Improvement in arsenic speciation,using hydride generation and atomic absorption spectrophotometry

Improvements in arsenic speciation in sea-water using hydride generation, cold trapping and AAS are reported. Progressive addition of sodium tetrahydroborate and pH optimization are essential to obtain reliable results. The response factor for As^III, As^v, methylarsonic acid and dimethylarsinic acid is nearly the same when sulphuric acid is used for the hydride generation step.     

Solvent bar microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic arsenic in water samples

A new method of solvent bar microextraction (SBME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the speciation of As(III) and As(V) in water samples was developed. The method is based on the chelation of As(III) and ammonium pyrrolidine dithiocarbamate (APDC) under the selected conditions, and the As(III)-PDC complex could be extracted into the organic phase, while As(V) remained in aqueous solution. The post-extraction organic phase was directly injected into ETV-ICP-MS for determination of As(III) with the use of iridium as permanent chemical modifier. As(V) was reduced to As(III) by L-cysteine and was then subjected to SBME prior to total As determination. The assay of As(V) was based on subtracting As(III) from total As. The factors affecting on the SBME, such as organic solvent, sample pH, chelating reagent concentration, stirring rate and extraction time, and chemical modification of iridium in ETV-ICP-MS have been studied. Under the optimized conditions, the enrichment factor of 220-fold could be achieved in 15 min extraction, the limit of detection (LOD) for As(III) was 0.32 pg mL^− 1, and the relative standard deviation (RSD) was 8.8% (0.1 ng mL^− 1, n = 9). Compared with hollow fiber liquid phase microextraction (HF-LPME), SBME has a higher enrichment factor and faster extraction kinetics. In order to validate the accuracy of the method, a Certified Reference Material of GSBZ50004-88 (No. 200420) water sample was analyzed and the results obtained were in good agreement with the certified values. The developed method was also applied to the speciation of inorganic As in environmental waters with satisfactory results.     

Hydride-trapping techniques for the speciation of arsenic

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

HPLC-ICP-MS测定植物样品中6种砷形态化合物

通过优化色谱分离、样品前处理条件,同时对比了电感耦合等离子体质谱的标准模式(STD)、碰撞模式(KED)、氧气反应模式(Oxygen-DRC)、甲烷反应模式(Methane-DRC)的检测结果,建立了一种有效分离植物样品中砷甜菜碱(AsB)、二甲基砷酸(DMA)、亚砷酸(As(Ⅲ))、砷胆碱(AsC)、一甲基砷酸(MM...     

Uranium determination in water samples with elevated salinity from Southern Poland by micro coprecipitation using alpha spectrometry

Due to the importance of water in human life, its quality must be strictly controlled; so simple and reliable analytical methods must be available. For this purpose a rapid procedure for the determination of uranium isotopes in natural water samples with elevated salinity was adopted. It was tested in 16 water samples from Upper and Lower Silesia Regions in Poland. Water samples had salinity in a range of 290–26,925 mg l^{− 1}.In water samples the concentrations of ²³⁴U and ²³⁸U ranged from 2.07 to 52.08 mBq l^{– 1} and from 2.18 to 43.38 mBq l^{– 1} respectively, while ²³⁵U level was below MDA (0.7 mBq l^{− 1}).The isotopic ratio of ²³⁴U/²³⁸U varies in the range from 0.949 to 3.344 in all investigated waters which means that there is usually no radioactive equilibrium between the parent nuclide ²³⁸U and its daughter product ²³⁴U.These results do not show a correlation between total dissolved solids (TDS) values and concentration of dissolved uranium isotopes.Committed effective dose for adults due to uranium intake as a result of drinking water usage was in range of 0.15–3.29 µSv y^{− 1} with an average value of 1.09 µSv y^{− 1} far below the 100 µSv y^{− 1} WHO recommendation.     

