Determination of various arsenic species by flow injection hydride generation atomic absorption spectrometry: investigation of the effects of the acid concentration of different reaction media on the generation of arsines

High sensitivity atomic fluorescence spectroscopy for the detection of AsIII by selective electrolysis of arsenic on nanoflowers-like Fe/NFE

Modified electrosynthetic sample introduction technique is a reliable means of solving the problem of high sensitivity analysis of trace arsenite. This article attempts to achieve selective electroreduction of AsIII through the construction of electrode surfaces with different structures and materials from the perspective of interface reactions. Among the four transition metal modifiers, the iron modified nickel foam electrode with nano-flower structure documented higher efficiency in inducing arsenic reduction and better species selectivity. Systematic electrochemical and spectroscopic tests suggest that strong adsorption effect between Fe and AsIII, appropriate hydrogen evolution potential, and catalytic activity jointly promote efficient electroreduction of AsIII. Optimization based on electrode materials and electrolysis conditions, with high sensitivity, wide linear range (0.1-50 μg L-1), and excellent species selectivity, this paper offers an efficient and economic sample introduction method for trace AsIII/V selective atomic spectroscopy direct determination.

Non-chromatographic Speciation of As by HG Technique-Analysis of Samples with Different Matrices

The applicability of the hydride generation (HG) sample introduction technique combined with different spectrochemical detection methods for non-chromatographic speciation of toxic As species, i.e., As(III), As(V), dimethylarsinate (DMA) and monomethylarsonate (MMA), in waters and other environmental, food and biological matrices is presented as a promising tool to speciate As by obviating chromatographic separation. Different non-chromatographic procedures along with speciation protocols reported in the literature over the past 20 year are summarized. Basic rules ensuring species selective generation of the corresponding hydrides are presented in detail. Common strategies and alternative approaches are highlighted. Aspects of proper sample preparation before analysis and the selection of adequate strategies for speciation purposes are emphasized.

Analytical Methodologies for the Determination of Organoarsenicals in Edible Marine Species: A Review

Setting regulatory limits for arsenic in food is complicated, owing to the enormous diversity of arsenic metabolism in humans, lack of knowledge about the toxicity of these chemicals, and lack of accurate arsenic speciation data on foodstuffs. Identification and quantification of the toxic arsenic compounds are imperative to understanding the risk associated with exposure to arsenic from dietary intake, which, in turn, underscores the need for speciation analysis of the food. Arsenic speciation in seafood is challenging, owing to its existence in myriads of chemical forms and oxidation states. Interconversions occurring between chemical forms, matrix complexity, lack of standards and certified reference materials, and lack of widely accepted measurement protocols present additional challenges. This review covers the current analytical techniques for diverse arsenic species. The requirement for high-quality arsenic speciation data that is essential for establishing legislation and setting regulatory limits for arsenic in food is explored.

Validation and inter-laboratory study of selective hydride generation for fast screening of inorganic arsenic in seafood

It is advisable to monitor and regulate inorganic arsenic (iAs) in food and feedstuff. This work describes an update and validation of a method of selective hydride generation (HG) with inductively coupled plasma mass spectrometry (ICP-MS) for high-throughput screening of iAs content in seafood samples after microwave-assisted extraction with diluted nitric acid and hydrogen peroxide. High concentration of HCl (8 M) for HG along with hydrogen peroxide in samples of a same concentration as used for extraction leads to a selective conversion of iAs to volatile arsine that is released and transported to the detector. A minor contribution from methylarsonate (≈20% to iAs) was found, while HG from dimethylarsinate, trimethylarsine oxide is substantially suppressed (less than 1% to iAs). Methodology was applied to Certified Reference Materials (CRMs) TORT-3, DORM-3, DORM-4, DOLT-4, DOLT-5, PRON-1, SQID-1 and ERM-CE278k, in some of them iAs has been determined for the first time, and to various seaweed samples from a local store. The results were always compared with a reference method and selectivity of iAs determination was evaluated. An inter-laboratory reproducibility was tested by comparative analyses of six fish and four seaweed samples in three European laboratories, with good agreement of the results. The method of HG-ICP-MS is sensitive (limit of detection 2 μg kg^-1 iAs), well suited for screening of large number of samples and selective at iAs concentration levels at which maximum limits are expected to be set into EU legislation for marine samples.

