Blank values, adsorption, pre-concentration, and sample preservation for arsenic speciation of environmental water samples

Arsenic is the focus of public attention because of its toxicity. Arsenic analysis, its toxicity, and its fate in the environment have been broadly studied, still its blank values, adsorption to sampling materials and pre-concentration of water samples as well as stabilization of arsenic compounds in water samples under field conditions have been very little investigated. In this study, we investigate the blank values and adsorption of arsenic compounds for different laboratory materials. We focused our work onto pre-concentration of water samples and how to stabilize arsenic compounds under field conditions. When using glassware for arsenic analysis, we suggest testing arsenic blank values due to the potential release of arsenic from the glass. Adsorption of arsenic compounds on different laboratory materials (<10%) showed little influence on the arsenic speciation. Pre-concentration of methanol-water solutions could result in potential overestimation of arsenic compounds concentrations. Successful pre-concentration of water samples by nitrogen-purge provides an analytical possibility for arsenic compounds with high recoveries (>80%) and low transformation of arsenic compounds. Thus, concentrations as low as 1 ng As l⁻¹ can be determined. Addition of ethylenediaminetetraacetic acid (EDTA) and storage in the dark can decrease the transformation among arsenic compounds in rainwater and soil-pore water for at least a week under field conditions.     

Arsenic speciation in solid biological specimens by temperature-controlled pyrolysis and NAA

A pyrolysis-neutron activation analysis (NAA) procedure has been developed and applied to the speciation of arsenic in solid biological samples. The method involves the retention of the inorganic arsenic in the pyrolysis boat by the addition of NaOH, the volatilization and trapping of the organic arsenic on a cation exchange resin and the subsequent NAA of the resin for the determination of the trapped arsenic. The method, developed with the aid of radiochemically labelled arsenic compounds, has been applied to the determination of the ratio of inorganic to organic arsenic species in commercical shrimps as well as in NBS standard reference materials such as oysters and orchard leaves. The results show different relative amounts of inorganic arsenic content in the samples analysed. In the shrings the fraction of inorganic arsenic was of the order of 20%, in the oysters the inorganic arsenic consfituted 60% of the total arsenic concentration while in the samples of vegetable origin more than 98% of the arsenic was of inorganic nature.     

Speciation of Arsenic Compounds in the Urine of Rats Orally Exposed to Dimethylarsinic Acid Ion Chromatography with ICP–MS as an Element-Selective Detector

A combined ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP—MS) system as an element-selective detector has been used for the determination of arsenic compounds. Seven arsenic compounds were separated by cation-exchange chromatography. Subsequently, the separated arsenic compounds were directly introduced into the ICP—MS and were detected at m/z =75. Detection limits for the seven arsenic compounds ranged from 0.8 to 3.8 μg As/l. The IC–ICP–MS system was applied to the determination of arsenic compounds in the urine of dimethylarsinic acid (DMAA)-exposed rats. DMAA was the most abundant arsenic compound detected. Arsenous acid, monomethylarsonic acid and trimethylarsine oxide were also detected.     

Arsenic and its speciation analysis using high-performance liquid chromatography and inductively coupled plasma mass spectrometry

It is known that arsenic has different toxicological properties dependent upon both its oxidation state for inorganic compounds, as well as the different toxicity levels exhibited for organic arsenic compounds. The field of arsenic speciation analysis has grown rapidly in recent years, especially with the utilization of high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS), a highly sensitive and robust detector system. Complete characterization of arsenic compounds is necessary to understand intake, accumulation, transport, storage, detoxification and activation of this element in the natural environment and living systems. This review describes the essential background and toxicity of arsenic in the environment, and more importantly, some currently used chromatographic applications and sample handling procedures necessary to accurately detect and quantify arsenic in its various chemical forms. Applications and work using only HPLC-ICP-MS for arsenic speciation of environmental and biological samples are presented in this review.     

The determination of arsenic in treated wood

The SCHULEK AND VON VILLECZ method for the determination of arsenic in organic compounds has been applied to the determination of arsenic in wood Copper and chromium do not interfere     

Reactive supercritical fluid extraction and chromatography of arsenic species

Reactive supercritical fluid extraction has been used for the speciation of organic (DMA and MMA) and inorganic (As(III) and As(V)) arsenic compounds in solid samples. Derivatization with thioglycolic acid methylester (TGM) was performed in supercritical carbon dioxide. Different extraction conditions have been tested. The arsenic derivatives have been analyzed by GC. A capillary-SFC method was evaluated for the analysis of the TGM derivatives and compared with GC.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

The determination of arsenic and selenium by HPLC combined with alternating current plasma detection and post-column hydride formation

A helium alternating current plasma detector in combination with HPLC has been evaluated for the determination of arsenic and selenium-containing compounds after post-column hydride generation. The construction, operation, and optimization of the system is presented. Detection limits for the compounds under study ranged from 45–60 pg/s. Determination of arsenic and selenium in spiked river water samples has been used to demonstrate the applicability of the technique.     

Determination of arsenic compounds in reference materials by HPLC-(UV)-HG-AFS

Arsenic compounds were determined in six reference materials of biological origin. None of them has yet been certified for arsenic compounds but some are in the process of certification; for most of these reference materials indicative literature values are available. Eight commonly used arsenic standards were used for quantification using a recently developed hyphenated speciation system comprising high performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS), interfaced via a UV-photoreactor and a hydride generation (HG) unit. Absolute detection limits were ca. 0.2 and 0.4 ng As for separation on anion and cation exchange columns, respectively. Our results agree well with indicative literature values which were generated by different authors using various separation and detection methods. The HPLC-(UV)-HG-AFS system validated in this way is suitable for quantification of eight arsenic compounds. Moreover, the system is capable of separation of at least six more compounds in the mentioned reference materials, of which two could be attributed to arsenosugars (OH and phosphodiester form) but due to the lack of standards, quantification was not possible. For accurate and extensive speciation analysis the availability of certified reference materials and standards for arsenic compounds should be promoted.     

Speciation of arsenic compounds by coupling high-performance liquid chromatography with inductively coupled plasma mass spectrometry

There is considerable evidence that toxicity and physiological behavior of arsenic depends on its chemical forms. Arsenic speciation became therefore the subject of increasing interest in recent years. A sensitive method for the determination of arsenic species has been developed. The proposed procedure involves the use of high-performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Six arsenic compounds were separated by anion-exchange chromatography with isocratic elution using tartaric acid as mobile phase with an elution order: arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid. The chromatographic parameters affecting the separation of the arsenic species were optimized. Analytical characterization of the method has been realized with standard solutions. The detection limits for six arsenic compounds were from 0.04 to 0.6 g/L as As element. The repeatability (expressed by R.S.D) was better than 7% for all investigated compounds. The HPLC-ICP-MS system was successfully applied to the determination of arsenic compounds in environmental and biological samples in g/L level.     

The discovery of hidden arsenic species in coastal waters

The analysis of ultraviolet (UV)-irradiated and untreated seawater samples has shown that the dissolved arsenic content of marine waters cannot be completely determined by hydride generation–atomic absorption spectrophotometry without sample pretreatment. Irradiation of water samples obtained during a survey of arsenic species in coastal waters during the summer of 1988 gave large increases in the measured speciation. Average increases in the measured speciation. Average increases in total arsenic, monomethylarsenic and dimethylarsenic were 0.29 μg As dm^?3 (25%), 0.03 μg As dm^?3 (47%) and 0.12 μg As dm^?3 (79%), respectively. Overall, an average 25% increase in the concentration of dissolved arsenic was observed following irradiation. This additional arsenic may be derived from compounds related to algal arsenosugars or to their breakdown products. These do not readily yield volatile hydrides when treated with borohydride and are not therefore detected by the normal hydride generation technique. This has important repercussions as for many years this procedure, and other analytical procedures which are equally unlikely to respond to such compounds, have been accepted as giving a true representation of the dissolved arsenic speciation in estuarine and coastal waters. A gross underestimate may therefore have been made of biological involvement in arsenic cycling in the aquatic environment.     

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.     

A novel method for the estimation of arsenic(V) in organic compounds

A novel method for the determination of arsenic(V) in organic compounds has been developed by reducing combined arsenic(V) to arsenic(III) in aqueous acetic acid medium with zinc dust. In some cases, addition of ethyl alcohol is necessary to dissolve the compound and to keep the arsenic(III) compound in solution. The arsenic(III) is titrated with iodine and the end-point is detected visually with starch as indicator or potentiometrically.     

Arsenic compounds in marine and terrestrial organisms: Analytical,chemical and biochemical aspects

Arsenic has a reputation as a poison, because arsenic trioxide was used during medieval times as an agent for murder. Lingering memories of these events make any arsenic-containing material suspect. Toxicity is a property of a specific compound and varies with the composition and structure of compounds. Developments in analytical methodology made it possible not only to determine total arsenic in a variety of matrices but also arsenic compounds. Knowledge about the arsenic cycle in marine systems has expanded considerably during the past decade. The marine arsenic cycle appears to be more complex than the cycle in the terrestrial environment. More attention must be given to the minor arsenic-containing compounds detected in organisms and experiments should be undertaken that provide information about the biochemical pathways used for the transformation of arsenic compounds.     

The simultaneous microdetermination of carbon,hydrogen, arsenic,or selenium in organic compounds

Simple modifications have been described for the simultaneous microdetermination of carbon, hydrogen, and arsenic or selenium in organic compounds using the rapid straight empty tube combustion technique. A silica insertion tube placed in the combustion tube at the open end of the ignition capsule and cooled via external exposure of the combustion tube around it to a stream of air, was found to be suitable for the quantitative retention of arsenic trioxide produced during the combustion of organo-arsenic compounds. The same modification was proved to be suitable for complete trapping of selenium dioxide produced in the combustion of organo-selenium compounds. In the latter case, the insertion tube was packed at one end with a short silica wool plug and cooling it with air is unnecessary.Using these simple modifications, accurate and reproducible carbon, hydrogen, and arsenic or selenium results were obtained in the analysis of a wide range of organic compounds containing arsenic or selenium. The conventional gravimetric finish was employed for the evaluation of three elements.     

Arsenic solubility, mobility and speciation in the deposits from a copper production waste storage

The sediments in large pond for discharge of waste products of metallurgical activity were studied with respect to the valence forms of arsenic and its mobility. A sequential extraction procedure for arsenic compounds was applied and optimized according to the nature of analyzed products. During the first stage, the content of water-soluble arsenic compounds was determined, during the second—HCl-soluble forms and during the third—compounds soluble in sodium hydroxide. The optimum conditions for leaching arsenic from sediments (sample weight, concentration and volume of extractants, time of treatment) were established for each fraction.Speciation studies for determining As(III) and As(V) were carried out in the obtained arsenic extracts. The ability of the proposed sequential extraction procedure to specify the valence forms of inorganic arsenic was evaluated using model samples with added As(III) and As(V) and the recovery of spikes has been assessed. It was found that oxidation of As(III) and processes of sorption and sedimentation of As(V) proceed upon dissolution. A depth profiling was performed of the content of diverse forms of Às in two sites. The content of water-soluble As does not exceed 7.4% of total As in the sediments, As(III) being lower than 7.4% of that of the extracted As. The bulk of arsenic compounds (above 78% As) is dissolved in 2M HCl, and As(V) was found to be more than 94% of extracted arsenic. The analytical features of the procedure are as follow: precision, evaluated through the repeatability w > 0.96 and accuracy, estimated by the recovery above 93%, calculated on the basis of a twice repeated analysis of a series of 9 samples.     

Raman spectroscopy of selected arsenates--implications for soil remediation

The contamination of soils with heavy metals such as As, Cr and Cu is of great importance; the remediation of such soils even more so. Arsenic compounds are prevalent in soils either through leaching of mine tailings, the use of Cu/Cr/As as a wood preservative or through the use of arsenic in cattle dips. The arsenic compounds in soils and leachates can be highly reactive and mobile, resulting in the formation of metal arsenate compounds. Of these compounds, one such set of minerals that can be formed is the vivianite arsenate minerals. Raman spectroscopy has been used to characterise the vivianite arsenates and to identify arsenic contaminants in a soil.     

Determination of total arsenic and speciation of arseno-betaine in marine fish by means of reaction — headspace gas chromatography utilizing flame-ionization detection and element specific spectrometric detection

Marine organisms contain amounts of arsenic ranging from less than 1 μg/g to more than 10 μg/g. In food examinations usually total arsenic is determined, rarely As(III) and As(V) additionally. Rating marine food according to its total arsenic contents without further speciation, would involve an overcritical assessment. Due to the lack of suitable methods for routine analysis in food-control, the “organic” moiety remains unspecified. Only after performing a systematic research onto the real existence of arsenic and its compounds relevant to marine organisms, a toxicological evaluation can be carried out. As to its quantitative occurrence and its negligible toxic relevance arsenobetaine is of decisive importance. Therefore a reliable method has been developed based on headspace gas chromatography after chemical reaction. The predominant role of arsenobetaine in the organic arsenic moiety as well as in total arsenic in marine fish could thus be demonstrated.     

Methylation of inorganic arsenic by arsenic-tolerant freshwater algae

Five arsenic-resistant freshwater algae which had been isolated from an arsenic-polluted environment were studied for the biotransformation of arsenic compounds accumulated by them from the aqueous phase. The algal cells bioaccumulating arsenic were digested by 2 mol dm^?3 NaOH at 95°C, the As? C bonds except for As? CH₃ were cleaved by the treatment and the methylated arsenic compounds were reduced to the corresponding arsines by sodium borohydride (hydride generation). The arsines were chromatographically separated on the basis of their boiling-point difference and determined by atomic absorption spectrophotometry. Methylated arsenic compounds were found in all algal cells. The predominant arsenic species in the cells, however, were non-methylated arsenic compounds which were mainly present in the residue of a chloroform–methanol extract. The non-methylated arsenic compounds were found to be not present in the free inorganic arsenic substrate and to be bound strongly with proteins or polysaccharides in the cells. Methylated arsenic compounds were found mainly in the lipid-soluble fractions and the major form was a dimethylarsenic compound. Trimethyl- and monomethyl-arsenic compounds were detected but at very low level. The dimethylarsinic acid was not present in the free form in the lipid-soluble fraction and should be bound with a lipid molecule. It was also found that the accumulation of arsenic by Nostoc occurred only in living cells.     

Methylated arsenic species in estuarine porewaters

Inorganic arsenic, monomethylarsenic and dimethylarsenic species have been observed in samples of sediment porewater collected from the Tamar Estuary in South-West England. Porewater samples were collected using in situ dialysis. The arsenic species were separated by hydride generation and concentrated by liquid nitrogen trapping, prior to analysis by directly coupled gas chromatography-atomic absorption spectroscopy. The predominant dissolved arsenic species present was inorganic arsenic (5-62 m?g dm^?3). However, this is the first time significant concentrations of methylated arsenic species have been quantified in estuarine porewaters (0.04–0.70 m?g dm^?3), accounting for between 1 and 4% of the total dissolved arsenic. The presence of methylated arsenic compounds in porewaters is attributed to in situ environmental methylation, although the possibility of methylated arsenic species being derived from biological debris cannot be excluded.     

Miniaturised isotachophoretic analysis of inorganic arsenic speciation using a planar polymer chip with integrated conductivity detection

A new method allowing the analysis of inorganic arsenic species using isotachophoresis has been developed. This method has been shown to be suitable for use on both miniaturised planar polymer separation devices and capillary scale devices. A poly(methyl methacrylate) chip with integrated conductivity electrodes has been successfully used for the rapid analysis of inorganic arsenic species in under 600 s. Limits of detection of 1.8 mg l⁻¹ and 4.8 mg l⁻¹ for arsenic(V) and arsenic(III), respectively, have been achieved with the miniaturised device. The device has also been used to perform the simultaneous separation of arsenic(III), arsenic(V), antimony(III), molybdenum(VI) and tellurium(IV).