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 traces of bismuth in copper by anodic stripping voltammetry

Summary Procedures are described for the determination of bismuth impurities in. copper using anodic stripping voltammetry on a hanging mercury drop electrode. Bismuth was previously separated from copper by cation or anion exchange in hydrochloric acid. The method was applied to the analysis of commercially available high purity copper, showing satisfactory sensitivity and accuracy. The detection limit was about 2×10^–9 M bismuth in solution for a pre-electrolysis time of 15 min (–0.5 V vs. Ag/AgCl); this corresponds to 0.004 ppm of bismuth for a 1 g sample and a final volume of 10 ml after separation.

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Bestimmung von Wismutspuren in Kupfer durch anodische Amalgamvoltammetrie

Zusammenfassung Mit hängendem Quecksilbertropfen. Wismut wird vor der Bestimmung durch Kationen oder Anionenaustausch aus salzsaurer Lösung vom Kupfer abgetrennt. Das Verfahren wurde zur Analyse von handelsüblichem hochreinem Kupfer angewendet. Mit einer Vorelektrolysedauer von 15 min (–0,5 V gegen Ag/AgCl) konnten noch 2×10^–9 M Bi bestimmt werden; das entspricht 0,004 ppm Bi für eine 1 g-Probe bei einem Endvolumen von 10 ml nach der Trennung.

     

Determination of traces of antimony and tin in copper by anodic stripping voltammetry

The determination of antimony and tin impurities in copper by anodic stripping voltammetry on a hanging mercury drop electrode is described. Antimony and tin were previously separated from copper by distillation with hydrobromic acid or a mixture of hydrobromic acid and hydrochloric acid. The method was applied to the analysis of various high-purity copper samples, commercially available, showing satisfactory sensitivity and precision. The determination limit was about 1.4· 10^-9M for antimony and 7·10^-10M for tin in solution, for pre-electrolysis times of respectively 15 and 25 min; this corresponds to 0.8 p.p.b. of antimony and 0.3 p.p.b. of tin for a 2-g sample and a final volume of 10 ml after separation.     

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.     

Determination of traces of lead, thallium, and cadmium in zinc salts by means of anodic stripping voltammetry

Summary A method is described by which it is possible to determine traces of lead, thallium, and cadmium in zinc salts by means of anodic stripping voltammetry in a concentration range of about 0.1 to 20 ppm, with a possible error of 10 to 20%. As far as could be investigated, no other elements interfere with the determination.

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Zusammenfassung Eine Methode wird beschrieben zur Bestimmung von Blei, Cadmium und Thallium in Zinksalzen durch anodische Amalgamvoltammetrie. Das Verfahren ist geeignet für Gehalte von etwa 0,1–20 ppm, bei einem möglichen Fehler von 10–20%. Soweit nachgeprüft werden konnte, wird die Bestimmung von keinen anderen Elementen gestört.

     

Determination of traces of copper and silver in tantalum metal by anodic stripping voltammetry

Summary Nanogram quantities of copper and silver are electrodeposited on a glassy carbon electrode from a hydrofluoric-nitric acid solution containing 0.5–1 g of tantalum. The deposit is then anodically removed in 0.1M hydrochloric acid, a current-voltage curve being recorded. The impurities at the parts per billion level in high-purity tantalum metal powder are determined within 3 hours.

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Zusammenfassung Nanogrammengen Kupfer und Silber werden aus flußsaurer, salpetersaurer Lösung von 0,5–1 g Tantal elektrolytisch an einer Elektrode aus glasartigem Kohlenstoff abgeschieden. Während der anodischen Auflösung in Salzsäure wird eine Stromspannungskurve geschrieben. Verunreinigungen in der ppb-Größenordnung in hochreinem Tantalpulver lassen sich so innerhalb 3 Stunden bestimmen.

     

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 copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

Determination of zinc in sea-water by anodic stripping voltammetry

The horizontal distribution of zinc in surface waters from Guanabara Bay has been studied by use of optimized voltammetric techniques and ultraclean working procedures. The non-linearity observed between the peak current for zinc and the electrolysis time, as well as the appearance of a peak at −1.16 V, are discussed. The values found for total zinc in the samples range between 0.3 and 22 μg/l.     