Arsenic Speciation of Waters from the Aegean Region, Turkey by Hydride Generation: Atomic Absorption Spectrometry

Arsenic in drinking water is a serious problem for human health. Since the toxicity of arsenic species As(III) and As(V) is different, it is important to determine the concentrations separately. Therefore, it is necessary to develop an accurate and sensitive method for the speciation of arsenic. It was intended with this work to determine the concentrations of arsenic species in water samples collected from Izmir, Manisa and nearby areas. A batch type hydride generation atomic absorption spectrometer was used. As(V) gave no signal under the optimal measurement conditions of As(III). A certified reference drinking water was analyzed by the method and the results showed excellent agreement with the reported values. The procedure was applied to 34 water samples. Eleven tap water, two spring water, 19 artesian well water and two thermal water samples were analyzed under the optimal conditions.

Achieving 100% Efficient Postcolumn Hydride Generation for As Speciation Analysis by Atomic Fluorescence Spectrometry

An experimental setup consisting of a flow injection hydride generator coupled to an atomic fluorescence spectrometer was optimized in order to generate arsanes from tri- and pentavalent inorganic arsenic species (iAs(III), iAs(V)), monomethylarsonic acid (MAs(V)), and dimethylarsinic acid (DMAs(V)) with 100% efficiency with the use of only HCl and NaBH4 as the reagents. The optimal concentration of HCl was 2 mol L(-1); the optimal concentration of NaBH4 was 2.5% (m/v), and the volume of the reaction coil was 8.9 mL. To prevent excessive signal noise due to fluctuations of hydride supply to an atomizer, a new design of a gas-liquid separator was implemented. The optimized experimental setup was subsequently interfaced to HPLC and employed for speciation analysis of arsenic. Two chromatography columns were tested: (i) ion-pair chromatography and (ii) ion exchange chromatography. The latter offered much better results for human urine samples without a need for sample dilution. Due to the equal hydride generation efficiency (and thus the sensitivities) of all As species, a single species standardization by DMAs(V) standard was feasible. The limits of detection for iAs(III), iAs(V), MAs(V), and DMAs(V) were 40, 97, 57, and 55 pg mL(-1), respectively. Accuracy of the method was tested by the analysis of the standard reference material (human urine NIST 2669), and the method was also verified by the comparative analyses of human urine samples collected from five individuals with an independent reference method.

Mesoporous (organo) silica decorated with magnetic nanoparticles as a reusable nanoadsorbent for arsenic removal from water samples

Over the last decade, numerous removal methods using solid-supported magnetic nanocomposites have been employed in order to remove arsenic from aqueous solution. In this report, removal of arsenic from aqueous solution by an organo silica, namely, magnetic mobile crystalline material-41 (MCM-41) functionalized by chlorosulphonic acid (MMCM-41-SO3H), was investigated using atomic absorption spectroscopy. The synthesized magnetic mesoporous materials have satisfactory As (V) adsorption capacity. Linearity for arsenic was observed in the concentration range of 5-100 ppb. In addition, the coefficient of determination (R2) was more than 0.999 and the limit of detection (LOD) was 0.061 ppb. Considering these results, MMCM-41-SO3H has a great potential for the removal of As (V) contaminants and potentially for the application in large-scale wastewater treatment plants.

Chemical generation of arsane and methylarsanes with amine boranes. Potentialities for nonchromatographic speciation of arsenic

