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).     

Simultaneous determination of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry on a stannum film electrode

A stannum film electrode has been developed for the simultaneous determination of trace levels of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry (DPASV). The stannum film electrode was generated in situ by depositing simultaneously the stannum film and the metals obtained by reduction of Cd(II) and Cr(III) at −1.4 V on a glassy carbon electrode. Then, the reduced products were oxidized by scanning the potential of the electrode from −1.4 to −0.4 V using DPASV. The electrode exhibited well-defined and separated stripping signals for both metals accompanied with a low background contribution. The possible mechanism of this design was proposed. Under the optimized working conditions, the detection limit was 2.0 and 1.1 μg l⁻¹ for Cr(III) and Cd(II) at a deposition time of 3 min. Finally, the stannum film electrode was successfully applied to the determination of Cd(II) in tap water with satisfactory results.     

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     

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.

     

Comparison of digestion procedures for the determination of heavy metals (Cd, Cu, Pb) in blood by anodic stripping voltammetry

Summary The simultaneous determination of cadmium, lead and copper in whole blood by anodic stripping voltammetry is described. Different digestion procedures given in literature were examined. In addition, a sample pretreatment method which did not involve digestion was studied. Based on the experience with these methods two digestion procedures were developed. They utilize digestion with mixtures of nitric, perchloric and sulphuric acids, with and without pressure, respectively. Both methods are suitable for routine analysis of about 20 blood samples per day. Special attention was focussed on the completeness of the digestion, and the magnitude of the blank values. Low blank values and a high sensitivity allowed the determination of cadmium at the sub-ppb level with an electrolysis time of 5 min. The methods, which were controlled by recovery tests, were used to analyze blood samples from unexposed persons, and from workers suspected of exposure to cadmium.

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Vergleich von Aufschlußverfahren für die Bestimmung von Schwermetallen (Cd, Cu, Pb) in Blut durch Anodic Stripping Voltammetrie

Zusammenfassung Verschiedene in der Literatur beschriebene Aufschlußverfahren wurden untersucht und zusätzlich ein Probenvorbereitungsverfahren ohne Aufschluß geprüft. Aufgrund der mit diesen Methoden gewonnenen Erfahrungen wurden zwei Aufschlußverfahren entwickelt, bei denen Mischungen von Salpeter-, Perchlor- und Schwefelsäure mit und ohne Anwendung von Druck eingesetzt werden. Beide Methoden eignen sich für die Routineuntersuchung von etwa 20 Blutproben je Tag. Besondere Aufmerksamkeit wurde der Vollständigkeit des Aufschlusses und der Größe der Blindwerte gewidmet. Niedrige Blindwerte und hohe Empfindlichkeit erlaubten die Bestimmung von Cadmium im sub-ppb-Bereich mit einer Elektrolysezeit von 5 min. Die Methoden wurden durch Wiederauffindungstests geprüft und für die Blutuntersuchung von Personen, die der Einwirkung von Cd ausgesetzt waren, sowie solchen, bei denen dies nicht der Fall war, angewendet.

     

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.      

Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry

A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb²⁺ and Cd²⁺ were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (−1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of −0.65 V (Cd²⁺) and −0.91 V (Pb²⁺) demonstrates the possibility of simultaneous determination of Pb²⁺ and Cd²⁺. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0×10⁻⁷-1.5×10⁻⁵ mol l⁻¹ (Pb²⁺) and 2.5×10⁻⁷-2.5×10⁻⁵ mol l⁻¹ (Cd²⁺), respectively. For 5 min preconcentration, detection limits of 1×10⁻⁸ mol l⁻¹ (Pb²⁺) and 4×10⁻⁸ mol l⁻¹ (Cd²⁺) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5×10⁻⁷ mol l⁻¹ Pb²⁺ and Cd²⁺ were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb²⁺) and 3.2% (Cd²⁺), respectively. Interferences by some metals were investigated. Only Ni²⁺ and Hg²⁺ apparently affected the peak currents of Pb²⁺ and Cd²⁺. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb²⁺ and Cd²⁺ in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.     

Automatic amperometric microtitration of barbiturates with mercury(II) at the glassy carbon electrode

Summary The amperometric, mercurimetric microtitration of barbiturates at the glassy carbon electrode with an improved model of an automatic recording titrator is described. The reduction of mercury at the glassy carbon electrode has been studied by automatic steady-state voltammetry. A new, two-phase titration (Na acetate/organic solvent) and two methods of which the medium (KNO₃ resp. Na acetate) of the titration has been described in literature, are compared with a macro reference titration. Phenobarbital, sodium phenobarbital, barbital, sodium barbital, sodium amobarbital and pentobarbital have been titrated. The two-phase titration is better than the other two methods for samples in the range of 10^–4–10^–5 M. The titration of 50 g of barbiturate is possible with a precision and accuracy of about 2%.

