Determination of thallium in lead salts by differential pulse anodic-stripping voltammetry

The determination of trace levels of thallium in lead and lead salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte without surfactant, lead at concentrations below 0.5mM does not give a peak. When the electrolyte also contains tetrabutylammonium chloride (TBAC) at 0.01 M concentration, lead can be tolerated at concentrations up to 0.05M, while the height of the thallium peak is unaffected. It is thus possible to determine 5nM T1(I) in the presence of 0.05M Pb(II), i.e., Tl at the 1 x 10(-5)% level in lead. The precision of the determination (1-4%) and the recovery are satisfactory. Neither an 800-fold excess ratio of Cu(II) to Tl(I) nor a 10(7)-fold ratio of Bi(III) interferes in the determination. Thallium has been determined in a range of lead salts of various degrees of purity.     

Determination of arsenic in polluted waters by differential pulse anodic-stripping voltammetry

Experimental parameters affecting the analytical response of arsenic in differential pulse anodic-stripping voltammetry (DPASV) have been examined. DPASV offers higher sensitivity than linear-scan anodic-stripping voltammetry for similar analysis times. Both techniques have been applied to the NBS Standard Reference Water (SRM 1643) and some polluted water samples. The results on polluted waters compared favourably with those obtained by graphite-furnace atomic-absorption spectroscopy.     

Determination of thallium in bismuth by differential pulse anodic-stripping voltammetry without preliminary separation

The determination of trace levels of thallium in bismuth and bismuth salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent, in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte in the absence of surfactant, bismuth at concentrations below 10(-4)M does not interfere. When the electrolyte also contains tetrabutylammonium ions at 0.01 M concentration, bismuth can be tolerated at concentrations up 0.05M, and the height of the thallium peak is unaffected. It is thus possible to determine 1 nM Tl(I) in the presence of 0.05M Bi(III), i.e., Tl at the 1 x 10(-6)% level in bismuth. The precision of the determination and the recovery are satisfactory. Neither an 800-fold ratio of Cu(II) nor a 10(7)-fold ratio of Pb(II) to Tl(I) interferes in the determination. Other cations such as Zn(2+), Cd(2+), In(3+), Hg(2+), Fe(3+), Sb(3+) and Sn(4+) in 10(4)-fold molar ratio to Tl(I) have no effect on the determination. Thallium has been determined in bismuth metal and in bismuth nitrate of various degrees of purity.     

Determination of nanomolar concentrations of lead and cadmium by anodic-stripping voltammetry at the silver electrode

Lead and cadmium have been determined by subtractive anodic-stripping voltammetry (SASV) in the square-wave mode at a silver electrode without removal of oxygen. The sensitivities and detection limits for the two metals differ considerably. Detection limits of 0.05 nM for lead and 1 nM for cadmium have been achieved following 90 s electrodeposition. The repeatability of consecutive SASV runs is good (for lead 0.5% at 20 nM for 30 s electrolysis, 5% at 0.3 nM for 60 s electrolysis; for cadmium 2.5% at 20 nM for 30 s electrolysis, 5% at 5 nM for 60 s). Hundreds of runs can be carried out without any pretreatment of the electrode. The high stability is attributed to renewal of the electrode surface that takes place during the electrodeposition step in a two-electrode cell: the silver counter/quasi-reference electrode generates silver ions that codeposit with lead and cadmium at the Ag-RDE, thus ensuring a continuity of the latter. Underpotential deposition (UPD) plays a central role in anodic-stripping voltammetry (ASV). During the deposition step, the adatom coverage of trace elements is in the range of 0.01-1% and no bulk deposition is invoked for metals that exhibit UPD. The UPD properties and, as a result, the ASV signals are strongly affected by the type and concentration of the supporting electrolyte. The effects of Cl⁻, Br⁻, SO₄²⁻ and NO₃⁻ are shown. The analysis of lead and cadmium in natural waters has been performed. Surfactants distort the SASV signal. In order to ensure surfactant-free solutions, the samples were pretreated by wet ashing.     

Determination of chlorpromazine and thioridazine by differential pulse voltammetry in acetonitrile medium

This work describes optimal conditions for the determination of chlorpromazine and thioridazine by DPV, with a detection limit of 4.0 x 10(-7)M (0.16 microg/ml). The well-defined peaks indicate that direct measurement in a medium of 0.03 M perchloric acid in acetonitrile is possible and the use of DPV is advantageous when small amounts are to be determined. The sample procedure for pharmaceutical tablets is simple and fast. The method is useful for control of the quality and purity of phenothiazine drugs. The possibility of using numerical analysis to resolve composite signals of the compounds studied has also been demonstrated.     

