Electrochemical methods for the determination of total arsenic and arsenic compounds

The determination of total arsenic and of arsenic compounds in biological and inorganic samples is a task frequently encountered by analysts. Several elecrochemical methods have been developed for the determination of total arsenic (generally after mineralization of the sample), arsenite, arsenate, methylarsonic acid and dimethylarsinic acid. The electrochemical behavior of several other organic arsenic compounds was also studied. This paper reviews these electrochemical methods, their application to environmental samples, and the problems encountered in the electrochemical determination of arsenic and arsenic compounds.     

Industries using arsenic and arsenic compounds

This paper reviews industries using arsenic and arsenic compounds such as wood preservatives and agricultural chemicals, the use of arsenic trioxide in glass manufacture, and the applications of metallic arsenic in non-ferrous alloys and of high-purity arsenic in the electronics industry.     

Tests for elemental sulphur and arsenic based on the formation of arsenic sulphides

Summary Tests for elemental sulphur and arsenic have been based on the formation of arsenic sulphides, dissolution in ammonia and reaction with lead solution. A further test for arsenic employs the reaction with thiosulphate. Antimony, tin and selenium do not interfere. The limit of identification is 5 g for sulphur and 3 g for arsenic.

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Zusammenfassung Es werden Nachweise für elementaren Schwefel und elementares Arsen beschrieben. Sie beruhen auf der Bildung von Arsensulfiden aus den Elementen und Reaktion mit Bleilösung nach Auflösung in Ammoniak; für Arsen wird au\erdem die Reaktion mit Thiosulfat benutzt. Antimon, Zinn und Selen stören nicht. Die Nachweisgrenze beträgt für Schwefel 5 g und für Arsen 3 g.

     

Speciation studies for arsenic and mercury-applications and prospects

Methods are described for the speciation of arsenic and mercury in biological and environmental materials. For arsenic various methods were developed to distinguish between more or less toxic arsenic compounds and non-toxic compounds. For the determination of methylmercury a modification of the Westöö procedure was applied for higher contents as well as anion exchange down to levels below 0.1 g/kg in solids and below 0.1 ng/1 in liquids.     

Substoichiometric speciation for inorganic arsenic and methylated arsenic and its application to samples of marine organisms

A substoichiometric isotope-dilution method is described for the determination of monomethylarsonate, MeAs(V), and dimethylarsinate, Me₂As(V). After the separation of MeAs(V) and Me₂As(V) by extraction as their iodides into benzene, these methylated arsenic species are complexed with a substoichiometric amount of diethyldithiocarbamate in benzene, and the uncomplexed methylarsenic species are removed. The relative standard deviations for the substoichiometric extraction of MeAs(V) and Me₂As(V) are 0.55% and 1.1%, respectively. This substoichiometric speciation of methylated arsenic together with an earlier substoichiometric method for speciation of inorganic arsenic species was applied to the speciation of arsenic in an acid-digested solution of a macro-algae sample. It was demonstrated that almost all the arsenic in this solution was Me₂As(V) even after the digestion with nitric acid.     

Distribution of inorganic arsenic and methylated arsenic in marine organisms

Inorganic arsenic and methylated arsenic compounds in 60 specimens of marine organisms were investigated by hydride generation derivatization and cold-trap gas chromatography–mass spectrometry (GC MS). Chloroform–methanol extracts from seaweeds, shellfish, fish, crustaceans and other marine organisms were separated into water-soluble and lipid-soluble fractions. The arsenic compounds in each fraction were identified and analysed as arsine, methylarsine, dimethylarsine and trimethylarsine. Trimethylarsenic compounds were distributed mainly in the water-soluble fraction of muscle of carnivorous gastropods, crustaceans and fish. The amounts of dimethylated arsenic compounds were found to be larger than that of trimethylated arsenic in the lipid-soluble fraction of fish viscera. Dimethylated arsenic compounds were distributed in the water-soluble fraction of Phaeophyceae.     

Determination of arsenic and arsenic compounds in natural gas samples

Organic arsenic compounds (trialkylarsines) present in natural gas were extracted by 10 cm³ of concentrated nitric acid from 1 dm³ of gas kept at ambient pressure and temperature. The flask containing the gas and the acid was shaken for 1 h on a platform shaker set at the highest speed. The resulting solution was mixed with concentrated sulfuric acid and heated to convert all arsenic compounds to arsenate. Total arsenic was determined in the mineralized solutions by hydride generation. The arsenic concentrations in natural gas samples from a number of wells in several gas fields were in the range 0.01–63 μ As dm^?3. Replicate determinations of arsenic in a gas sample with an arsenic concentration of 5.9 μ dm^?3 had a relative standard deviation of 1.7%. Because of the high blank values, the lowest arsenic concentration that could be reliably determined was 5 ng As dm^?3 gas. Analysis of nonmineralized extracts by hydride generation identified trimethylarsine as the major arsenic compound in natural gas. Low-temperature gas chromatography-mass spectrometry showed more directly than the hydride generation technique, that trimethylarsine accounts for 55–80% of the total arsenic in several gas samples. Dimethylethylarsine, methyldiethylarsine, and triethylarsine were also identified, in concentrations decreasing with increasing molecular mass of the arsines.     