The efficiency of chemical generation of arsanes from inorganic arsenic, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), to arsane, AsH3, monomethylarsane, CH3AsH2 (MMA), and dimethylarsane, (CH3)2AsH (DMA), has been investigated in different reaction media with the aim to better elucidate the mechanisms controlling their generation process and to find the experimental conditions to implement a nonchromatographic arsenic speciation analytical method, which is based on the selective determination of some arsenic species. Studies were performed by continuous flow hydride generation coupled with atomic spectrometry (CF-HG-AS), using different reductants such as borane-ammonia (AB), borane-tert-butylamine (TBAB), and sodium tetrahydridoborate (THB) in HCl and HClO4 media, in the presence or absence of L-cysteine (Cys). The efficiency of HG processes for MMA and DMA is mainly controlled by the reactivity of the substrates with the borane, which could be strongly influenced by the formation of ion couples. The protonation of arsane did not play a significant role in the employed reaction system. By taking advantage of the different reactivity pattern of As species in selected generation conditions, DMAA and MMAA could be selectively determined in 0.5 and 10 M HClO4 solutions, respectively, in the presence of Cys, with AB as the reducing agent. The presence of Cys as a masking agent and the peculiar reducing properties of AB ensured a good control of interferences, as far as it has been observed for Co(II), Ni(II), Cu(II), Fe(II), Fe(III). The overall time needed to complete the prereduction step has been verified for MMAA and DMAA at different acidities in order to achieve the best selectivity. The selective determination of DMAA with AB/Cys in HClO4 has been optimized and applied to certified reference materials (CRMs) of natural waters CASS-4, SLRS-4, and NASS-4 (NRCC). The estimation of DMAA concentration allows us to correct the concentration of As(III) for the interference of DMAA in the selective determination of As(III) according to a selective HG method recently reported.

Speciation without chromatography using selective hydride generation: inorganic arsenic in rice and samples of marine origin

Because of the toxicity of inorganic arsenic (iAs), only iAs needs to be monitored in food and feedstuff. This demands the development of easy and quick analytical methods to screen large number of samples. This work focuses on hydride generation (HG) coupled with an ICPMS as an arsenic detector where the HG is added as a selective step to determine iAs in the gaseous phase while organically bound As remains in the solution. iAs forms volatile arsine species with high efficiency when treated with NaBH4 at acidic conditions, whereas most other organoarsenic compounds do not form any or only less volatile arsines. Additionally, using high concentrations of HCl further reduces the production of the less volatile arsines and iAs is almost exclusively formed, therefore enabling to measure iAs without a prior step of species separation using chromatography. Here, we coupled a commercially available HG system to an ICPMS and optimized for determination of iAs in rice and samples of marine origin using different acid concentrations, wet and dry plasma conditions, and different reaction gas modes. Comparing this method to conventional HPLC-ICPMS, no statistical difference in iAs concentration was found and comparable limits of detections were achieved using less than half the instrument time.

Speciation of arsenic (III) and arsenic (V) based on quenching of CdS quantum dots fluorescence using hybrid sequential injection-stopped flow injection gas-diffusion system

A hybrid sequential injection-stopped flow injection system was developed for the speciation of arsenic based on the quenching of mercaptoacetic acid capped cadmium sulfide quantum dots (CdS-MAA QDs) fluorescence intensity. The analytical procedure involves the generation of arsine from As(III) by sodium borohydride in acetate buffer medium pH 6.0. The generated arsine (donor stream) diffuses across the PTFE membrane of the gas-diffusion unit into an acceptor stream and then interacts with CdS-MAA QDs. Total arsenic was determined after pre-reduction of As(V) to As(III) with 1% (m/v) mercaptoacetic acid. Concentration of As(V) in the sample solutions can be deduced from the difference of total arsenic and As(III). Optimization of the experimental conditions and instrumental parameters were investigated. Under optimal conditions, limits of detection were 20 μg L(-1) for As(III) and 40 μg L(-1) for As(V). Recoveries in the range 84-103% were obtained from sediment sample.

Mechanisms of chemical generation of volatile hydrides for trace element determination (IUPAC Technical Report)

Aqueous-phase chemical generation of volatile hydrides (CHG) by derivatization with borane complexes is one of the most powerful and widely employed methods for determination and speciation analysis of trace and ultratrace elements (viz. Ge, Sn, Pb, As, Sb, Bi, Se, Te, Hg, Cd, and, more recently, several transition and noble metals) when coupled with atomic and mass spectrometric detection techniques. Analytical CHG is still dominated by erroneous concepts, which have been disseminated and consolidated within the analytical scientific community over the course of many years. The overall approach to CHG has thus remained completely empirical, which hinders possibilities for further development. This report is focused on the rationalization and clarification of fundamental aspects related to CHG: (i) mechanism of hydrolysis of borane complexes; (ii) mechanism of hydrogen transfer from the borane complex to the analytical substrate; (iii) mechanisms through which the different chemical reaction conditions control the CHG process; and (iv) mechanism of action of chemical additives and foreign species. Enhanced comprehension of these different mechanisms and their mutual influence can be achieved in light of the present state of knowledge. This provides the tools to explain the reactivity of a CHG system and contributes to the clarification of several controversial aspects and the elimination of erroneous concepts in CHG.