Polarographic determination of indium(III) after salting-out extraction of the bromide complex into acetonitrile

A simple and sensitive method has been developed for the polarographic determination of indium(III) after solvent extraction into acetonitrile, salted-out from aqueous solution with sodium bromide. The extracted indium(III)-bromide complex gives a well-defined d.c. wave with E(1 2 ) = -0.69 V vs. SCE. The wave-height is directly proportional to the concentration of indium(III) from 1.6 x 10(-6) to 3.0 x 10(-4)M with respect to the original aqueous solution. In the a.c. polarographic method, a linear calibration curve is obtained for indium(III) over the concentration range from 1.6 x 10(-6) to 1.5 x 10(-5)M, and interference from most foreign ions can be eliminated. In particular, 10.0 mg of Fe(III) and 2.5 mg of Tl(III) are tolerated when 1.0 g of ascorbic acid is added. The lower limit of determination is 8 x 10(-8)M indium(III) by the square-wave polarographic method.     

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 trace impurities in high-purity reagents by mercury thin-film anodic-stripping voltammetry

Summary The use of an amalgamated silver-wire electrode, providing a relatively large rate of film area to volume of mercury, seems to present several advantages over the use of the hanging mercury drop electrode (HMDE) for the determination of trace impurities by anodic-stripping voltammetry (ASV). Peak resolution and sensitivity have both been improved by use of the mercury thin-film electrode (MTFE). Preparation, conservation and treatment of the electrode are simple, requiring brief etching of a silver wire with dilute nitric acid, followed by rinsing, drying and direct amalgamation with mercury. The MTFE is stored in mercury, the excess of which is wiped off before use; it is cleaned by anodic-stripping electrolysis at positive potentials. Under these conditions, ASV produces reproducible peak-heights, with excellent dependence on electrolysis time and concentration of impurities. Samples containing nanogram quantities or less of the impurities of interest, are analysed by a four-step procedure: (1) prolonged pre-electrolysis of the supporting electrolyte,in situ in the voltammetric cell, on an auxiliary MTFE; (2) ASV of the supporting electrolyte on a cleaned MTFE; (3) ASV after the dissolution of the sample; (4) ASV after the addition of standards. The method is suitable for the estimation of traces of Zn(II), Cd(II), Tl(I), Pb(II), Sb(III) and Cu(II) in various high-purity reagents. Most impurities have been adequately determined at the 10^–9–10^–8 M level by the regular procedure, and at the 10^–10–10^–9 M level may be determined if the preconcentration (electrolysis) time and rates of potential sweep are increased. The only disadvantage of the method is that the overvoltage of hydrogen evolution is lower for the MTFE than the HMDE.

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Zusammenfassung Die Verwendung einer amalgamierten Silberdrahtelektrode mit einer im Vergleich zum Quecksilbervolumen großen Oberfläche bietet offenbar verschiedene Vorteile bei der Bestimmung von Spurenbeimengungen durch Anodic-stripping Voltammetry (ASV) gegenüber einem hängenden Quecksilbertropfen (HMDE). Peakauflösung und Empfindlichkeit wurden mit Hilfe der Quecksilberdünnschicht-Elektrode (MTFE) verbessert. Herstellung, Aufbewahrung und Behandlung solcher Elektroden sind einfach; sie erfordern eine kurze Anätzung eines Silberdrahtes mit verd. Salpetersäure, Spülung, Trocknung und Amalgamierung mit Quecksilber. Diese Elektroden werden in Quecksilber aufbewahrt, dessen Überschuß vor der Verwendung weggewischt wird. Sie werden durch Anodic-stripping-Elektrolyse bei positivem Potential gereinigt. Unter diesen Bedingungen gibt ASV reproduzierbare Peakhöhen, die zu der Elektrolysezeit und der Konzentration der Beimengungen in gutem Abhängigkeitsverhältnis stehen. Proben, die Nanogrammengen solcher Beimengungen enthalten, werden nach einem Vierstufenverfahren analysiert: 1. verlängerte Vorelektrolyse des Trägerelektrolyten mittels einer Hilfs-MTFE im Voltammetriegefäß; 2. ASV des Trägerelektrolyten mit einer gereinigten MTFE; 3. ASV nach Auflösung der Probe; 4. ASV nach Zugabe der Standards. Die Methode eignet sich zur Bestimmung von Spuren Zn(II), Cd(II), Tl(I), Pb(II), Sb(III) und Cu(II) in verschiedenen hochreinen Reagenzien. Die meisten dieser Verunreinigungen wurden in der Größenordnung 10^–9 bis 10^–8 M mit Hilfe des regulären Verfahrens bestimmt. In der Größenordnung 10^–10 bis 10^–9 M können sie bei Verlängerung der Anreicherungszeit (elektrolytisch) und Erhöhung des Potentialbereichs bestimmt werden. Der einzige Nachteil des Verfahrens ist, daß die Überspannung zur Wasserstoffentwicklung geringer ist als mit dem hängenden Quecksilbertropfen.

     

Polarographic determination of copper(II) after salting-out extraction as thiocyanate in acetonitrile

Summary A simple and sensitive extraction-polarographic method for the determination of copper(II) by use of acetonitrile as solvent is described. The copper(II) complex formed in aqueous solution can be quantitatively extracted into acetonitrile, in which the complex is reduced to give a polarographic wave withE _1/2–0.58 Vvs. SCE. Linear calibration curves for copper(II) are obtained by the dc, ac and differential pulse polarographic methods. Foreign ions such as Hg(II), Bi, Pb(II), Zn and Ni have no effect even in 20-fold amount relative to copper(II), but a 10-fold ratio of Sn(II) does interfere.

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Zusammenfassung Ein einfaches und empfindliches Verfahren zur Extraktion von Kupfer (II) mit Acetonitril und darauf folgende polarographische Bestimmung wurde beschrieben. Der in wäßriger Lösung entstandene Cu(II)-Komplex läßt sich mit Acetonitril quantitativ extrahieren. Er wird dann reduziert und gibt eine polarographische Welle mit dem Halbwellenpotential E_1/2=–0,58 V gegen eine gesättigte Kalomelelektrode. Lineare Eichkurven für Kupfer(II) ergaben sich mit Gleichstrom-, Wechselstrom- und Differential-Puls-Polarographie. Fremdionen wie Hg(II), Bi, Pb(II), Zn und Ni beeinflussen das Ergebnis auch in 20fachem Überschuß nicht, wohl aber stört Sn(II) in 10facher Menge.

     

Investigation by automated differential pulse anodic-stripping voltammetry of the problem of storage of dilute solutions

The storage of dilute solutions of metal ions before their laboratory analysis presents a difficult problem in the examination of many environmental samples. By utilizing the solution container as an electrochemical cell and employing the method of differential pulse anodic-stripping voltammetry at a hanging mercury drop electrode, it is shown that an automated read-out system in an enclosed environment can be developed for monitoring the solution-container interactions that occur over short or extended periods of time. In the present work, interactions of dilute solutions (1-10 mug/l.) of cadmium(II), lead(II), copper(II), zinc(II), and thallium(I) in glass, polyethylene and Teflon containers have been investigated at various pH values and in different ionic environments. The results demonstrate the importance of factors other than pH.     

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 thallium at subtrace level in rocks and minerals by coupling differential pulse anodic-stripping voltammetry with suitable enrichment methods

Ten international reference samples have been analysed for thallium content by differential pulse anodic-stripping voltammetry. Two separation techniques, solvent extraction and ion-exchange, were employed to preconcentrate the thallium: the results were critically compared to establish which was the better separation technique. The values found were quite satisfactory and confirmed the wide scope for application (not yet fully investigated) of voltammetry in geochemical studies.     

Polarographic determination of uranium(VI) after salting-out extraction as 8-quinolinolate in acetonitrile

Summary Uranium(VI) can be extracted as its 8-quinolinolate into acetonitrile by means of salting-out with ammonium and sodium acetates, respectively; the metal oxinates extracted give a well-defined dc polarogram with E _1/2=–0.80V and a sharp square wave (sw) polarogram with E _p=–0.96V in the extract. The dc wave height and the sw peak current are directly proportional to the uranium(VI) concentration in the range of 6.0×10^–6 to 4.0×10^–4M at pH 6.7–10.0 and 8.0×10^–7 to 2.8×10^–5M at pH 10.5–11.0, respectively. A number of ions do not interfere in the presence of EDTA.

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Polarographische Bestimmung von Uran(VI) nach Aussalz-Extraktion als 8-Hydroxychinolat mit Acetonitril

Zusammenfassung Uran(VI) kann durch Aussalzen mit Ammonium- bzw. Natriumacetat als Oxinat mit Acetonitril extrahiert werden. Das extrahierte Oxinat ergibt ein gut ausgebildetes Gleichstrompolarogramm mit E _1/2=–0,80 V bzw. ein scharfes square-wave-Polarogramm mit E _p=–0,96 V. Die Gleichstrom-Stufenhöhe bzw. der square-wave-Peakstrom sind der U(VI)-Konzentration im Bereich 6,0·10^–6-4,0· 10^–4M (pH 6,7–10,0) bzw. 8,0·10^–7-2,8·10 ^–5M (pH 10,5–11,0) direkt proportional. Durch Zusatz von EDTA kann eine Reihe von Störungen ausgeschaltet werden.