Determination of urinary arsenic and impact of dietary arsenic intake

An analytical method based on microwave decomposition and flow injection analysis (FIA) coupled to hydride generation atomic absorption spectrometry (HGAAS) is described. This is used to differentiate arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) from organoarsenic compounds usually present in seafood. Without microwave digestion, direct analysis of urine by HGAAS gives the total concentration of As(III), As(V), MMA and DMA because organoarsenic compounds such as arsenobetaine, usually found in most seafood, are not reducible upon treatment with borohydride and therefore cannot be determined by using the hydride generation technique. The microwave oven digestion procedure with potassium persulfate and sodium hydroxide as decomposition reagents completely decomposes all arsenicals to arsenate and this can be measured by HGASS. Microwave decomposition parameters were studied to achieve efficient decomposition and quantitative recovery of arsenobetaine spiked into urine samples. The method is applied to the determination of urinary arsenic and is useful for the assessment of occupational exposure to arsenic without intereference from excess organoarsenicals due to the consumption of seafood. Analysis of urine samples collected from an individual who ingested some seafood revealed that organoarsenicals were rapidly excreted in urine. After the ingestion of a 500-g crab, a 10-fold increase of total urinary arsenic was observed, due to the excretion of organoarsenicals. The maximum arsenic concentration was found in the urine samples collected approximately between 4 to 17 hr after eating seafood. However, the ingestion of organoarsenic-containing seafoods such as crab, shrimp and salmon showed no effect on the urinary excretion of inorganic arsenic, MMA and DMA.     

Quantitative distribution analysis for boron and arsenic in silicon-semiconductors

Summary Proceeding from the technological requirements for semiconductor characterization the progress and limitations of quantitative distribution analysis for B and As in silicon semiconductors by ionprobe microanalysis are presented. It is shown that by use of new instrumental technology the detection power for extreme trace analysis of dopant elements can be increased significantly and that development of suitable quantification procedures enables quantitative distribution analysis to be performed with good accuracy. The information obtained provides a basis for establishing more accurate diffusion models for highly doped materials.

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Quantitative Verteilungsanalyse von Bor und Arsen in Silizium-Halbleitern

Zusammenfassung Ausgehend von den technologischen Anforderungen an die Charakterisierung von Halbleitermaterialien wurden neue Entwicklungen und deren Limitierungen in der quantitativen Verteilungsanalyse von B und As in Silizium-Halbleitern beschrieben. Es wurde gezeigt, daß der Einsatz der Ionenstrahlmikroanalyse in ihrer neuesten instrumentellen Realisierung eine wesentliche Verbesserung des Nachweisvermögens für Dotierungselemente ermöglicht und daß durch die Anwendung geeigneter Quantifizierungsmethoden eine hohe Richtigkeit der Verteilungsanalyse erzielt werden kann. Die gewonnenen Informationen dienen als Grundlage für die Entwicklung verbesserter mathematischer Modelle für die Beschreibung von Diffusionsprozessen in hochdotierten Halbleitermaterialien.

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Presented at the 10th Kolloquium über metallkundliche Analyse, Wien, 3.–5. November 1980.

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Dedicated to Prof. Dr. Hanns Malissa on the occasion of his 60th birthday.     

Polarographic determination of copper, arsenic and arsenic in copper arsenite

A method is proposed in which Cu^II, As^III and As^v can be determined in copper arsenite without prior separation. It is based on the fact that Cu^II and As^III yield prominent, distinguishable, widely-separated cathodic polarographic waves in a 0.1M LiCl-0.01M EDTA—0.001M LiOH solution using a dropping mercury electrode, whereas As^v does not give a wave in this medium. The As^v is determined by difference after reduction with sulphurous acid.     

Fluoride-fluorosulfates of arsenic (V) and arsenic (III)

The synthesis of AsF₃(SO₃F)₂ by the reaction AsF₃ + S₂O₆F₂→AsF₃(SO₃F)₂ is described. Various alternate routes leading to similar arsenic (V) fluoride-fluorosulfates are discussed. All materials are clear, viscous, strongly associated liquids of the general formula AsF_n(SO₃F)_5?n, with n ranging from about 2 to 4. The presence of fluorosulfate bridges is ascertained by IR and Raman spectra.The spectroscopic investigation is also extended to arsenic (III) fluoride- fluorosulfates.     

NIES certified reference materials for arsenic speciation

 The National Institute for Environmental Studies (NIES) recently prepared two candidate certified reference materials (CRMs) for arsenicals to meet the growing demand for the quality assurance of arsenic speciation analysis. The NIES candidate CRM No. 14 Brown Alga was prepared from Hijiki seaweed for the certification of inorganic arsenic content, and No. 15 Scallop was prepared from adductor muscle of scallop for the certification of arsenobetaine content. The preparation of the candidate CRMs is briefly described. Cooperative analyses for total arsenic content of the candidate CRMs have been underway. The preliminary speciation analysis at NIES revealed difficulty in establishing suitable conditions for extracting arsenic species from the materials. Chromatograms of arsenic species by a high performance liquid chromatography-inductively coupled plasma mass spectrometric detection system are presented to provide information about arsenic species present in these candidate CRMs.     

