Speciation of arsenic in water samples by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry at trace levels using a post-column reaction system

Anion-exchange HPLC has been combined with hydride generation - atomic absorption spectrometry (HG-AAS) for the routine speciation of arsenite, arsenate, monomethylarsenic acid and dimethylarsinic acid. The sensitivity of the AAS-detection was increased by a post-column reaction system to achieve complete formation of volatile arsines from the methylated species and arsenate. The system allows the quantitative determination of 0.5 microg/l of each arsenic compound in water samples. The stability of synthetical and natural water containing arsenic at trace levels was investigated. To preserve stored water samples, a method for quantitative separation of arsenate at high pH-values with the basic anion-exchange resin Dowex 1x8 was developed.     

Determination of arsenic species in marine organisms by HPLC-ICP-OES and HPLC-HG-QFAAS

Separation and quantification of six arsenic species have been performed in cod, tuna and mussel samples by high performance liquid chromatography (HPLC) using inductively coupled plasma-optical emission spectrometry (ICP-OES) and hydride generation-quartz furnace atomic absorption spectrometry (HG-QFAAS) as detection techniques. It has been shown that arsenic extraction with a water-methanol (11) mixture is sufficiently quantitative for the cod and tuna, in which arsenic is mainly present as arsenobetaine (about 90% of total As extracted). In contrast, only 60% of the element is extracted from the mussels and the chromatograms obtained reveal the presence of an unknown compound. Detection limits are in the g ml^–1 range for the HPLC-ICP-OES technique (quantification of arsenobetaine and arsenocholine) and in the ng ml^–1 range for the HPLC-HG-QFAAS system (quantification of arsenite, arsenate, monomethylarsonic and dimethylarsinic acids).     

Radiochemical studies on the extraction of arsenic(III) by trilaurylamine oxide and benzene from aqueous iodide solutions and its determination in water samples by spectrophotometry

An extraction system consisting of trilaurylamine N-oxide and benzene has been identified as a possible extractant for tracer arsenic (<10^–3 M) from hydrochloric or sulfuric acid solutions with or without iodide. Benzene alone is less efficient as an extractant for arsenic when compared with trilaurylamine oxide dissolved in benzene. The mechanism of extraction is attributed to the formation of hydrated AsCl₃, while the iodide complex is most probably AsI ₄ ^– . The role of the solvent and the other parameters affecting the extraction have been investigated. The results have been employed to determine arsenic in water samples by spectrophotometry using the molybdenum blue method. The extraction procedure was used for the analysis of 10 ml water samples containing 0.2–0.5 g of arsenic.     

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg^–1 soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L^–1 CaCl₂, and 0.05 mol L^–1 (NH₄)₂SO₄ were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC–ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.     

Determination of arsenite and arsenate by differential pulse polarography

Summary Arsenate was determined by differential pulse polarography in acidic solutions in the presence of polyhydroxy compounds. The best medium was found to be 2.0 M aqueous HClO₄ containing 4.5 g d-mannitol in 50 ml solution. The peak heights measured at –0.55 V gave linear calibration curves in the concentration range 20 g/l to 160 mg/l As. Arsenite was similarly determined with mannitol at –0.34 V or without mannitol at –0.42 V. When arsenite and arsenate were present in solution, the simultaneous determination of these compounds in the presence of mannitol was generally not possible because the peak heights at –0.34 V and –0.55 V were influenced by arsenite as well as arsenate. In these cases arsenite was determined at –0.42V in the absence of mannitol. After oxidation of arsenite to arsenate by chlorine water and addition of mannitol, total inorganic arsenic was determined as arsenate at –0.55 V. The arsenate concentration in the sample was found as the difference between the concentrations of total inorganic arsenic and arsenite. The detection limit for arsenite and arsenate was found to be approximately 10 g/l As. This method was successfully used to determine arsenite and arsenate in a synthetic river water sample and some arsenic-containing drinking water samples.

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Bestimmung von Arsenit und Arsenat durch Differential-Pulspolarographie

Zusammenfassung Arsenat wurde durch Differential-Pulspolarographie in saurer Lösung in Gegenwart von Polyhydroxyverbindungen bestimmt. Das günstigste Medium war 2,0 M wäßrige HClO₄ mit 4,5 g d-Mannit in 50 ml. Die bei –0,55V gemessenen Peakhöhen ergaben eine lineare Eichkurve für den Bereich von 20 g/l bis 160 mg/l As. Arsenit wurde auf ähnliche Weise mit Mannit bei –0,34 V oder ohne Mannit bei –0,42 V bestimmt. Bei Anwesenheit von Arsenit + Arsenat in Lösung war eine Simultanbestimmung in Gegenwart von Mannit im allgemeinen nicht möglich, weil die Peakhöhen bei –0,34 V und –0,55 V sowohl von Arsenit als auch von Arsenat beeinflußt werden. In diesen Fällen wurde Arsenit ohne Mannit bei –0,42 V bestimmt. Nach Oxidation zu Arsenat mit Chlorwasser und Zugabe von Mannit wurde dann das Gesamtarsen als Arsenat bei –0,55 V bestimmt; der Arsenatgehalt in der Probe ergab sich aus der Differenz. Die Nachweisgrenze für Arsenit und Arsenat lag bei etwa 10 g/l As. Das Verfahren wurde mit gutem Erfolg für eine synthetische Flußwasserprobe sowie einige Trinkwasserproben angewendet.

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On leave from Jadavpur University, Calcutta, India     

Arsenic speciation in saliva of acute promyelocytic leukemia patients undergoing arsenic trioxide treatment

Arsenic trioxide has been successfully used as a therapeutic in the treatment of acute promyelocytic leukemia (APL). Detailed monitoring of the therapeutic arsenic and its metabolites in various accessible specimens of APL patients can contribute to improving treatment efficacy and minimizing arsenic-induced side effects. This article focuses on the determination of arsenic species in saliva samples from APL patients undergoing arsenic treatment. Saliva samples were collected from nine APL patients over three consecutive days. The patients received 10 mg arsenic trioxide each day via intravenous infusion. The saliva samples were analyzed using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry. Monomethylarsonous acid and monomethylmonothioarsonic acid were identified along with arsenite, dimethylarsinic acid, monomethylarsonic acid, and arsenate. Arsenite was the predominant arsenic species, accounting for 71.8 % of total arsenic in the saliva. Following the arsenic infusion each day, the percentage of methylated arsenicals significantly decreased, possibly suggesting that the arsenic methylation process was saturated by the high doses immediately after the arsenic infusion. The temporal profiles of arsenic species in saliva following each arsenic infusion over 3 days have provided information on arsenic exposure, metabolism, and excretion. These results suggest that saliva can be used as an appropriate clinical biomarker for monitoring arsenic species in APL patients.

Urinary arsenic species in an arsenic‐affected area of West Bengal,India (part III)

Arsenic contamination of groundwater has long been reported in the Mushidabad district of West Bengal, India. We visited 13 arsenic‐affected families in the Makrampur village of the Beldanga block in Mushidabad during 18–21 December 2001 and collected five shallow tubewell‐water samples used general household purposes, four deep tubewell‐water samples used for drinking and cooking purposes, and 44 urine samples from those families. The arsenic concentrations in the five shallow tubewell‐water samples ranged from 18.0 to 408.4 ppb and those in the four deep tubewell‐water samples were from 5.2 to 9.6 ppb. The average arsenite (arsenic(III)), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate (arsenic(V)) in urine were 28.7 ng mg^?1, 168.6 ng mg^?1, 25.0 ng mg^?1 and 4.6 ng mg^?1 creatinine respectively. The average total arsenic was 227.0 ng mg^?1 creatinine. On comparison of the ratio of (MMA + DMA) to total arsenic, the average proportion was 86.7 ± 9.2% (mean plus/minus to residual standard deviation, n = 43). The exception was data for one boy, whose proportion was 8.0%. One woman excreted the highest total arsenic, at 2890.0 ng mg^?1 creatinine. When using 43 of the urine samples (the exception being the one sample obtained from the boy) there were significantly positive correlations (p < 0.01) between arsenic(III) and MMA, between arsenic(III) and DMA and between MMA and DMA. Copyright © 2005 John Wiley & Sons, Ltd.     

Biotransformation of arsenate to arsenosugars by Chlorella vulgaris

Chlorella vulgaris was cultivated in a growth medium containing arsenate concentration of <0.01, 10, 100 and 1000 mg l^?1. Illumination was carried out in 12 h cycles for 5 days. The health status of the culture was monitored by continuous pH and dissolved oxygen (DO) readings. Destructive sampling was used for the determination of biomass, chlorophyll, total arsenic and arsenic species. The chlorophyll a content, the DO and pH cycles were not significantly different for the different arsenate concentrations in the culture. In contrast, biomass production was significantly (p < 0.05) increased for the arsenic(V) treatment at 1000 mg l^?1 compared with 100 mg l^?1. The arsenic concentration in the algae increased with the arsenate concentration in the culture. However, the bioconcentration factor decreased a hundred‐fold with increase of arsenate from the background level to 1000 mg l^?1. The arsenic species were identified by using strong anion‐exchange high‐performance liquid chromatography–inductively coupled plasma mass spectrometry analysis after methanol/water (1 : 1) extraction. The majority (87–100%) of the extractable arsenic was still arsenate; arsenite was found to be between 1 and 6% of total extractable arsenic in the algae. In addition to dimethylarsinic acid, one unknown arsenical (almost co‐eluting with methylarsonic acid) and three different arsenosugars have been identified for the first time in C. vulgaris growing in a culture containing a mixture of antibiotics and believed to be axenic. The transformation to arsenosugars in the algae is not dependent on the arsenate concentration in the culture and varies between 0.2 and 5% of total accumulated arsenic. Although no microbiological tests for bacterial contamination were made, this study supports the hypothesis that algae, and not associated bacteria, produce the arsenosugars. Copyright © 2003 John Wiley & Sons, Ltd.     

On-line preconcentration of arsenic from water samples with an anion-exchanger column coupled to a hydride generation ICP system

Summary An on-line anion-exchange preconcentration hydride generation ICP system for the determination of total inorganic arsenic in water is described. The column was packed with strongly basic anion-exchange resin (AG 1-X8). Experimental conditions including pH of the sample solution, eluent, flow rate of eluent, oxidation states of arsenic and competing anion ions were studied. Compared with the conventional continuous hydride generation ICP, a 9.2-fold improvement in sensitivity was obtained with RSD 1–2% at 100 ng/ml. The detection limit (3) was 0.08 ng/ml. The recoveries in water samples were satisfactory. The system provides complete automation of sample loading, eluting and regenerating of the resin.On leave from Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai, China 200050     

Analytical investigations of phenyl arsenicals in groundwater

Phenylic arsenic compounds are the main contaminants in groundwater at abandoned sites with a history of arsenic containing chemical warfare agents (CWA). A fast and sensitive HPLC-ICP-MS method was developed to determine inorganic arsenic compounds like arsenite and arsenate as well as the degradation products of the arsenic containing warfare agents (phenylarsonic acid, phenylarsine oxide, diphenylarsinic acid). Beside these arsenic species the groundwater samples contained also high iron contents (up to 23 mg/l as Fe(II)) which led to precipitates in the samples after coming into contact with the atmosphere. Preservation immediately after sampling by phosphoric acid has shown that a successful avoidance of any losses of any arsenic species between sampling and analysis was possible. The suggested analytical method was applied to groundwater samples taken from different depths at a polluted site. The main contaminant in the water samples was diphenylarsinic acid (up to 2.1 mg/l) identified by ESI-MS, but also elevated concentrations of inorganic arsenic (up to 240 microg/l) were found.     

Preservation of As(III) and As(V) in some water samples

This paper reports on the behavior of arsenite [As(III)] and arsenate [As(V)] in some water samples at storage under several conditions (pH=2/natural pH, 4°C/20°C). The investigation was carried out using⁷³As as a radiotracer for both forms and with the aid of earlier developed simple speciation methods for differentiation between arsenite and arsenate. Although arsenate is the thermodynamically stable arsenic form, it was observed that arsenate in deionized water is completely converted to the trivalent state; this phenomenon took place in about one week. By monitoring the radioactive As(III) and As(V) over a period of one month in two natural water samples, a fresh water and a sea water sample, it could be concluded that no adsorption occurs on the surface of polyethylene containers, independent of storage conditions. During that period, storage at natural pH values results for both water samples in a gradual oxidation of As(III); the oxidation rate is higher for storage at 20°C. At pH=2 As(III) is fairly stable in fresh water at both storage temperatures. However, in sea water a fast oxidation of As(III) is observed (complete oxidation within 3 d at both temperatures). As(V) is stable at all storage conditions studied.     

Biomethylation of Arsenic in an Arsenic-rich Freshwater Environment

Arsenic circulation in an arsenic-rich freshwater ecosystem was elucidated to detect arsenic species in the river water and in biological samples living in the freshwater environment. Water-soluble arsenic compounds in biological samples were extracted with 70% methanol. Samples containing arsenic compounds in the extracts were treated with 2 mol dm³ of sodium hydroxide and reduced with sodium borohydride. The detection of arsenic species was accomplished using a hydride generation/cold trap/cryofocus/gas chromatography-mass spectrometry (HG/CT/CF/GC-MS) system. The major arsenic species in the river water, freshwater algae and fish are inorganic arsenic, dimethylarsenic and trimethylarsenic compounds, respectively. Trimethylarsenic compounds are also detected in aquatic macro-invertebrates. The freshwater unicellular alga Chlorella vulgaris, in a growth medium containing arsenate, accumulated arsenic and converted it to a dimethylarsenic compound. The water flea Daphnia magna, which was fed on arsenic-containing algae, converted it to a trimethylarsenic species. © 1997 by John Wiley & Sons, Ltd.     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic(III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic(V) to arsenic(III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800°C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2g/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3) of 0.01g/L using a 0.5mL sample. The reagent blank was 0.001±0.0003 absorbance units and the standard deviation of 10 measurements of the 2 g/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

A method for rapid determination of arsenic species in vegetables using microwave‐assisted extraction followed by detection with HPLC hyphenated to inductively coupled plasma‐mass spectrometry

Driven by the significant need for characterization of the chemical speciation of arsenic in food, this work developed a method for rapid determination of four common arsenic species, namely, arsenite, arsenate, monomethyl arsenic acid, and dimethyl arsenic acid, in vegetables using microwave‐assisted extraction, followed by detection with high‐performance liquid chromatography hyphenated to inductively coupled plasma‐mass spectrometry. Initial screening results showed that microwave‐assisted extraction using 1% HNO₃ exhibited the highest overall efficiencies for all arsenic species without causing significant degradation of the organic ones. With the aid of response surface methodology, the optimum conditions established for extraction of arsenic species from vegetables were: 500 mg of freeze‐dried vegetable sample, extracted by closed vessel microwave‐assisted extraction using 10 mL of 2% v/v HNO₃ at 90°C for 17 min. Application of the method in the analysis of 24 market vegetable samples indicates that the extraction efficiencies for total arsenic species were in the range of 91.4–106%. Arsenite and arsenate were found to be the predominant arsenic species in the vegetables, which suggests that vegetable consumption could be an important route of inorganic arsenic exposure for the population with a heavy vegetable diet in arsenic polluted regions.     

The extraction and speciation of arsenic in rice flour by HPLC-ICP-MS

Several solvent mixtures and techniques for the extraction of arsenic (As) species from rice flour samples prior to their analysis by HPLC-ICP-MS were investigated. Microwave-assisted extraction using water at 80 °C for 30 min provided the highest extraction efficiency. Total recoveries of extracted As species were in good agreement with the total As concentrations determined by ICP-MS after microwave-assisted acid digestion of the samples. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMAA) were the main species detected in rice flour samples.     

Simultaneous separation of 17 inorganic and organic arsenic compounds in marine biota by means of high-performance liquid chromatography/inductively coupled plasma mass spectrometry

A method using high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS) has been developed to determine inorganic arsenic (arsenite, arsenate) along with organic arsenic compounds (monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, trimethylarsine oxide, tetramethylarsonium ion and several arsenosugars) in fish, mussel, oyster and marine algae samples. The species were extracted by means of a methanol/water mixture and a dispersion unit in 2 min, with extraction efficiencies ranging from 83 to 107% in the different organisms. Up to 17 different species were determined within 15 min on an anion-exchange column, using a nitric acid gradient and an ion-pairing reagent. As all species are shown in one chromatogram, a clear overview of arsenic distribution patterns in different marine organisms is given. Arsenobetaine is the major compound in marine animals whereas arsenosugars and arsenate are dominant in marine algae. The method was validated with CRM DORM-2 (dogfish muscle). Concentrations were within the certified limits and low detection limits of 8 ng g(-1) (arsenite) to 50 ng g(-1) (arsenate) were obtained.     

Speciation analysis of arsenic in groundwater from Inner Mongolia with an emphasis on acid-leachable particulate arsenic

Arsenic in drinking water affects millions of people around the world. While soluble arsenic is commonly measured, the amount of particulate arsenic in drinking water has often been overlooked. We report here determination of the acid-leachable particulate arsenic and soluble arsenicals in well water from an arsenic-poisoning endemic area in Inner Mongolia, China. Water samples (583) were collected from 120 wells in Ba Men, Inner Mongolia, where well water was the primary drinking water source. Two methods were demonstrated for the determination of soluble arsenic species (primarily inorganic arsenate and arsenite) and total particulate arsenic. The first method used solid phase extraction cartridges and membrane filters to separate arsenic species on-site, followed by analysis of the individual arsenic species eluted from the cartridges and filters. The other method uses liquid chromatography separation with hydride generation atomic fluorescence detection to determine soluble arsenic species. Analysis of acidified water samples using inductively coupled plasma mass spectrometry provided the total arsenic concentration. Arsenic concentrations in water samples from the 120 wells ranged from <1 to ∼1000 μg L⁻¹. On average, particulate arsenic accounted for 39 ± 38% (median 36%) of the total arsenic. In some wells, particulate arsenic was six times higher than the soluble arsenic concentration. Particulate arsenic can be effectively removed using membrane filtration. The information on particulate and soluble arsenic in water is useful for optimizing treatment options and for understanding the geochemical behavior of arsenic in groundwater.     

Determination of toxic and non-toxic arsenic species in urine by microwave assisted mineralization and hydride generation atomic absorption spectrometry

Flow injection — microwave oven — hydride generation — atomic absorption spectroscopy (FI-MO-HG-AAS) has been optimized for the determination of the total and toxic arsenic in urine with and without persulfate, respectively. With microwave oven assisted digestion of urine with 5% (w/v) K₂S₂O₈ and 5% (w/v) NaOH all arsenicals completely can be converted to arsenate, which is determined by HG-AAS to give the total concentration of the six species present in urine. The detection limits of 4–6 g l^–1, the relative standard deviation of 3–7% and the high sample throughput make the methods suitable for rapid routine on-line determination. Application of the proposed procedures to the analysis of urine from people on a diet rich in seafood revealed a significant increase in total urinary arsenic due to the rapid excretion of organoarsenicals. Efficient decomposition and quantitative recovery of all arsenic species in spiked urine is achieved by using 5% K₂S₂O₈ in 5% NaOH at 4.6 ml min^–1, microwave power of 700 W and a 1.5 m coil.     

Modelling and prediction of retention in high-performance liquid chromatography by using neural networks

Summary Two analytical methods have been developed for the determination in water of 18 priority phenolics listed in US EPA method 604 and on EEC list 76/464. A solidphase extraction system using eight different sorbents packed in a precolumn was coupled on-line with a liquid chromatograph with UV detection. The ensuing method uses 50–100 mL of ground water; its performance was compared with that of an off-line method using Empore extraction disks and 1 L water samples. Phenol recoveries varied from <20 to 100% for concentrations in the range 0.1–10 g/L at an acid pH. The presence of the phenols in water was confirmed by using thermospray LC-mass spectrometry in the negative ion mode. The stability of the phenols in water was studied at a 10 g/l level in ground and estuarine water at acid pH (2.5–3) and at 4°C for 1 month. The system was validated by various interlaboratory exercises with samples containing 2,4,6-trichlorophenol and pentachlorophenol at concentrations from 0.1 to 0.5 g/L.     

Use of peat-based sorbents for removal of arsenic compounds

It is important to apply sorbent materials for purification of water from arsenic contamination due to serious arsenic pollution worldwide. We have developed new sorbents based on natural materials that provide a cheap and environmentally friendly alternative. For the first time, peat modified with iron compounds and iron humates were tested for sorption of arsenic compounds. The highest sorption capacity was found in peat modified with iron compounds. We have found that sorption of different arsenic speciation forms was strongly dependent on solution pH, reaction time and temperature. Calculations of the sorption process using thermodynamic parameters indicate the spontaneity of sorption process and its endothermic nature. Sorption kinetics showed that most arsenates are removed within 2 hours, and the kinetics of arsenate sorption on modified peat can be described by the pseudo-second order mechanism.