Carrier element-free coprecipitation (CEFC) method for the separation, preconcentration and speciation of chromium using an isatin derivative

A new, simple, rapid and sensitive separation, preconcentration and speciation procedure for chromium in environmental liquid and solid samples has been established. The present speciation procedure for Cr(III) and Cr(VI) is based on combination of carrier element-free coprecipitation (CEFC) and flame atomic absorption spectrometric (FAAS) determinations. In this method a newly synthesized organic coprecipitant, 5-chloro-3-[4-(trifluoromethoxy) phenylimino]indolin-2-one (CFMEPI), was used without adding any carrier element for coprecipitation of chromium(III). After reduction of chromium(VI) by concentrated H₂SO₄ and ethanol, the procedure was applied for the determination of total chromium. Chromium(VI) was calculated as the difference between the amount of total chromium and chromium(III). The optimum conditions for coprecipitation and speciation processes were investigated on several commonly tested experimental parameters, such as pH of the solution, amount of coprecipitant, sample volume, etc. No considerable interference was observed from the other investigated anions and cations, which may be found in natural water samples. The preconcentration factor was found to be 40. The detection limit for chromium(III) corresponding to three times the standard deviation of the blank (N = 10) was found 0.7 μg L⁻¹. The present procedure was successfully applied for speciation of chromium in several liquid and solid environmental samples. In order to support the accuracy of the method, the certified reference materials (CRM-TMDW-500 Drinking Water and CRM-SA-C Sandy Soil C) were analyzed, and standard APDC-MIBK liquid-liquid extraction method was performed. The results obtained were in good agreement with the certified values.     

Differential pulse cathodic stripping voltammetric speciation of trace level inorganic arsenic compounds in natural water samples

A simple, fast and sensitive speciation method is described for inorganic arsenic in water at the μg/l level, applicable in the laboratory and in the field, based on differential pulse cathodic stripping voltammetry (DPCSV). Only As(III) is deposited on a Hg electrode in the presence of Cu and Se in HCl medium. Determination of total As is performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference. The detection limit (S/N>3) was 0.5 μg/l with a linear range from 4.5 to 180 μg/l. The relative standard deviation (n=6) was 2.4, 2.5, 4.2% for As(III) and 8.0, 6.8, 9.0% for As(V) at levels of 45, 10, and 5 μg/l, respectively. Analysis of the NIST 1640 natural water standard yielded total arsenic concentration 26.5±3.4 μg/l (n=3) compared to the certified value of 26.7 μg/l. Results obtained on several natural water samples analyzed both in the laboratory and on-site compared well with those obtained by HR ICP-MS, GFAAS and IC-AFS. Ions (phosphate, iron, manganese) commonly found in groundwater containing arsenic were found to have negligible interference.     

Capillary electrophoresis for the speciation of arsenic

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

Speciation and instrumental neutron activation analysis for arsenic in water samples

Ground water samples obtained from West Bengal, India were analyzed for total arsenic and its inorganic species contents by instrumental neutron activation analysis (INAA). Two anion exchange separation methods using Dowex 1X8 in chloride and acetate forms were standardized for the speciation of As(III) and As(V) using radiotracers. The method by Dowex 1X8 in the acetate form was validated using synthetic mixtures of As(III) and As(V), and applied to water samples; the species concentrations were determined by INAA. The accuracy of the INAA method was evaluated by analyzing the NRCC CRM DORM-2 for total arsenic.     

Development of a method for speciation of inorganic arsenic in waters using solid phase extraction and electrothermal atomic absorption spectrometry

A solid phase extraction (SPE) procedure based on Amberlite IRA 900 resin was developed for speciation and separation of inorganic arsenic species (III, V) and total As in water samples. The As species and total As in eluent solutions were determined by electrothermal atomic absorption spectrometry (ETAAS) using Ni chemical modifier with 1200°C pyrolysis temperature. Experimental parameters such as pH value, sample volume, flow rate, volume and concentration of eluent solution for As(V) were optimised and 98.0 ± 1.9% recovery was found at pH 4.0. Experimental adsorption capacity of the resin for As(V) was investigated and 229.9 mg g^–1 was found. Under optimised experimental conditions, instrumental parameters such as limit of detection (LOD) and limit of quantification (LOQ) found were 0.126 and 0.420 µg L^–1, respectively. Interference effects of coexisting ions in the sample matrix on the recovery of As(V) were investigated. Concentration of As(III) was obtained by subtracting As(V) concentration found at pH 4.0 from total As(III + V) found at pH 8.0. The accuracy of the method proposed by using the resin was tested for analysing As species in a waste water standard reference material (SRM, CWW-TM-D) and spiked real water samples with recovery above 95%. The method proposed was also applied to the determinations of As species and total As in underground hot waters and tap water with relative error below 3%.     

