Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

Cathodic stripping voltammetric analysis of arsenic species in environmental water samples

A simple, fast and sensitive arsenic speciation method has been developed for environmental water analysis by using differential pulse cathodic stripping voltammetry (CSV) performed on a hanging mercury drop electrode (HMDE). Electroactive As(III) is determined by direct CSV analysis. As(V) is converted to As(III) species first and is subsequently quantified by the concentration difference between total inorganic arsenic and As(III). A new batch-mode As(V) reduction procedure by l-cysteine was developed in this study. The optimized parameters for quantitative As(V) reduction include treatment with 20 mM l-cysteine and 0.03 M HCl for 6 min at 70 °C. Organic arsenic, including monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), can be decomposed to As(V) through UV photooxidation with peroxydisulfate and quantified through subtracting total inorganic arsenic from the total arsenic. At optimum condition, the detection limits for As(III), As(V), and organic arsenic (MMA and DMA) were all 0.3 μg/L and with the linear range from 2.5 to 190 μg/L. Interference from ions common in natural water (Mn, Fe, Cr, Cd, Ca, Zn, Mg, and phosphate) is minimal. The method was validated by analyzing the NIST 1640 natural water standard reference material and by recovery tests on spiked tap water and groundwater. When applied to on-site analysis of sediment pore water and stream water, the CSV results agree well with those obtained by inductively coupled plasma–mass spectrometry (ICP–MS) and graphite furnace atomic absorption spectrometry (GFAAS) methods.     

Sensitive electrochemical detection of arsenic (III) using gold nanoparticle modified carbon nanotubes via anodic stripping voltammetry

Gold nanoparticles were deposited electrolessly on multiwalled carbon nanotubes (CNTs) via in situ reduction of HAuCl₄ by NaBH₄. The resulting gold covered nanotubes were immobilised onto the surface of a glassy carbon electrode via evaporation of a suspension in chloroform. Anodic stripping voltammetry was performed with the modified electrode in As(III) solutions. A limit of detection (LOD based on 3σ) of 0.1 μg L⁻¹ was obtained but more importantly a sensitivity of 1985 μA μM⁻¹ was obtained with square wave voltammetry (SWV) in an optimised system with a deposition time of 120 s. These values, particularly the high sensitivity compare favourably with previously reported methods in the area of electrochemical arsenic detection.     

On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l⁻¹ HNO₃. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO₄ (50.0 μmol l⁻¹). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h⁻¹ and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l⁻¹ for As(V) and 0.10 μg l⁻¹ for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l⁻¹ level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l⁻¹ with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.     

Selective determination of arsenic(III) and arsenic(V) with ammonium pyrrolidinedithiocarbamate, sodium diethyldithiocarbamate and dithizone by means of flameless atomic-absorption spectrophotometry with a carbon-tube atomizer

The extraction behaviour of arsenic(III) and arsenic(V) with ammonium pyrrolidinedithiocarbamate, sodium diethyldithiocarbamate and dithizone in organic solvents has been investigated by means of nameless atomic-absorption spectrophotometry with a carbon-tube atomizer. The selective extraction of arsenic(III) and differential determination of arsenic(III) and arsenic(V) have been developed. With ammonium pyrrolidinedithiocarbamate and methyl isobutyl ketone or nitrobenzene, when the aqueous phase/solvent volume ratio is 5 and the injection volume in the carbon tube is 20 μl, the sensitivities for 1% absorption are 0.4 and 0.5 part per milliard of arsenic, respectively. The relative standard deviations are ca. 3%. Interference by many metal ions can be prevented by masking with EDTA. The proposed methods are applied satisfactorily for determination of As(III) and As(V) in various types of water.     