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Automatische amperometrische Mikrotitration von Barbituraten mit Quecksilber(II) an der glasartigen KohlenstoffelektrodeVergleich von Ein- und Zweiphasentitrationen

Zusammenfassung Für die Titrationen wurde ein verbesserter automatisch registrierender Titrator benutzt. Die Reduktion des Quecksilbers an der Kohlenstoffelektrode wurde mit Hilfe der automatischen steady-state Voltammetrie untersucht. Eine neuartige Zweiphasentitration (Naacetat/organ. Lösungsmittel) sowie zwei Verfahren in bekannten Medien (KNO₃ bzw. Na-acetat) wurden mit einer Makrotitration verglichen. Phenobarbital, Phenobarbitalnatrium, Barbital, Barbitalnatrium, Amobarbitalnatrium und Pentobarbital wurden titriert. Für den Konzentrationsbereich 10^–4 bis 10^–5 M ist das Zweiphasenverfahren am besten geeignet. Eine Titration von 50 g eines Barbiturats ist auf etwa 2% genau durchzuführen.

     

Determination of inorganic antimony species in seawater by differential pulse anodic stripping voltammetry: stability of the trivalent state

A simple method is described for the rapid and reliable determination of ultratrace concentrations of Sb(III) and Sb(V) in seawater by differential pulse anodic stripping voltammetry. It is based on the well-known dependence of Sb(III)/Sb(V) voltammetric response on acidity conditions. Under our optimised conditions (0.5 mol l⁻¹ HCl for Sb(III) and 5 mol l⁻¹ HCl for total Sb, respectively): (i) a detection limit of 11 ng l⁻¹ is obtained for a 10 min deposition time; (ii) no prior elimination of organic matter is needed; and (iii) antimony can be determined in the presence of natural copper levels. Particular care has been taken in order to understand the chemical processes taking place in all the solutions and reactions involved in the sampling and measuring procedures. Our results revealed the need to consider (i) the effect of photooxydation of synthetic and seawater samples on Sb speciation; and (ii) the stability of Sb(III) both in seawater samples and in the analytical solutions.     

Determination of mercury in ambient water samples by anodic stripping voltammetry on screen-printed gold electrodes

The applicability of commercial screen-printed gold electrodes (SPGEs) for the determination of Hg(II) in ambient water samples by square wave anodic stripping voltammetry has been demonstrated. Electrode conditioning procedures, chemical and instrumental variables have been optimized to develop a reliable method capable of measuring dissolved mercury in the low ng mL⁻¹ range (detection limit 1.1 ng mL⁻¹), useful for pollution monitoring or screening purposes. The proposed method was tested with the NIST 1641d Mercury in Water Standard Reference Material (recoveries 90.0–110%) and the NCS ZC 76303 Mercury in Water Certified Reference Material (recoveries 82.5–90.6%). Waste water samples from industrial origin and fortified rain water samples were assayed for mercury by the proposed method and by a reference ICP-MS method, with good agreement. Screen printing technology thus opens a useful way for the construction of reliable electrochemical sensors for decentralized or even field Hg(II) testing.     

Konduktometrische Bestimmung von Nickel(II)-, Kobalt(II)- und Kupfer(II)- Ionen aufgrund der Bildung von Pyridin-Rhodanid-Komplexen

Ohne Zusammenfassung

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Conduotometric determination of Ni(II), Co(II) and Cu(II) ions based on the formation of pyridine-rhodanide complexes

     

Lithium ions determination by selective pre-concentration and differential pulse anodic stripping voltammetry using a carbon paste electrode modified with a spinel-type manganese oxide

The use of selective pre-concentration and differential pulse anodic stripping voltammetry (DPASV) using a carbon paste electrode modified (CPEM) with spinel-type manganese oxide has been proposed for the determination of lithium ions content in natural waters. The new procedure is based on the effective pre-concentration of lithium ions on the electrode surface containing spinel-type Mn(IV) oxide with the reduction of Mn(IV) to Mn(III) and consequently the lithium ions intercalation (insertion) into the spinel structure. The best DPASV response was reached for an electrode composition of 25% (m/m) spinel-type MnO₂ in the paste, 0.1 mol l⁻¹ tris(hydroxymethyl)aminomethane (TRIS) buffer solution of pH 8.3, scan rate of 5 mV s⁻¹, accumulation potential of 0.3 V versus saturated calomel reference electrode (SCE), pre-concentration time of 30 s and potential pulse amplitude of 50 mV. In these experimental conditions, the proposed methodology responds to lithium ions in the concentration range of 2.8×10⁻⁶ to 2.0×10⁻³ mol l⁻¹ with a detection limit of 5.6×10⁻⁷ mol l⁻¹. The determination of the lithium ions content in different samples of natural waters samples using the proposed methodology and atomic absorption spectrophotometry are in agreement at the 95% confidence level and within an acceptable range of error.     

