Arsenic speciation by coupling high-performance liquid chromatography with inductively coupled plasma mass spectrometry

Summary An ICP-MS detector in combination with HPLC has been evaluated for the analysis of six arsenic compounds. The influence of the presence of an organic modifier in the mobile phase on arsenic response and the quality parameters of the analysis are discussed. Detection limits for arsenic species under study range from 10 to 30 pg. The determination of arsenic compounds in solutions simulating fish or sediment extracts has been used to demonstrate the applicability of this technique.     

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.     

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 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.     

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.     

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 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.     

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     

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.     

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     

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.     

The Dawn of Functional Organoarsenic Chemistry

Organoarsenic chemistry was actively studied until the middle of 20th century. Although various properties of organoarsenic compounds have been computationally predicted, for example, frontier orbital levels, aromaticity, and inversion energies, serious concern to the danger of their synthetic processes has restricted experimental studies. Conventional synthetic routes require volatile and toxic arsenic precursors. Recently, nonvolatile intermediate transformation (NIT) methods have been developed to safely access functional organoarsenic compounds. Important intermediates in the NIT methods are cyclooligoarsines, which are prepared from nonvolatile inorganic precursors. In particular, the new approach has realized experimental studies on conjugated arsenic compounds: arsole derivatives. The elucidation of their intrinsic properties has triggered studies on functional organoarsenic chemistry. As a result, various kinds of arsenic-containing π-conjugated molecules and polymers have been reported for the last few years. In this minireview, progress of this recently invigorated field is overviewed.     

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.     

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.     

Arsenic‐Containing Phosphatidylcholines: A New Group of Arsenolipids Discovered in Herring Caviar

A new group of arsenolipids based on cell‐membrane phosphatidylcholines has been discovered in herring caviar (fish roe). A combination of HPLC with elemental and molecular mass spectrometry was used to identify five arsenic‐containing phosphatidylcholines; the same technique applied to salmon caviar identified an arsenic‐containing phosphatidylethanolamine. The arsenic group in these membrane lipids might impart particular properties to the molecules not displayed by their non‐arsenic analogues. Additionally, the new compounds have human health implications according to recent results showing high cytotoxicity for some arsenolipids.     

Species differences in the metabolism of arsenic compounds

Humans are exposed via air, water and food to a number of different arsenic compounds, the physical, chemical, and toxicological properties of which may vary considerably. In people eating much fish and shellfish the intake of organic arsenic compounds, mainly arsenobetaine, may exceed 1000 μg As per day, while the average daily intake of inorganic arsenic is in the order of 10–20 μg in most countries. Arsenobetaine, and most other arsenic compounds in food of marine origin, e.g. arsenocholine, trimethylarsine oxide and methylarsenic acids, are rapidly excreted in the urine and there seem to be only minor differences in metabolism between animal species. Trivalent inorganic arsenic (AsIII) is the main form of arsenic interacting with tissue constituents, due to its strong affinity for sulfhydryl groups. However, a substantial part of the absorbed AsIII is methylated in the body to less reactive metabolities, methylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are rapidly excreted in the urine. All the different steps in the arsenic biotransformation in mammals have not yet been elucidated, but it seems likely that the methylation takes place mainly in the liver by transfer of methyl groups from S-adenosylmethionine to arsenic in its trivalent oxidation state. A substantial part of absorbed arsenate (AsV) is reduced to AsIII before being methylated in the liver. There are marked species differences in the methylation of inorganic arsenic. In most animal species DMA is the main metabolite. Compared with human subjects, very little MMA is produced. The marmoset monkey is the only species which has been shown unable to methylate inorganic arsenic. In contrast to other species, the rat shows a marked binding of DMA to the hemoglobin, which results in a low rate of urinary excretion of arsenic.     

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.     

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.     

砷、锑、铋类药物的应用历史和现状

近年来,由于对主族元素砷、锑、铋的生物功能研究的不断深入,人们已经从仅仅关注它们对人体的生物毒性到开始研究它们在化学药物领域的应用和潜力。本文简要的介绍了砷、锑、铋作为药物应用的历史,综述了近年来砷、锑、铋的化合物在抗癌、治疗白血病、抗寄生虫病和抗菌方面的一些应用,以及用于发现这些药物的靶分子和结合蛋白的现代生物技术。