analysis method (Tucker3) is proposed. The chemometric technique applied on the data set shows differences between the samples on the bases of their different ageing period, and between the batterie, which traditionally have an own peculiar production procedure.     

Intermetallic compounds and the determination of copper and zinc by anodic stripping voltammetry

The intermetallic CuZn compounds produced during the simultaneous deposition of copper and zinc at a preformed mercury film electrode were studied. Over a wide range of metal concentration ratios, the real concentrations of metals in the amalgam were calculated from the peak areas obtained by anodic stripping voltammetry. The results indicate the formation of CuZn (insoluble) and CuZn2 (soluble) compounds with K_so=5×10^?4 and β₂=100, respectively. The electrodeposition potential of ?0.85 V vs. SCE for the reduction of copper in presence of zinc is confirmed as correct.     

Simultaneous determination of copper and lead in ethanol fuel by anodic stripping voltammetry

The presence of trace metals in car fuels plays an important role in the engine maintenance. In addition, these metals contribute for the environmental contamination in big cities and their control is necessary. Square Wave Stripping Voltammetry (SWSV) is a very sensitive technique for elemental trace determination and was applied for ethanol fuel analysis. The first studies were done searching for the best conditions for copper determination in alcoholic medium, utilizing gold electrodes. During these studies, the possibility of the simultaneous determination of copper and lead in the same experiment was observed. Two procedures for the analysis of these metals were adopted: The direct quantification of metals in alcohol–water mixtures and a second way that involves the evaporation of the organic solvent and re-suspension of the ions with water+electrolyte. Good recovery values were obtained for synthetic samples spiked with known amounts of metals. The results obtained for the two methods were in good agreement. The detection limits for copper and lead in 75% ethanol–water ratio solution were calculated as 120 and 235 ng l⁻¹, respectively, for 15-min deposition time.     

Interlaboratory quality control for lead determination in wine by potentiometric stripping analysis

Summary Computerized potentiometric stripping analysis (PSA) was used for the determination of lead in wine samples. With this analytical method the sample preparation is limited to dilution with an appropriate supporting electrolyte (0.5 mol/l HCl and 40 mg/l Hg²⁺). Due to very high sensitivity the time needed for one determination can be reduced to 2 min. This method for lead determination in wine was compared with results from voltammetry and ETAAS from various laboratories participating in two BCR studies. With PSA it is possible to determine cadmium, lead and copper in wine after a single dilution with an appropriate supporting electrolyte. For other elements such as Bi, Tl, Hg, Sn, As, Zn determination procedures are under development.     

Simultaneous determination of lead, cadmium and zinc in aerosols by anodic stripping voltammetry

Summary The simultaneous determination of lead, cadmium and zinc in air particulate matter by anodic stripping voltammetry is described. Optimum conditions for the anodic stripping of lead, cadmium and zinc were determined using ammonium tartrate buffer at pH 4.5. Interferences from other metals were not encountered and the estimations were reproducible within a standard deviation of ±10%. Low blank values and high sensitivity of the method allowed the determinations at sub-ppb levels with an electrolysis time of 3–10 min. The geometric mean concentrations of lead, cadmium and zinc at various locations in Greater Bombay during 1979 are also presented.

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Simultanbestimmung von Blei, Cadmium und Zink in Aerosolen durch anodische Stripping-Voltammetrie

Zusammenfassung Die optimalen Bedingungen für die Bestimmung von Pb, Cd und Zn unter Verwendung von Ammoniumtartratpuffer pH 4,5 wurden ausgearbeitet. Störungen durch andere Metalle traten bei den untersuchten Aerosolen nicht auf. Die Standardabweichungen lagen bei ±10%. Infolge niedriger Blindwerte und hoher Empfindlichkeit konnten Bestimmungen im sub-ppb-Bereich mit Elektrolysenzeiten von 3–10 min durchgeführt werden. Ein Überblick über die Konzentration der genannten Metalle in der Luft von Bombay wird gegeben.