Capillary electrophoresis for the speciation of arsenic

Capillary zone electrophoresis (CZE) with on-line UV-detection was used for the determination of arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine. The method is simple and rapid (<10 min) and allows the determination of six different arsenic species without sample pretreatment. Several instrumental parameters were studied to obtain the best performance (pH of buffer, injection mode, injection time, applied voltage). To determine the arsenic compounds, the instrument was used with a negative potential applied to the injection side of the capillary so that the anions can migrate towards the anode because of their own mobility and charge. The capillary wall was coated with an electro-osmotic flow modifier which reversed the electro-osmotic flow and thus increased also the overall migration of the anions towards the anode. The influence of high concentrations of matrix components such as NaCl, KNO₃ and NaNO₃, as well as the presence of acids such as HNO₃ and HCl was studied. CZE was used for the determination of the oxidation state of arsenic in percolate waters and in the leachate of solidified arsenic containing waste. The lowest detectable concentration was about 100 g/l. A comparison with the results obtained with hydride generation coupled to ICP-MS was made.     

Chitosan based composite sorbents for arsenic removal

Russian Chemical Bulletin - The possibilities of using chitosan and its composites with transition metal oxides for arsenic removal from solutions with low concentrations are discussed. Methods for...     

Hydride-trapping techniques for the speciation of arsenic

The determination of arsenic species by the trapping of volatile hydrides prior to atomization in the light path of an atomic absorption spectrometer is described and its operation in the measurement of arsenic species in the marine environment are discussed. Examples are drawn from the analysis of Tamar estuary water and sediment interstitial (pore) waters and from studies of the temporal variation of dimethylarsenic in coastal waters. Improvements in both the design and operation of the technique have resulted in enhanced performance. Baseline resolution of inorganic arsenic, monomethylarsenic and dimethylarsenic is now possible and trimethylarsine is resolved. Ultraviolet photolysis of arsenobetaine and arsenocholine gives partial conversion to trimethylarsine oxide. This can be employed in the qualitative appraisal of the presence of trimethylarsenic species. Current detection limits (3 sigma) for inorganic, mono- and di-methylarsenic lie in the range 19 to 61 pg absolute, giving 19–61 ng/1 concentration detection limits for 1 ml samples. This can be improved even further by using larger sample volumes. The properties of the analysis system when presented with various arsenic species are described. A ca. 10% loss of arsenite occurs in samples stored at —20 °C and immediate freezing of samples in liquid nitrogen is recommended.     

Electrochemical screening procedure for arsenic contaminated soils

Voltammetry of immobilized microparticles was used to find arsenic and heavy metals in contaminated soils from areas with long history of industrial development. Traditional sample dissolution and extraction procedures are time consuming and might distort the chemical equilibrium of the sample causing a change in the original physicochemical forms of distribution. A minute amount of sample was physically attached to the carbon paste working electrode surface and an anodic differential pulse voltammogram was obtained without disturbing the original equilibria. The position of the peaks revealed the presence of Pb and Cu and As(V) and As(III) for the most contaminated soils. As(III) was detected when its percentage in soil was more than 0.001% (expressed as As₂O₃). The limit of detectability was strongly dependent on the presence of iron(III) which increased the signal 10 times.     

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1 M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1 M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.     

Methods for the separation and quantification of arsenic species in SRM 2669: arsenic species in frozen human urine

Two independent liquid chromatography inductively coupled plasma-mass spectrometry (LC/ICP-MS) methods for the separation of arsenic species in urine have been developed with quantification by standard additions. Seven arsenic species have been quantified in a new NIST frozen human urine Standard Reference Material (SRM) 2669 Arsenic Species in Frozen Human Urine, Levels 1 and 2. The species measured were: arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine (AB), arsenocholine (AC), and trimethylarsine oxide (TMAO). The purity of each arsenic standard used for quantification was measured as well as the arsenic species impurities determined in each standard. Analytical method limits of detection (L _D) for the various species in both methods ranged from 0.2 to 0.8 μg L⁻¹ as arsenic. The results demonstrate that LC/ICP-MS is a sensitive, reproducible, and accurate technique for the determination of low-level arsenic species in urine. Measurements of the arsenic species 3 years after initial production of the SRM demonstrate the stability of the arsenic species in the urine reference material.     

Coulometric stripping potentiometry for arsenic(III)

Calibration-free determination of As^III in the presence of As^V using coulometric stripping potentiometry is described. As^III, in the concentration range 0.01-2 mg/L, is quantitatively reduced to elemental arsenic and simultaneously dissolved in gold codeposited onto a glassy carbon substrate by electrolysis for 4 minutes at −0.50 V (vs. Ag/AgCl (0.01 MCl⁻)) in 12 μL samples containing 3 M hydrochloric acid and 10 mg/L gold(III). Selectivity between arsenic(III) and (V) is achieved by proper control of the deposition potential and by minimizing the gold(III) concentration and the time between addition of gold(III) and commencement of analysis.