Inorganic arsenic speciation analysis of water samples by trapping arsine on tungsten coil for atomic fluorescence spectrometric determination

Arsine trapping on resistively heated tungsten coil was investigated and an analytical method for ultratrace arsenic determination in environmental samples was established. Several chemical modifiers, including Re, Pt, Mo, Ta and Rh, were explored as permanent chemical modifiers for tungsten coil on-line trapping and Rh gave the best performance. Arsine was on-line trapped on Rh-coated tungsten coil at 640 °C, then released at 1930 °C and subsequently delivered to an atomic fluorescence spectrometer (AFS) by a mixture of Ar and H₂ for measurement. In the medium of 2% (v/v) HCl and 3% (m/v) KBH₄, arsine can be selectively generated from As(III). Total inorganic arsenic was determined after pre-reduction of As(V) to As(III) in 0.5% (m/v) thiourea-0.5% (m/v) ascorbic acid solution. The concentration of As(V) was calculated by difference between the total inorganic arsenic and As(III), and inorganic arsenic speciation was thus achieved. With 8 min on-line trapping, the limit of detection was 10 ng L⁻¹ for As(III) and 9 ng L⁻¹ for total As; and the precision was found to be <5% R.S.D. (n = 7) for 0.2 ng mL⁻¹ As. The proposed method was successfully applied in total arsenic determination of several standard reference materials and inorganic arsenic speciation analysis of nature water samples.     

Comparison of three multivariate calibration methods as an approach to arsenic speciation by HG-AAS

This paper compares three multivariate calibration methods, namely classical least squares (CLS), inverse least squares (ILS) and Kaiman filter, applied to continuous-flow hydride generation with sodium tetrahydroborate(III) reducing agent and AAS detection for the purposes of speciation of As(III), As(V), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). The precision of the three multivariate methods was compared in the calibration and prediction steps by standard error of prediction (SEP) and relative error of prediction (REP), respectively, for each analyte and no significant differences have been found for As(III), As(V), MMA, and DMA when the F-test was applied to compare the three multivariate calibration methods in pairs at the 95% confidence level. Determination of the As species was carried out in spiked drinking and sea water in the range 7–35 g 1^–1. Recoveries were in all cases around 100% and the detection limit for the least sensitive species was close to 5 g 1^–1.     

Mercury speciation in environmental solid samples using thermal release technique with atomic absorption detection

A sensitive and very simple method for determination of mercury species in solid samples has been developed involving thermal release analysis in combination with atomic absorption (AAS) detection. The method allows determination of mercury(II) chloride, methylmercury and mercury sulfide at the level of 0.70, 0.35 and 0.20 ng with a reproducibility of the results of 14, 25 and 18%, respectively. The accuracy of the developed assay has been estimated using certified reference materials and by comparison of the results with those of an independent method. The method has been applied for Hg species determination in original samples of lake sediments and plankton.     

Seasonal changes in arsenic speciation in Fucus species

Arsenic speciation in a brown alga, Fucus gardneri, collected in Vancouver, B.C., Canada, was carried out by using high-performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC–ICP–MS). Hydride generation–atomic absorption spectrometry (HG–AAS) was used for total arsenic determination. The relative amounts of some arsenosugars 1 in growing tips are found to be different in comparison with the remainder of the plant. Fucus samples collected in summer contain 9 ppm of total arsenic. Most of the arsenic species are extractable. Fucus samples collected in winter contain relatively higher amounts of arsenic, 16–22 ppm, but only low amounts of this are extractable. © 1998 John Wiley & Sons, Ltd.     

Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode

The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2 nM As(III) at pH 8 and 0.3 nM combined arsenic (III + V) at pH 1 with a 30 s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.     