Differential pulse polarographic determination of inorganic and organic arsenic in natural waters

Summary As(III), As(V) and organic arsenic in water are determined by differential pulse polarography. As (III) is directly determined in 2M HCl as supporting electrolyte. Total inorganic arsenic [As (III) + As(V)] is measured after reduction of electro-inactive As(V) with sodium sulphite. Total arsenic is determined after oxidative treatment of the water residue with potassium permanganate and magnesium nitrate, and reduction of arsenic with sodium sulphite. Organic arsenic is evaluated by difference. The efficiency of the whole procedure is 78–80% and its detection limit is 1g/l. The relative standard deviation is better than ±1.5% at 50g/l. Interferences due to heavy metals are overcome by removing them by anionexchange or pre-electrolysis with a mercury cathode.

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Differential-puls-polarograpbische Bestimmung von anorganischem und organischem Arsen in natürlichen Wässern

Zusammenfassung As (III), As(V) und organisches Arsen in Wässern wurden differentialpuls-polarographisch bestimmt. As (III) wurde direkt in 2 M HCl als Trägerelektrolyt bestimmt. Das anorganische Gesamtarsen [As(III) und As(V)] wurde nach Reduktion des elektro-inaktiven As(V) mit Natriumsulfit gemessen. Nach der oxydativen Behandlung des Wasserrückstandes mit KMnO₄ und Magnesiumnitrat und nach Reduktion des Arsens mit Natriumsulfit wurde das Gesamtarsen bestimmt, und das organisch gebundene Arsen durch Differenzbildung ermittelt. Die Ausbeute des gesamten Verfahrens beträgt 78–80%, seine Erfassungsgrenze 1g/l Die relative Standardabweichung ist besser als ±1,5% bei 50g/l. Störungen durch Schwermetalle werden entweder durch deren Entfernung mittels Anionen-austauscher oder durch vorhergehende Elektrolyse mit einer Quecksilberelektrode beseitigt.

     

Potentiometric microdetermination of arsenic with an iodide-selective electrode

Summary Micro amounts of arsenic(III) can be determined potentiometrically by titration with cerium(IV) sulphate at pH 2 with iodide as catalyst. An iodide-selective electrode is used to follow changes in the iodide concentration during the titration. Arsenic(III) at a concentration of 0.1g/ml can be determined with a relative standard deviation of about 5%. Total arsenic can also be determined with an error of 10–12%, the arsenic(V) being reduced with sodium bisulphite to arsenic(III). Direct determination of not less than 100 ng/ml of arsenic(III) in the presence of an unspecified amount of arsenic(V) and up to a fiftyfold ratio of iron(II), sulphide, thiosulphate, tin(II) and antimony(III) is possible.

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Potentiometrische Mikrobestimmung von Arsen mit einer jodidspezifischen Elektrode

Zusammenfassung Mikromengen Arsen(III) können potentiometrisch mit Cer(IV)-sulfat bei pH 2 mit Jodid als Katalysator bestimmt werden. Eine jodid-spezifische Elektrode dient zur Kontrolle der Jodid-Konzentrations-Veränderungen während der Titration. Arsen(III) Iäßt sich in einer Konzentration von 0,1g/ml mit einer rel. Standardabweichung von 5% bestimmen. Das Gesamt-Arsen kann ebenfalls mit einem Fehler von 10–12% bestimmt werden, nachdem Arsen(V) mit Natriumsulfit zu Arsen(III) reduziert wurde. Die unmittelbare Bestimmung von wenigstens 100 ng/ml Arsen(III) in Gegenwart einer unbestimmten Menge von Arsen(V) und bis zu einer 50-fachen Menge Fe(II), Sulfid, Thiosulfat, Sn(II) und Antimon (III) ist möglich.

     