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 traces molybdenum by catalytic adsorptive stripping voltammetry

A reliable and very sensitive procedure for the determination of ultra trace of molybdenum is proposed. Molybdenum was determined by cathodic stripping differential pulse voltammetry based on the adsorption collection of the Mo(VI)-Tiron complex on a hanging mercury drop electrode (HMDE). The variation of peak current with pH, concentration of Tiron and chlorate, plus several instrumental parameters such as accumulation time, accumulation potential and scan rate, were optimized. Under optimized condition, the relationship between the peak current and molybdenum concentration is linear in the range of 0.010-21.0 ng ml⁻¹. The limit of detection was found to be 0.006 ng ml⁻¹. The relative standard deviation for 10 replicates determination of 0.6 and 10 ng ml⁻¹ Mo(VI) is equal to 1.3 and 0.9%, respectively. The method was applied to the determination of molybdenum in river water, tap water, well water, plant foodstuff samples such as cucumber, tomato, carrot, and certified steel reference materials.     

Determination of thallium in natural waters by anodic stripping voltammetry

Thallium was determined in natural waters by anodic stripping voltammetry at a hanging mercury drop electrode, in acetate buffer pH 4.6+EDTA, after preconcentration and separation on an anion exhange resin. For Pacific Ocean surface waters a mean value of 13.0±1.4 ng Tl l^?1 was found, while for freshwater samples the value was 3.7±1.0 ng Tl l^?1. Thermodynamic considerations of thallium speciation predict that both in seawater and freshwater thallium exists primarily in the trivalent state. This was confirmed by experiment.     

Determination of thallium in soils by flow-injection-differential pulse anodic stripping voltammetry

A relatively simple and quick method for the determination of thallium in soils is described. The method does not require any separation prior to determination. Total decomposition of the sample was performed in a teflon bomb. The interferences of iron, aluminum and manganese were removed by media exchange performed in a flow-injection measuring system, and the other interferences were removed by the use of the base electrolyte consisting of 0.15M EDTA and 0.1M ascorbic acid. The contents of thallium in the examined samples of soil were between 100 and 350 ppb.     

Determination of copper and lead in schist by anodic stripping voltammetry

Samples were decomposed in HClO₄/HF mixture in a Teflon beaker to avoid electrochemical interference from platinum ions. The residue remaining after evaporation to dryness was taken up in nitric acid and examined by anodic stripping voltammetry. Both the hanging mercury drop electrode and the rotating glassy carbon electrode, mercury-plated in situ, were used with success. Copper at 120 ppm and lead at 40 ppm were determined with a relative standard deviation of 6%. The schist was the Nordic reference sample ASK-2.     

Determination of sub-micromolar amounts of sulfide by standard free anodic stripping voltammetry and anodic stripping voltammetric titration

A novel electrochemical methods namely standard free anodic stripping voltammetry and anodic stripping voltammetric titration are proposed for determination of dissolved sulfide concentration. 2Ag⁺ + S²⁻ → Ag₂S reaction is used to provide the information. The anodic stripping voltammetric response of unreacted silver-ions at the glassy carbon electrode is used as analytical signal. Results reliability and accuracy are confirmed by analysis of model solutions, spiked natural and tap waters and recovery study, with a recovery of 100 ± 5% (n = 7) obtained. The approaches show the detection limit (3σ_blank) of 2-5 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of 2-5% for repeated measurements.     

Trace analysis by anodic stripping voltammetry

Summary An anodic stripping voltammetric method for the determination of zinc in silicates is described and discussed. The method is sensitive and is not affected by interferences resulting from varying sample composition.

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Zusammenfassung Ein Verfahren zur Bestimmung von Zink in Silicaten mit Hilfe der anodischen Amalgamvoltammetrie wird beschrieben und diskutiert. Das Verfahren ist empfindlich und wird durch verschiedenartige Zusammensetzung der Probe nicht beeinflußt.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.

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This work was performed under the sponsorship of the U.S.National Bureau of Standards. Reproduction of this article, with the customary credit to the source, is permitted.     

Determination of thallium and lead in cadmium salts by anodic stripping voltammetry with addition of surfactants to suppress the cadmium peaks

Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10^?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10^?2M and 10^?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium.