Indirect determination of the sum of chelons in drinking- and ground-waters by anodic stripping voltammetry

The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions. Received: 9 September 1996 / Revised: 2 December 1996 / Accepted: 11 January 1997     

Indirect trace determination of NTA in natural waters by differential pulse anodic stripping voltammetry

Summary Bismuth(III) is added to the water sample in excess to NTA and EDTA to form inert stable complexes with them at pH 2. The uncomplexed Bi(III) is then deposited into a hanging mercury drop electrode at a potential of –0.15 V vs. SCE and subsequently stripped anodically in the differential pulse mode. The peak current of uncomplexed Bi(III) is recorded. By a second deposition at –0.35 V vs. SCE Bi(III) from Bi³⁺ and Bi-NTA is deposited. The concentrations of NTA and EDTA in the sample are determined from the concentration of added Bi(III) and the voltammetrically determined Bi(III) at these two potentials by the standard addition method. Cd, Cu, Pb, and Zn do not interfere. Fe(III) has to be reduced by ascorbic acid or hydroxylamine before the determination. Cu(II) in concentrations larger than 40 g/l has to be removed by preelectrolysis. In samples with chloride contents above 0.05 M the stripping step has to be performed after medium exchange to a perchloric acid solution of pH 2. For a deposition time of 2 min the determination limit is approximately 0.2 g/l NTA and 0.1 g/l EDTA. The relative standard deviation for NTA concentrations at 2 or 10 g/l lies at 10 or 1.3%, respectively. Good accuracy is established by finding within 2% the levels adjusted when water samples are spiked with a standard solutions of NTA or EDTA.

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Indirekte Spurenbestimmung von NTA in natürlichen Wässern durch differentielle Pulsinversvoltammetrie

Zusammenfassung Bismuth(III) wird zur Wasserprobe in Überschuß zur NTA- und EDTA-Konzentration bei pH 2 zugegeben, wobei stabile inerte Komplexe gebildet werden. Nicht komplexiertes Bi(III) wird an der hängenden Quecksilbertropfenelektrode beim Potential –0,15 V (SKE) kathodisch als Amalgam abgeschieden und dann anodisch wieder gelöst. Dabei wird im differentiellen Pulsmodus der Bi(III)-peak registriert. Durch die zweite kathodische Abscheidung beim Potential –0,35 V (SKE) wird Bi(III) aus unkomplexiertem Bi³⁺ und dem BiNTA-Komplex abgeschieden. Die Konzentrationen von NTA und EDTA in der Probe werden aus den voltammetrisch bestimmten Bi(III)-Konzentrationen bei den zwei angegebenen Potentialen und der zugegebenen Konzentration von Bi(III) mit der Standard-Additions-Methode bestimmt. Die Spurenmetalle Cd, Cu, Pb und Zn stören die Bestimmung nicht. Fe(III) muß vor der Bestimmung mit Ascorbinsäure reduziert werden, Cu in der Konzentration von mehr als 40 g/l muß durch Vorelektrolyse entfernt werden. Wenn die Probe mehr als 0.05 M Chlorid enthält, muß der Strippingvorgang nach Elektrolytwechsel in einer Perchlorsäurelösung bei pH 2 durchgeführt werden. Für eine Anreicherungszeit von 2 min liegt die Bestimmungsgrenze bei 0,2 g/l NTA und 0,1 g/l EDTA. Die relative Standardabweichung beträgt bei einer Konzentration von 2, bzw. 10 g/l NTA 10 bzw. 1,3%. Die Richtigkeit ist gut, was aus der Wiederfindungsrate von 2% der zur Probe zugegebenen Lösung des NTA- oder EDTA-Standards hervorgeht.

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday

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On leave from the University of Thessaloniki, Greece     

The determination of gold by anodic stripping voltammetry

A method is described for the routine determination of gold as its chloride or cyanide complex by anodic stripping voltammetry at a glassy carbon electrode coupled to a microprocessor-controlled voltammeter. The preferred supporting electrolyte is 0.1 M HCl/0.32 M HNO₃, with plating at ?200 mV or ?1200 mV (vs. Ag/AgCl). The stripping peak potentials range from 830 to 1150 mV (vs. Ag/AgCl) depending on concentration and plating time. Precision (percent relative standard deviation) is better than 5 % for a range of concentrations between 5 μg l^?1 and 1000 μg l^?1. The detection limit is about 5 μg l^?1 for a 5-min plating period. Interferences from Cu, Hg, Ag and other electroactive species are overcome by preliminary extraction with diethyl ether.     

Trace-metal determination by second-harmonic alternating-current anodic stripping voltammetry

Second-harmonic alternating-current voltammetry can be used for the sequential determination of two electroactive species having very similar half-wave potentials (deltaE(1 2 ) < 50 mV). Since the concentrations of such metals in samples of special interest are often at trace levels, for their determination second-harmonic a.c. voltammetry (extremely selective but not sufficiently sensitive) can usefully be combined with the anodic stripping method, which has a very high analytical sensitivity. The determination of tin and lead as well as of indium and cadmium in 1M hydrochloric acid is described. The half-wave potentials are only 35 and 45 mV apart, respectively, for these systems. A three-electrode cell was used with a long-lasting sessile-drop mercury electrode as the working electrode, with a drop-time of 240-300 sec. The detection limit was found to be 10(-8)M for all four elements studied. The precision expressed as the relative standard deviation was 2-3% and the relative error was 1-2%.     

Indirect determination of surfactants by adsorptive stripping voltammetry

The effect of some anionic, cationic and nonionic surface-active substances on the suppression of adsorptive accumulation of the bis(dimethylglyoximato)nickel(II) complex, Ni(DMG)₂, is described. Competitive adsorption of surfactants can be used to determine surfactants commonly used in commercial detergents. Triton X-100 shows the most pronounced effect on the peak height. The shape of the calibration curve depends on the concentration and on the adsorption potential. Highest sensitivity is obtained when equilibrium between Ni(DMG)² in solution and on the electrode surface is attained rapidly. Under these conditins, the detection limit is 1 μ 1^?1 Triton X-100. Calibrations are linear over 1–2 orders of magnitude.     

Simultaneous determination of mercury and arsenic by anodic stripping voltammetry

An electrochemical method for the simultaneous determinations of Hg^II concentration and total As^III and As^V concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of As^V to As^III, or oxidation of As^III to As^V before stripping analysis takes place. Also, the method for the simultaneous determination of Hg^II concentration and As^III concentration is described. Measurements were performed in 0.1 M HCl using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the Hg^II and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of As^V to As^III or oxidation of As^III to As^V decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.     

The determination of silver in ores by anodic stripping voltammetry

Stripping voltammetry at a rotating glassy carbon electrode is proposed for the determination of silver in ores. The ores or concentrates are dissolved in suitable acid mixtures, and silver is separated either by extraction with dithizone in carbon tetrachloride, or by adsorption on silica from ammoniacal buffered solution and subsequent elution with 0.1 M nitric acid. The results obtained with stationary and rotating glassy carbon electrodes are discussed. Stripping voltammetry and fire assay give results in reasonably good agreement.     

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.      

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10⁻⁸ to 1×10⁻⁶ mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10^–8 to 1×10^–6 mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Direct determination of selenium in whole blood by anodic stripping voltammetry

Trace quantities of selenium can be determined in the presence of iron, copper and lead using anodic stripping voltammetry, depositing at –0.60 V in 0.1M HClO₄ and stripping in the anodic direction. Two separate peaks are observed at –0.25 V and –0.10 V belonging to copper and selenium, respectively. Sometimes one peak may be observed for both copper and selenium. In this case one more stripping (without deposition) must be done to obtain separate peaks. After standard addition, two strippings have to be done also. With this proposed method, 10^–7 M selenium could be determined as (1.09±0.03) × 10^–7 M with a 90% confidence interval in blood samples without any separation.Presented at Xth National Chemistry Congress, Bursa, Turkey, September 19–21, 1994     

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.     

Interferences in the determination of copper in natural waters by anodic stripping voltammetry

Copper(I)-binding anions such as cyanide and thiocyanate, and polysaccharides, when present in non-saline waters are shown to produce an additional, more anodic wave during the determination of copper by stripping voltammetry. The origins of this wave and potential interferences in determinations of copper and copper-complexing capacities are discussed. The effect of inadequate oxygen removal is reported.     

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.     

The determination of copper in silicon by anodic stripping and differential pulse voltammetry

A critical comparison of the application of differential pulse voltammetry and anodic stripping voltammetry to the determination of micro amounts of copper in silicon is described. The anodic stripping technique offers advantages when a dropping mercury capillary with a long drop time is used. The method recommended allows the determination of copper in silicon with a precision of ± 5 %; the limit of determination is about 1μg g^-1. Calibration graphs are linear in the range 0–0.2 μg Cu ml^-1. Methods for the dissolution of silicon are also compared.     

Direct determination of bismuth and antimony in sea water by anodic stripping voltammetry

A method based on anodic stripping voltammetry at the mercury-coated graphite electrode has been developed for the direct determination of bismuth and antimony at their natural levels in sea water. Bismuth plated at -0.4 V from sea water made 1 M in hydrochloric acid gives a stripping peak proportional to concentration at -0.2 V without interference from antimony or other metals normally present. Antimony may be plated from sea water made 4 M in hydrochloric acid and gives a stripping peak at -0.2 V proportional to the sum of bismuth and antimony. By use of the standard addition technique, satisfactory results were obtained for sea water samples with concentration ranges of 0.02–0.09 μg kg^?1 for bismuth and 0.2–0.5 μg kg^?1 for antimony.     

Rapid determination of trace concentrations of lead in gasoline by anodic stripping voltammetry

Anodic stripping voltammetry can be used for the determination of g/l concentrations of lead in gasoline. A gasoline sample is extracted with iodine monochloride reagent solution. An aliquot of the aqueous phase is pipetted into the measuring cell of the voltammeter. The ease of this method makes it a good alternative to atomic absorption spectrophotometry.     

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.