A critical investigation of hydride generation-based arsenic speciation in sulfidic waters

In sulfidic environments, hydride generation-based approaches are not suitable for arsenic determination because thioarsenates which can constitute the predominant arsenic species under these conditions (> 80% of total arsenic) are completely ignored. Sample acidification for preservation or during hydride generation leads to loss of total inorganic arsenic due to precipitation of arsenic-sulfur phases. Total concentrations can be determined correctly using 1% potassium iodide as prereducing agent while with L-cysteine (0.16 mol L(-1)), transformation of tetra-, tri-, and dithioarsenate to arsenite remains incomplete. By decreasing the original sample pH, hydride generation destroys thioarsenate species distribution because only monothioarsenate is stable over the whole pH range. Dithioarsenate transforms to arsenite below pH 4. Tetrathioarsenate transforms to trithioarsenate (pH 11.9) which subsequently transforms to arsenite (pH 5.6), followed by precipitation of arsenic-sulfur phases below pH 5. It is thus impossible to determine thioarsenates by hydride generation. The "As(III)"--fraction contains tetra-, tri-, and some dithioarsenate as well as arsenite, while monothioarsenate is determined with arsenate as "As(V)". Different analytical setups have substantial impact on thioarsenate hydride-generation behavior, thus provide little comparability and render reinterpretation of existing arsenic hydride-generation speciation data from sulfidic environments impossible. In natural geothermal water samples from Yellowstone National Park, total arsenic concentrations determined by ICP-MS and by HG-AFS with prereductant agreed well (< 6% relative difference). Speciation results deviated from the behavior predicted for thioarsenates from laboratory experiments, probably due to matrix effects.

Influence of EDTA, carboxylic acids, amino- and hydroxocarboxylic acids and monosaccharides on the generation of arsines in hydride generation atomic absorption spectrometry

The influence of EDTA, carboxylic acids, amino-and hydroxocarboxylic acids, monosaccharides and humic substances on the generation of arsines in hydride generation atomic absorption spectrometry (HGAAS) was investigated. EDTA (0.02 mol L−1), ascorbic acid (0.02 mol L−1) and glucose or fructose (0.2 mol L−1) are useful additives for levelling sensitivities for As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA). The presence of glycine, malonic, tartaric acids, BICIN and soil humin extracts leads to differences in analytical signal response between these arsenic species. An analytical application to the determination of the sum of As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA) as well as the sum of toxicologically relevant hydride forming arsenic fraction As(III) + As(V) + MMA + DMA in EDTA soil/sediment extracts using continuous flow HGAAS was demonstrated. The limit of detection was 0.2 mg kg−1 As. Within-day and between-day precision were in the range 3–7% and 4–10%, respectively, for arsenic contents of 0.7–25 mg kg−1, with recoveries 95–103%.

On-line pre-reduction of pentavalent arsenicals by thioglycolic acid for speciation analysis by selective hydride generation-cryotrapping-atomic absorption spectrometry