     

Evaluation of differential pulse anodic-stripping voltammetry at a stationary mercury-film electrode with stirred solution

Differential pulse anodic-stripping voltammetry at a stationary mercury-film electrode with the solution stirred during the deposition step has been investigated. The sensitivity achieved by using such a simple set-up is similar to that obtained with a mercury-film rotating disk electrode. The effects of various experimental parameters on the peak current are described. Lead and cadmium were used as test systems, and gave detection limits of around 1 x 10(-10)M with 5-min deposition times.     

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).     

微分脉冲阴极溶出伏安法测定呋喃唑酮

研究了呋喃唑酮在玻碳电极上的伏安行为。在 1mol LHCl底液中 ,用微分脉冲阴极溶出伏安法得到一灵敏的呋喃唑酮还原峰 ,峰电位为 0 .0 38V(vs.Ag AgCl)。峰电流与呋喃唑酮浓度在 8× 1 0 -6～ 1× 1 0 -4 mol L范围内呈线性关系 (r=0 .9984) ,检出限为 8× 1 0 -8mol L。该法已用于片剂与合成血清样品中呋喃唑酮含量的测定     

Determination of cobalt by catalytic-adsorptive differential pulse voltammetry

A novel method is described for the determination of cobalt(II) by differential pulse voltammetry, based on accumulation of a cobalt complex, [CoSCNNO]⁺, on a hanging mercury drop electrode, followed by measurement of the catalytic current of the adsorbed complex. The effects of various experimental parameters on the catalytic current were investigated. The current was found to be linear for 0.3 nM to 100 nM Co, with a detection limit of 70 pM (4.1 ng l⁻¹) and a relative standard deviation of 1.6% for 50 nM Co (n = 25). The developed method showed considerable selectivity against nickel and zinc. A possible mechanism of the reduction process is proposed.     

Determination of ascorbic acid by differential pulse voltammetry

Summary A new approach to the determination of ascorbic acid has been realized with differential pulse voltammetry (DPV) on the carbon paste electrode (CPE). The problems of the reproducibility of the surface of this electrode have been resolved by using always the same surface after its conditioning. The developed method has been applied to the direct determination of vitamin C in pharmaceutical tablets and in different types of fruit juices. Limits of determination are 1.5 ×10^–7 M, 8×10^–7 M and 1×10^–5 M for tablets, dehydrated and liquid juices, respectively.

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Bestimmung von Ascorbinsäure durch Differential-Puls-Voltammetrie

Zusammenfassung Als neues Verfahren zur Ascorbinsäurebestimmung wird die Differential-Puls-Voltammetrie mit Hilfe der Kohlepasteelektrode vorgestellt. Das Problem der Reproduzierbarkeit der Elektrodenoberfläche wurde dadurch gelöst, daß nach Konditionierung immer dieselbe Oberfläche verwendet wurde. Das Verfahren wurde zur Analyse von pharmazeutischen Tabletten und Fruchtsäften angewendet. Die Bestimmungsgrenzen liegen bei 1,5·10^–7 M, 8·10^–7 M und 1·10^–5 M für Tabletten, dehydratisierte bzw. flüssige Säfte.

     

Determination of sulfonamides in swine muscle after salting-out assisted liquid extraction with acetonitrile coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system prior to high-performance liquid chromatography

A salting-out assisted liquid extraction coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system combined with high-performance liquid chromatography with diode-array detection (HPLC–DAD) was developed for the extraction and determination of sulfonamides in solid tissue samples. After the homogenization of the swine muscle with acetonitrile and salt-promoted partitioning, an aliquot of 1 mL of the acetonitrile extract containing a small amount of dichloromethane (250–400 μL) was alkalinized with diethylamine. The clear organic extract obtained by centrifugation was used as a donor phase and then a small amount of water (40–55 μL) could be used as an acceptor phase to back-extract the analytes in the water/acetonitrile/dichloromethane ternary component system. In the back-extraction procedure, after mixing and centrifuging, the sedimented phase would be water and could be withdrawn easily into a microsyringe and directly injected into the HPLC system. Under the optimal conditions, recoveries were determined for swine muscle fortified at 10 ng/g and quantification was achieved by matrix-matched calibration. The calibration curves of five sulfonamides showed linearity with the coefficient of estimation above 0.998. Relative recoveries for the analytes were all from 96.5 to 109.2% with relative standard deviation of 2.7–4.0%. Preconcentration factors ranged from 16.8 to 30.6 for 1 mL of the acetonitrile extract. Limits of detection ranged from 0.2 to 1.0 ng/g.