Water hyacinth modified carbon paste electrode for simultaneous electrochemical stripping analysis of Cd (II) and Pb (II)

In this study, we demonstrated a highly sensitive electrochemical sensor for the simultaneous detection of Pb (II) and Cd (II) in aqueous solution using carbon paste electrode modified with Eichhornia crassipes powder by square wave anodic stripping voltammetry. The effect of modifier composition, pH, preconcentration time, reduction potential and time, and type of supporting electrolyte on the determination of metal ions were investigated. Pre-concentration on the modified surface was performed at open circuit. The modified electrode exhibited well-defined and separate stripping peaks for Pb (II) and Cd (II). Under optimum experimental conditions, a linear range for both metal ions was from 10 to 5000 μg L^?1 with the detection limits of 4.9 μg L^?1, 2.1 μg L^?1 for Cd(II) and Pb (II), respectively. The modified electrode was found to be sensitive and selective when applied to determine trace amounts of Cd (II) and Pb (II) in natural water samples.     

Copper speciation by competing ligand exchange method using differential pulse anodic stripping voltammetry with ethylenediaminetetraacetic acid (EDTA) as competing ligand

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)-EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)-EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)-fuvic acid and Cu(II)-humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE-ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 10²⁰ and a corresponding very high concentration (above 100 nM) of the ligand.     

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.     

电活化玻碳电极差分脉冲溶出伏安法测定磺胺嘧啶

采用线性循环溶出伏安法和差分脉冲溶出伏安法对磺胺嘧啶在电活化玻碳电极上的电化学行为进行了研究。玻碳电极在PBS溶液中(pH 7.0),用恒电位法在1.7 V阳极氧化400 s,在B-R缓冲溶液中,磺胺嘧啶在1.02V(vs.Ag/AgCl)处有一良好的氧化峰,在0.02～0.25 V/s范围内,其氧化峰电流与扫描速率呈良好线性关系,表明电极过程为受吸附控制的不可逆过程。差分脉冲溶出伏安法的氧化峰电流(Ipa)与磺胺嘧啶浓度1×10-6～1×10-4mol/L范围内呈良好的线性关系(r=0.9977),检出限为8.7×10-7mol/L(S/N=3)。方法已用于分析磺胺嘧啶片剂的分析。     

Comparison of linear scan and differential pulse anodic stripping voltammetry at a thin mercury film glassy carbon electrode

The use of the differential pulse mode in anodic stripping voltammetry with an electrode consisting of a thin mercury film deposited in situ on a glassy carbon support leads to detection limits which are 3–5 times lower than if a simple linear scan is used at the same electrode. If the glassy carbon electrode has a high base current, the improvement in detection limit with differential pulse will be even greater. Differential pulse peak currents, however, are more susceptible to interference by surface-active substances, and undetected adsorption/desorption effects can cause serious errors. Precautions which are necessary to maintain a glassy carbon electrode in good condition are described.     

Square-wave voltammetric stripping analysis of thallium(III) at a poly(4-vinylpyridine)/mercury film electrode

A poly(4-vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square-wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion-exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface-active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.     

Thermal study of Cu(II), Ni(II) and Pd(II) chelates of resacetophenoneoxime

Summary Thermal analysis of resacetophenoneoxime and its chelates of Cu(II), Ni(II) and Pd(II) is carried out. A comparison is made between the thermal stability and the solution stability of chelates and found that they oppose each other. The thermal stability for the chelates studied is PdNi>Cu and the solution stability on the other hand is Pd>Cu>Ni. The results obtained were compared with the data available in the literature for structurally similar oximes. The advantages of the reagent for gravimetric and thermogravimetric analysis of metal ions were discussed.

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Thermochemische Untersuchung der Cu(II)-, Ni(II)- und Pd(II)-Chelate von Resacetophenonoxim

Zusammenfassung Die thermische Stabilität der Chelate und ihre Stabilität in Lösung wurden verglichen und festgestellt, daß diese sich nicht entsprechen. Die erste nimmt ab in der Reihenfolge PdNi>Cu, die zweite in die Reihenfolge Pd>Cu>Ni. Die erhaltenen Ergebnisse wurden denen aus der Literatur für strukturell ähnliche Oxime gegenübergestellt. Die Vorteile des Reagenses für gravimetrische und thermogravimetrische Bestimmungen werden diskutiert.