An improvement of current method of selective hydride generation based on pre-reduction for differentiation of tri- and pentavalent arsenicals is described, applied for the oxidation state specific speciation analysis of inorganic, mono-, di- and trimethylated arsenicals with minimum sample pretreatment using atomic absorption spectrometry with the multiatomizer. The preconcentration and separation of arsine, methylarsine, dimethylarsine and trimethylarsine is then carried out by means of cryotrapping. Presented study shows that 2% (m/v) L-cysteine hydrochloride monohydrate (L-cys) currently used for off-line pre-reduction of pentavalent arsenicals can be substituted with 1% (m/v) thioglycolic acid (TGA). Much faster pre-reduction of pentavalent arsenicals at 25°C with equal sensitivities as in the case of L-cys has been achieved with TGA. A setup for on-line pre-reduction by TGA has been optimized, with the application of segmented flow analysis for suppression of axial dispersion in the pre-reduction coil. Standard calibrations measured with or without on-line pre-reduction indicate uniform and equal sensitivities for all As forms. The possibility of standardization by water standards of single species (e.g. iAs(III)) for quantification of all other As forms in urine is demonstrated in the recovery study. Limits of detection were 100 ng·l(-1) for iAs(III), 135 ng·l(-1) for iAs(V) and 30 to 50 ng·l(-1) for methylated arsenicals.

Oxidation State Specific Generation of Arsines from Methylated Arsenicals Based on L- Cysteine Treatment in Buffered Media for Speciation Analysis by Hydride Generation - Automated Cryotrapping - Gas Chromatography-Atomic Absorption Spectrometry with the Multiatomizer

An automated system for hydride generation - cryotrapping- gas chromatography - atomic absorption spectrometry with the multiatomizer is described. Arsines are preconcentrated and separated in a Chromosorb filled U-tube. An automated cryotrapping unit, employing nitrogen gas formed upon heating in the detection phase for the displacement of the cooling liquid nitrogen, has been developed. The conditions for separation of arsines in a Chromosorb filled U-tube have been optimized. A complete separation of signals from arsine, methylarsine, dimethylarsine, and trimethylarsine has been achieved within a 60 s reading window. The limits of detection for methylated arsenicals tested were 4 ng l(-1). Selective hydride generation is applied for the oxidation state specific speciation analysis of inorganic and methylated arsenicals. The arsines are generated either exclusively from trivalent or from both tri- and pentavalent inorganic and methylated arsenicals depending on the presence of L-cysteine as a prereductant and/or reaction modifier. A TRIS buffer reaction medium is proposed to overcome narrow optimum concentration range observed for the L-cysteine modified reaction in HCl medium. The system provides uniform peak area sensitivity for all As species. Consequently, the calibration with a single form of As is possible. This method permits a high-throughput speciation analysis of metabolites of inorganic arsenic in relatively complex biological matrices such as cell culture systems without sample pretreatment, thus preserving the distribution of tri- and pentavalent species.

Chemical Vapor Generation of Arsane in the Presence of l-Cysteine. Mechanistic Studies and Their Analytical Feedback

The complex reactivity of the system As-AH-RSH-THB (As=As(III), As(V); AH=HCl, HClO4, CH3COOH; RSH=L-cysteine (Cys); THB=NaBH4) was investigated using continuous flow (CF) hydride generation (HG) coupled either with atomic absorption (AAS) or atomic fluorescence spectrometry (AFS). AsH3 generation was examined in the presence of Cys by varying acidity and the type of acid, the mixing sequence, and the reaction time of reagents. The strong depression of arsane generation, which is typically observed in the range of acidity of 0.2-2 M HCl, can be addressed to the low reaction rate of thiol-borane, hydroboron complexes, or both toward those As(III) substrates that are formed in the same reaction environment. The simultaneous presence of Cys-borane and As(III)-Cys species is at the origin of the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. The selective formation of Cys-borane complexes, which are formed faster than As(III)-thiol complexes, can be achieved by a careful choice of the mixing sequence of the reagents. The simultaneous mixing of sample, Cys, and THB is able to reduce substantially the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. These properties were employed to implement a simple method for selective determination of As(III) in samples containing inorganic arsenic: (i) Total inorganic arsenic is determined by sample treatment with 0.2 M Cys for 30 min, acidity 0.1 M HCl, followed by CF-HG-AFS; (ii) As(III) is selectively determined in 0.005 M CH3COOH in the presence of Cys using a chemifold setup allowing the simultaneous mixing of sample, 0.2 M Cys and 0.1 M THB. The selectivity, measured from the ratio between the slopes of calibration graphs As(III)/As(V), is 220. The interference effects of Cu(II), Fe(III), Ni(II), Co(II), Ag(I), Pd(II), and Pt(IV) can be kept under control using the simultaneous mixing of all the reagents. The tolerance toward the interferences was almost the same as that obtained by allowing the formation of As(III)-Cys complexes (offline sample pretreatment with Cys for 30 min). The method was tested with the application to the natural waters and mineral well waters analysis employing CF-HG-AFS.

Identification of Sb(V) Complexes in Biological and Food Matrixes and Their Stibine Formation Efficiency during Hydride Generation with ICPMS Detection

Several studies have described the synthetic preparation of Sb(V) complexes with organic ligands, but only recently was such a complex identified to exist in beverages stored in PET containers. In the present study, we have investigated by using HPLC-ICPMS and HPLC-ES-MS(/MS), the formation of Sb(V) complexes in various biological (urine) and food matrixes (yoghurt and juice) spiked with noncomplexed inorganic Sb(V). Our results show that Sb(V) complex formation is matrix dependent and that several Sb(V) complexes form to a considerable extent in these matrixes. The results also suggest that the existence of Sb(V) complexes in natural samples may have previously been overlooked due to analytical method limitations, mainly chromatographic, but also detection limitations when hydride generation is used. To overcome some of these limitations, we have developed chromatographic methods suitable for preserving Sb-organic ligand complexes during their separation. When applying this mild nondestructive chromatographic method, we were able to identify novel Sb complexes in yoghurt spiked with inorganic Sb(V), i.e., 1:1 Sb(V)-citrate, 1:1 Sb(V)-lactate, 1:2 Sb(V)-lactate, and other Sb(V)-lactate complexes. This is the first characterization of Sb(V)-lactate complexes. Detailed studies on the hydride generation (HG) efficiency of Sb(V) complexes showed that Sb(V) complexes of high stability, such as Sb(V)-citrate, Sb(V)-(adenosine)n and Sb(V)-(lactate)n (n = 1 or 2), are nondetectable by HG-ICPMS. Furthermore, Sb(V) complexes formed in natural biological and food matrixes were only partly detectable by HG-ICPMS, confirming limitations of analytical methods based on HG volatilization and subsequent stibine detection in natural samples containing complexing ligands with affinity toward Sb(V).

Role of hydroboron intermediates in the mechanism of chemical vapor generation in strongly acidic media

Unknown and controversial aspects related to the mechanisms of hydrolysis of borane complexes and to the mechanisms of chemical vapor generation for trace element determination in strongly acidic media (0.01-10 M HCl) have been investigated and clarified. The overall hydrolysis rates of borane complexes (BH(4)(-), H(3)N-BH(3)) in the acidity range of 0.2-10 M HCl were several orders of magnitude lower than those predicted by kinetics laws and obtained in the pH range of 3.8-14. The decomposition of the borane complexes takes place stepwise and proceeds through the formation of hydroboron intermediates, L(x)()BH(4)(-)(x)()(n)() (x = 1, 2, 3), where L could be one or more species among the donor groups H(2)O, NH(3), OH(-), and Cl(-) and n is the charge of the hydroboron species (n = 0, +1, -1, depending on L). Some intermediates present surprisingly long lifetimes at elevated acidities and play a key role in determining both the overall hydrolysis rates of borane complexes and the reactivity of Hg(II), As(III), Sb(III), Bi(III), Se(IV), Te(IV), and Sn(IV) in chemical vapor generation for trace element determination. Atomic absorption experiments demonstrated that almost all trihydroboron species (LBH(3)(n)()), dihydroboron species (L(2)BH(2)(n)()), and monohydroboron species (L(3)BH(n)()) play an active role in the generation of elemental mercury and stibine. Some of these intermediates are inactive or play a marginal role in the generation of arsine, bismuthine, and hydrogen selenide. Hydrogen telluride is preferentially formed by those hydroboron species, which are stable in strongly acidic conditions, while the same species are unreactive in the generation of stannane. The collected experimental evidence is in agreement with the general reactivity of the elements in chemical vapor generation techniques and, together with other literature data, definitely rule out the hypothesis of "nascent hydrogen" as a possible mechanism of chemical vapor generation by borane complex derivatization.

Mechanism of volatile hydride formation and their atomization in hydride generation atomic absorption spectrometry

The mechanism of volatile hydride generation (HG) and the formation of analyte atoms in the quartz cell atomizer used in the determination of hydride-forming elements (As, Bi, Ge, Pb, Sb, Sn, Te etc.) by atomic absorption spectrometry (AAS), have been critically reviewed. The nascent hydrogen mechanism failed to explain hydride generation under different experimental conditions when tetrahydroborate (THB), amineboreanes (AB) and cyanotrihydroborate (CBH) were used as reductants. Various experimental evidence suggested a non-nascent hydrogen mechanism, in which the transfer of hydrogen directly bonded to boron to an analyte takes place. In electrochemical hydride generation (EcHG), the reduction of the analyte species and subsequent hydrogenation was proposed. The mechanism of analyte atom formation in a quartz tube atomizer has been explained by the following hypotheses: thermal decomposition, oxidation by 02 and collisions by hydrogen free radicals. The free-radical mechanism satisfactorily explains most of the analytical implications. The significant variation in the experimental conditions required to generate different analyte hydrides makes it difficult to arrive at a generalized mechanism of hydride formation.

Arsenic speciation analysis in water samples: a review of the hyphenated techniques

Interests in the determination of different arsenic species in natural waters is caused by the fact that toxic effects of arsenic are connected with its chemical forms and oxidation states. In determinations of water samples inorganic arsenate (As(III), As(V)), methylated metabolities (MMAA, DMAA) and other organic forms such as AsB, AsC, arsenosugars or arsenic containing lipids have the most importance. This article provides information about occurrence of the dominant arsenic forms in various water environments. The main factors controlling arsenic speciation in water are described. The quantification of species is difficult because the concentrations of different forms in water samples are relatively low compared to the detection limits of the available analytical techniques. Several hyphenated methods used in arsenic speciation analysis are described. Specific advantages and disadvantages of methods can define their application for a particular sample analysis. Insufficient selectivity and sensitivity of arsenic speciation methods cause searching for a new or modifications already existing techniques. Some aspects of improvement and modifications of the methods are highlighted.

Dynamic arsenic removal on a MnO2-loaded resin

Previous batch studies on a polystyrene matrix loaded with manganese dioxide, synthesized from an anionic commercial resin in chloride form, have proven the efficiency of this sorbent in As(V) and As(III) removal. This solid is now tested with column experiments to predict its behavior in a treatment process. An artificial water, with a composition in major ions similar to that of granitic water, often contaminated with arsenic, was prepared. This artificial water was used to simulate arsenic removal processes under near-natural conditions and with a stable composition. Furthermore, the hydride generation AAS analytical method was optimized to measure low arsenic concentrations (1 to 20 microg/L).

Determination of arsenic species: A critical review of methods and applications, 2000–2003

We review recent research in the field of arsenic speciation analysis with the emphasis on significant advances, novel applications and current uncertainties.

Flow Injection Analysis of an Ultratrace Amount of Arsenite Using a Prussian Blue-Modified Screen-Printed Electrode

We report here a new electrochemical method for the selective detection of ultratrace amount of arsenite (AsO(2)(-), As(3+)) using a Prussian blue-modified screen-printed electrode (designated as PBSPE) by flow injection analysis (FIA) in 0.1 M, pH 4 KCl/HCl carrier solution. The Prussian yellow/Prussian blue redox couple of the PBSPE was found to mediate the As(3+) oxidation. Various factors influencing the determination of As(3+) were thoroughly investigated in this study. Under the optimized FIA conditions, a linear calibration plot in the range of 50 nM-300 microM with a detection limit (S/N = 3) of 25 nM (i.e., 64.9 pg in 20-microL loop) was observed at an operation potential of +0.6 V vs Ag/AgCl. The sensitivity was good enough to detect arsenite at levels lower than the current EPA standard. This modified electrode showed good resistance to interference from common ions, especially Cl(-), which is generally considered as a major interference in the determination of As(3+) by ICPMS. The practical utility of the PBSPE to detect As(3+) was demonstrated in "blackfoot" disease endemic village groundwater from the southwestern coast area of Taiwan (Pei-Men).