Study and optimization of the resazurin/diaphorase system

This study describes the resazurin/diaphorase system and its use in a kinetic assay for the determination of dehydrogenase activity. This has increased the sensitivity (limit of detection is 2 × 10⁻⁵ U/ml) and produced calibration curves which have an extended linear range and better separation of points. The specific activity of diaphorase when resazurin (6.7 μM) is used as a substrate is only about 2 × 10⁻³ that when 2,6-dichlorophenol-indophenol (DCPIP)² is used as a substrate. The specific activity of diaphorase can be increased by using higher concentrations of resazurin. The concentration chosen is influenced by the size of fluorometric cuvette used. In a 3.0-ml cuvette, concentrations above 13.4 μM result in lower signals due to the quenching of the fluorescence by resazurin. In a 1.0-ml cuvette, the quenching effect is less severe and a higher concentration (34 μM) of resazurin can be used. Diaphorase activity is first order in the concentration range up to 34 μM of resazurin, and the K_m could not be calculated from the range tested. The K_m of diaphorase with respect to NADPH is dependent on the concentration of resazurin used. It is 0.78 (± 0.04) and 1.31 (± 0.04) μM at resazurin concentrations of 6.7 and 34 μM, respectively.     

Differential pulse voltammetric determination of arsenic(III,V) and antimony (III,V) in glasses

Summary Analytical methods based on differential pulse voltammetry (DPV) have been described for the determination of total As, As(III), As(V), total Sb and Sb(III) as trace to minor constituents in complex glasses. For total As, the sample is decomposed with HF-H₂SO₄-KMnO₄. The As(V) is chemically reduced to As (III) by hypophosphite and a DPV scan is carried out at the dropping mercury electrode from –0.2 to –0.7 Vvs. SCE (E _p –0.41V). As(V) is determined by decomposing the sample in HF-H₂SO₄ and volatilizing the As(III) as AsF₃. The chemical reduction of As(V) and the DPV scan are then applied. If the glass can be decomposed with cold HF, the As(III) present in the glass can be determined by applying the DPV scan after cold sample-dissolution. For Sb(III), the sample is decomposed with HF-H₂SO₄, diluted, and adjusted to 1M in HCl. A DPV scan is conducted from –0.03 to –0.5 V (E _p –0.15 V). Sb(V) is not reduced in the 1M HCl supporting electrolyte. Total Sb is determined by using an aliquot of the sample solution adjusted to 6M in HCl. The DPV sweep is carried out from –0.5 to –0.1 V [E _p for Sb(V) and Sb(III) is –0.30 V]. The methods have been applied to a wide range of glass compositions and the results compared with values obtained by spectrophotometry and coulometric titration.

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Bestimmung von Arsen(III, V) und Antimon(III, V) in Gläsern mit Hilfe der Differential-Puls-Voltammetrie

Zusammenfassung Analytische Methoden auf der Grundlage der Differential-Puls-Voltammetrie (DPV) für die Bestimmung des gesamten Arsens, As(III), As(V), des gesamten Antimons und Sb(III) als Spuren in komplexen Gläsern wurden beschrieben. Zwecks Bestimmung des Gesamt-As wird die Probe mit Flußsäure +Schwefelsäure + Permanganat aufgeschlossen. As(V) wird mit Hypophosphit reduziert und die DPV wird an einer Quecksilber-Tropfelektrode zwischen –0,2 und –0,7V gegen eine ges. Kalomelelektrode (E _p =–0,41V) durchgeführt. Zur Bestimmung von As(V) wird die Probe mit HF-H₂SO₄ unter Verflüchtigung des As(III) als AsF₃ aufgeschlossen. Dann erfolgt die Reduktion des As(V) und die DPV. Wenn sich das Glas mit kalter HF lösen läßt, wird anwesendes As(III) mittels DPV in dieser Lösung bestimmt. Zur Bestimmung des Sb(III) wird die Probe mit HF-H₂SO₄ zersetzt, verdünnt und bis zur 1-Molarität mit HCl versetzt. Dann wird mit DPV zwischen –0,03 und –0,5V gemessen (E _p =–0,15V). Sb(V) wird in 1M salzsaurer Lösung nicht reduziert. Das Gesamt-Sb wird in einem Aliquot der Probelösung bestimmt, das dazu mit HCl bis zur 6fachen Molarität versetzt wird. Der DPV-Bereich wird von –0,5 bis –0,1 V ausgenützt (E _p f:ur Sb(V) und Sb(III) ist –0,30 V). Das Verfahren wurde für Gläser verschiedenster Zusammensetzung angewendet. Die Ergebnisse wurden mit den Resultaten der Spektrophotometrie und der coulometrischen Titration verglichen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Spectrophotometric determination of molybdenum by extraction of its thiosulphate complex

A simple and rapid spectrophotometric determination of molybdenum is described. The molybdenum thiosulphate complex is extracted into isoamyl alcohol from 1·0–1·5M hydrochloric acid containing 36–40 mg of Na₂S₂O₃·5H₂O per ml. The absorbance at λ_max = 475 nm obeys Beer's law over the range 0–32 μg of Mo per ml of solvent phase. Up to 5 mg/ml of Ti(IV), V(V), Cr(VI), Fe(III), Co(II), Ni(II), U(VI), W(VI), Sb(III), 1 mg/ml of Cu(II), Sn(II), Bi(V) and 10 μg/ml of Pt(IV) and Pd(II) do not interfere. Large amounts of complexing agents interfere. The method has been applied to analysis of synthetic and industrial samples.     

Cacotheline as an oxidimetric reagent. Determination of Sn(II), Cu(I), Ti(III), Fe(II), V(II) and V(III)

Summary Sn(II), Ti(III), Cu(I), Fe(II), V(III) and V(II) can be titrated potentiometrically with cacotheline in 1–4M hydrochloric acid, 0.5–2M hydrochloric acid, 0.5–1.5M sulphuric acid in presence of 4 ml of 10% EDTA solution in a total volume of 50 ml, 9–10M phosphoric acid, 4–8M acetic acid and 3–8M acetic acid respectively. Cacotheline can be used for the assay of tin plate and solder. The cacotheline undergoes a 2-electron reduction reaction. A cacotheline solution (0.005M) in 0.02M hydrochloric acid is fairly stable for several months. The conditional redox potentials of cacotheline have been determined in sulphuric, phosphoric and acetic acid medium.

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Kakothelin als oxydimetriscbes Reagens. Bestimmung von Sn(II), Cu(I), Ti(III), Fe(II), V(II) und V(III)

Zusammenfassung In 1–4M Salzsäure, in 0,5–2M Salzsäure, 0,5–1,5M Schwefelsäure in Gegenwart von 4 ml 10%iger EDTA-Lösung in einem Gesamtvolumen von 50 ml, in 9–10M Phosphorsäure, in 4–8M Essigsäure bzw. in 3–8M Essigsäure kann man die genannten Kationen potentiometrisch mit Kakothelin titrieren. Dieses eignet sich auch für die Untersuchung von Lötzinn. Kakothelin erleidet dabei eine 2-Elektronen-Reduktions-Reaktion. Seine 0,005M Lösung in 0,02M Salzsäure ist einige Monate beständig. Sein Redoxpotential in Schwefelsäure, Phosphorsäure bzw. Essigsäure wurde bestimmt.

     

Determination of inorganic arsenic in white fish using microwave-assisted alkaline alcoholic sample dissolution and HPLC-ICP-MS

An analytical method for the determination of inorganic arsenic in fish samples using HPLC-ICP-MS has been developed. The fresh homogenised sample was subjected to microwave-assisted dissolution by sodium hydroxide in ethanol, which dissolved the sample and quantitatively oxidised arsenite (As(III)) to arsenate (As(V)). This allowed for the determination of inorganic arsenic as a single species, i.e. As(V), by anion-exchange HPLC-ICP-MS. The completeness of the oxidation was verified by recovery of As(V) which was added to the samples as As(III) prior to the dissolution procedure. The full recovery of As(V) at 104±7% (n=5) indicated good analytical accuracy. The uncertified inorganic arsenic content in the certified reference material TORT-2 was 0.186±0.014 ng g^–1 (n=6). The method was employed for the determination of total arsenic and inorganic arsenic in 60 fish samples including salmon from fresh and saline waters and in plaice. The majority of the results for inorganic arsenic were lower than the LOD of 3 ng g^–1, which corresponded to less than one per thousand of the total arsenic content in the fish samples. For mackerel, however, the recovery of As(III) was incomplete and the method was not suited for this fat-rich fish.     

Evaluation of a chloramine-T-selective electrode for catalytic titration of silver and mercury(II) based on iodide-catalyzed chloramine-T reactions

Semiautomatic methods are described for the catalytic titrimetric determination of microamounts of silver and mercury(II) using a chloramine-T-selective electrode as monitor. The methods are based on the inhibitory effect of Ag(I) and Hg(II) on the iodide-catalyzed chloramine-T-arsenite and chloramine-T-H₂O₂ reactions. Microamounts of silver in the range 0.2–200 μg (1 × 10⁻⁷−1 × 10⁻⁴ M) and of mercury(II) in the range 0.1–200 μg (2.5 × 10⁻⁸−5 × 10⁻⁵ M) were determined using the chloramine-T-As(III) indicator reaction. Mercury(II) in the range 4–2000 μg (1 × 10⁻⁶−5 × 10⁻⁴ M) was also determined using the chloramine-T-H₂O₂ indicator reaction. The accuracy and precision were in the range 0.1–1%.     

Protection by methylated urates of oxyhemoglobin oxidation induced by sodium nitrite

When 60 μM sheep oxyhemoglobin was treated with 1.2 mM sodium nitrite, the oxyhemoglobin was completely converted to methemoglobin in 7 min. The addition of increasing concentrations of uric acid (1–10 μM) resulted in a decrease in the rate of methemoglobin formation; at 10 μM, uric acid completely protected the oxyhemoglobin. At a concentration of 5 μM, uric acid and all of the mono- and dimethylurates, with the exception of 3,9-dimethyluric acid, protected oxyhemoglobin from oxidation to methemoglobin by 1.2 mM sodium nitrite; 1,3,9-trimethyl-, 3,7,9-trimethyl-, and 1,3,7,9-tetramethyluric acid did not protect oxyhemoglobin. It was concluded that the hydrogens at nitrogens 3 and 9 of uric acid are necessary for it to prevent the oxidation of oxyhemoglobin by sodium nitrite.     

Determination of As(III) and As(V) ions by chemiluminescence method

A new chemiluminescence (CL) method for the selective determination of As(III) and As(V) ions in aqueous solution has been studied using a FIA system. The method is based on the increased CL intensity with the addition of As(V) ion into a solution of lucigenin and hydrogen peroxide. The addition of As(III) ion into the solution did not change the CL intensity. Total concentration of As ions was determined after pre-oxidation of As(III) to As(V) with hydrogen peroxide in basic solution. The As(III) content was estimated by subtracting the content of As(V) ion from total As concentration. The effects of concentrations of KOH and H₂O₂, and flow rates of reagents on CL intensity have been investigated. The calibration curve for As(V) ion was linear over the range from 1.0×10^-2 to 10 μg/g, the coefficient of correlation was 0.997 and the detection limit was 5.0×10^-3 μg/g under the optimal experimental conditions.     

Study of the stoichiometry and the kinetics of the Jaffé reaction with a picrate ion-selective electrode

Potentiometric studies with the picrate ion-selective electrode indicate that the species formed as the product of reaction between alkaline picrate and creatinine in the Jaffé reaction is a 1:1 complex. Kinetic studies indicate that the forward reaction is first order with respect to picrate, creatinine, and hydroxide concentration. The second-order rate constant k was found to be in the range 9.1–10.4 M⁻² sec⁻¹ at 27 °C and μ = 1.00, with creatinine or picrate in excess, k increases with increasing μ and temperature. An activation energy of 10.1 kcal/mol was calculated for the Jaffé reaction, with creatinine in excess.     

Inorganic arsenic speciation in various water samples with GFAAS using coprecipitation

A simple, economic and sensitive method for selective determination of As(III) and As(V) in water samples is described. The method is based on selective coprecipitation of As(III) with Ce(IV) hydroxide in presence of an ammonia/ammonium buffer at pH 9. The coprecipitant was collected on a 0.45 µm membrane filter, dissolved with 0.5 mL of conc. nitric acid and the solution was completed to 2 or 5 mL with distilled water. As(III) in the final solutions was determined by graphite furnace atomic absorption spectrometry (GFAAS). Under the working condition, As(V) was not coprecipitated. Total inorganic arsenic was determined after the reduction of As(V) to As(III) with NaI. The concentration of As(V) was calculated by the difference of the concentrations obtained by the above determinations. Both the determination of arsenic with GF-AAS in presence of cerium and the coprecipitation of arsenic with Ce(IV) hydroxide were optimised. The suitability of the method for determining inorganic arsenic species was checked by analysis of water samples spiked with 4–20 µg L^?1 each of As(III) and As(V). The preconcentration factor was found to be 75 with quantitative recovery (≥95%). The accuracy of the present method was controlled with a reference method based on TXRF. The relative error was under 5%. The relative standard deviations for the replicate analysis ( n?=?5) ranged from 4.3 to 8.0% for both As(III) and As(V) in the water samples. The limit of detection (3σ) for both As (III) and As(V) were 0.05 µg L^?1. The proposed method produced satisfactory results for the analysis of inorganic arsenic species in drinking water, wastewater and hot spring water samples.     

Tetrachloroferrate(III)-selective liquid membrane electrode based on crystal violet

An extract of crystal violet-tetrachloroferrate(III) in nitrobenzene was used to prepare a tetrachloroferrate(III)-selective liquid membrane electrode with a poly(vinyl chloride) support. The optimal conditions to determine 2.5 × 10^–5 – 5.0 × 10^–2 M iron(III) as tetrachloroferrate(III) (anionic slope 56 mV/decade, detection limit 7.9 × 10^–6 M) were found to be 4.0–5.5.M total chloride in 0.75–1.5M hydrochloric acid. The electrode was reliably applied to determine iron in human blood, haematite and mineralized vitamin syrup by direct potentiometry, standard and sample additions as well as standard subtraction techniques.     

Polarographie in 1,2-Propandiolcarbonat, 3. Mitt.: Verbindungen von Titan,Vanadin und Chrom

Zusammenfassung Titan(III)chlorid, Titan (IV)oxyperchlorat, Vanadin(III)chlorid, Vanadin(IV)oxyperchlorat, Chrom(III)chlorid und Chrom(III)perchlorat wurden in 1,2-Propandiolcarbonat polarographisch untersucht; die Art der Grenzströme, die Diffusionsstromkonstanten, die Diffusionskoeffizienten, die Art der Abscheidungsvorgänge und die Lage der Halbwellenpotentiale, bez. auf die gesätt. wäßr. Kalomelelektrode, wurden bei 25° in 0,1M-Lösungen von Tetraäthylammoniumperchlorat bestimmt. Es wurden die Reduktionsvorgänge Ti(IV)–Ti(III), V(III)–V(II), V(IV)–V(II), Cr(III)–Cr(II) und Cr(II)–Cr(0) aufgefunden, wobei nur V(III)–V(II) reversibel verläuft.

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Polarographic investigation have been carried out on titanium(III)chloride, titanium(IV)oxoperchlorate, vanadium(III)chloride, vanadium(IV)oxoperchlorate, chromium(III)chloride and chromium(III)perchlorate in 1,2-propanediol-carbonate; the nature of the limiting currents, the diffusion current constants, the diffusion coefficients, the reversibility or irreversibility of the electrode process and the half-wave potentials vs. aqueous saturated calomel electrode have been determined in 0,1M solutions of tetraethylammonium perchlorate at 25°. Reduction waves were found corresponding to Ti(IV)–Ti(III), V(III)–V(II), V(IV)–V(II), Cr(III)–Cr(II) and Cr(II)–Cr(0)

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Mit 2 Abbildungen

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1. Mitt.:V. Gutmann, M. Kogelnig undM. Michlmayr, Mh. Chem.99, 693 (1968).

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2. Mitt.:V. Gutmann, M. Kogelnig undM. Michlmayr, Mh. Chem.99, 699 (1968).     

Arsenic speciation in xylem sap of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm⁻³ arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.