Ion chromatography–inductively coupled plasma mass spectrometry determination of arsenic species in marine samples

Arsenic speciation analysis in marine samples was performed using ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP‐MS) detection. The separation of eight arsenic species, viz. arsenite, monomethyl arsonic acid, dimethylarsinic acid, arsenate, arsenobetaine, tetramethylarsine oxide, arsenocholine and tetramethylarsonium ion was achieved on a Dionex AS4A (weaker anion exchange column) by using a nitric acid pH gradient eluent (pH 3.3 to 1.3). The entire separation was accomplished in 12 min. The detection limits for the eight arsenic species by IC–ICP‐MS were in the range 0.03–1.6 µ g l^?1, based on 3σ of the blank response (n = 6). The repeatability and day‐to‐day reproducibility were calculated to be less than 10% (residual standard deviation) for all eight species. The method was validated by analyzing a certified reference material (DORM‐2, dogfish muscle) and then successfully applied to several marine samples, e.g. oyster, fish muscle, shrimp and marine algae. The low power microwave digestion was employed for the extraction of arsenic from seafood products. Copyright © 2004 John Wiley & Sons, Ltd.     

Evaluation of atomic fluorescence spectrometry as a sensitive detection technique for arsenic speciation

The potential of coupling anion-exchange high-performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) for arsenic speciation is considered. The effects of hydrochloric acid and sodium tetrahydroborate concentrations on signal-to-background ratio, as well as argon and hydrogen flow rates, were investigated. Detection limits for arsenite, dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate were 0.17, 0.45, 0.30 and 0.38 μg l⁻¹, respectively, using a 20-μl loop. Linearity ranges were 0.1–500 ng for As(III) and MMA (as arsenic), and 0.1–800 ng for DMA and As(V) (as arsenic). Arsenobetaine (AsB) was also determined by introducing an on-line photo-oxidation step after the chromatographic separation. In this case the limits of detection and linear ranges for the different species studied were similar to the values obtained previously for As(V). The technique was tested with a human urine reference material and a volunteer's sample. © 1998 John Wiley & Sons, Ltd.     

Inorganic and methylmercury speciation in environmental samples

The different strategies for mercury species analysis in environmentally-related samples are reviewed. After consideration of the main different steps involved in the speciation of mercury, such steps are discussed with more extension for mercuric ion and methylmercury. The different approaches for preservation of these mercury species during the storage of samples are considered. Different ways for the extraction of mercury species from the several possible environmental compartments and the possibilities for preconcentration of such species after previous derivatization reactions are discussed. Mercuric ions and methylmercury chromatographic and non-chromatographic separations along with different techniques used for sensitive and selective detection of mercury are also critically reviewed. Ranges of published detection limits achievable for such species determination, by using hyphenated techniques between a chromatographic separation and a specific atomic detector are also given.     

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic.

An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed.

Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min⁻¹ flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g⁻¹), Sargassum (38 ± 2 μg g⁻¹) and Chlorella (9 ± 1 μg g⁻¹) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g⁻¹). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volume.     

Inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology

The paper presents a procedure for the multi-element inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology. Total As(III, V), Se(IV, VI) and Sb(III, V) were determined according to the following procedure: titanium dioxide (TiO₂) was used to adsorb inorganic species of As, Se and Sb in sample solution; after filtration, the solid phase was prepared to be slurry for determination. For As(III), Se(IV) and Sb(III), their inorganic species were coprecipitated with Pb-PDC, dissolved in dilute nitric acid, and then determined. The concentrations of As(V), Se(VI) and Sb(V) can be calculated by the difference of the concentrations obtained by the above determinations. For the determination of As(III), Se(IV) and Sb(III), palladium was chosen as a modifier and pyrolysis temperature was 800 °C. Optimum conditions for the coprecipitation were listed for 100 ml of sample solution: pH 3.0, 15 min of stirring time, 40.0 μg l⁻¹ Pb(NO₃)₂ and 150.0 μg l⁻¹ APDC. The proposed method was applied to the determination of trace amounts of As(III, V), Se(IV, VI) and Sb(III, V) in river water and seawater.