Speciation of Arsenic in Drinking Water by Dispersive Liquid–Liquid Microextraction,Graphite Furnace Atomic Absorption Spectrometry,and Orthogonal Array Design

Orthogonal array design was used to optimize arsenic speciation in drinking water in contact with materials by dispersive liquid–liquid microextraction followed by graphite furnace atomic absorption spectrometry. Arsenic speciation was achieved by the formation of an arsenic(III) hydrophobic complex with a new chelating agent, 1,2,6-hexanetriol trithioglycolate, at neutral pH. The complex was extracted into the organic phase, while arsenic(V) remained in aqueous solution. The concentration of As(V) was determined by subtracting As(III) from the total arsenic following the reduction of As(V) to As(III) by L-cysteine. Orthogonal array design with OA₁₆ (44) and OA₉ (33) matrices was used to optimize the efficiency of dispersive liquid–liquid microextraction and the reduction of As(V) to As(III), respectively. Under the optimal conditions, the detection limit was 0.03?µg?L^?1 for As(III) and the relative standard deviation was 5.9% with an enhancement factor of 87. The calibration curve was linear from 0.19 to 3.0?µg?L^?1 with a correlation coefficient of 0.9996. The developed method was used for arsenic speciation in solutions of drinking water that contacted materials. The recoveries of fortified samples were in an acceptable range from 92.0 to 113.3%.     

Arsenic speciation in natural water samples by coprecipitation-hydride generation atomic absorption spectrometry combination

A speciation procedure for As(III) and As(V) ions in environmental samples has been presented. As(V) was quantitatively recovered on aluminum hydroxide precipitate. After oxidation of As(III) by using dilute KMnO₄, the developed coprecipitation was applied to determination of total arsenic. Arsenic(III) was calculated as the difference between the total arsenic content and As(V) content. The determination of arsenic levels was performed by hydride generation atomic absorption spectrometry (HG-AAS). The analytical conditions for the quantitative recoveries of As(V) including pH, amount of aluminum as carrier element and sample volume, etc. on the presented coprecipitation system were investigated. The effects of some alkaline, earth alkaline, metal ions and also some anions were also examined. Preconcentration factor was calculated as 25. The detection limits (LOD) based on three times sigma of the blank (N: 21) for As(V) was 0.012 μg L⁻¹. The satisfactory results for the analysis of arsenic in NIST SRM 2711 Montana soil and LGC 6010 Hard drinking water certified reference materials for the validation of the method was obtained. The presented procedure was successfully applied to real samples including natural waters for arsenic speciation.     

Hollow fiber liquid phase microextraction combined with electrothermal atomic absorption spectrometry for the speciation of arsenic (III) and arsenic (V) in fresh waters and human hair extracts

A new method of hollow fiber liquid phase microextraction (HF-LPME) using ammonium pyrrolidine dithiocarbamate (APDC) as extractant combined with electrothermal atomic absorption spectrometry (ETAAS) using Pd as permanent modifier has been described for the speciation of As(III) and As(V). In a pH range of 3.0-4.0, the complex of As(III)-APDC complex can be extracted using toluene as the extraction solvent leaving As(V) in the aqueous layer. The post extraction organic phase was directly injected into ETAAS for the determination of As(III). To determine total arsenic in the samples, first As(V) was reduced to As(III) by l-cysteine, and then a microextraction method was performed prior to the determination of total arsenic. As(V) assay was based on subtracting As(III) form the total arsenic. All parameters, such as pH of solution, type of organic solvent, the amount of APDC, stirring rate and extraction time, affecting the separation of As(III) from As(V) and the extraction efficiency of As(III) were investigated, and the optimized extraction conditions were established. Under optimized conditions, a detection limit of 0.12 ng mL⁻¹ with enrichment factor of 78 was achieved. The relative standard deviation (R.S.D.) of the method for five replicate determinations of 5 ng mL⁻¹ As(III) was 8%. The developed method was applied to the speciation of As(III) and As(V) in fresh water and human hair extracts, and the recoveries for the spiked samples are 86-109%. In order to validate the developed method, three certified reference materials such as GBW07601 human hair, BW3209 and BW3210 environmental water were analyzed, and the results obtained were in good agreement with the certified values provided.     

Determination and pharmacokinetic properties of arsenic speciation in Xiao‐Er‐Zhi‐Bao‐Wan by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry

A method of high performance liquid chromatography with a Hamilton PRP‐X100 ion‐exchange column (250 × 4.1 mm id, 10 μm) coupled to inductively coupled plasma mass spectrometry was employed to generate a full concentration–time profile of arsenic speciation after oral administration. The results exhibited good linearity and revealed that, in the pills, the average arsenic concentration was 10105.4 ± 380.7 mg/kg, and in the water extraction solution, the inorganic As(III) and As(V) concentrations were 220.1 ± 12.6 and 45.5 ± 2.3 mg/kg, respectively. No trace of monomethyl arsenic acid was detected in any of the plasma samples. We then successfully applied the established methodology to examine the pharmacokinetics of arsenic speciation. The resulting data revealed that, after oral administration in rats, the plasma concentration of each arsenic species reached C_max shortly after initial dosing, and that the distribution and elimination of As(V) was faster than that of As(III) and dimethyl arsenic acid. Additionally, the t_1/2 values of As(V), As(III), and dimethyl arsenic acid were 3.4 ± 1.6, 14.3 ± 4.0, and 19.9 ± 1.6 h, respectively. This study provides references for the determination of arsenic speciation in mineral‐containing medicines and could serve as a useful tool in measuring the true toxicity in traditional medicines that contain them.     

Determination of inorganic arsenic species As(III) and As(V) by high performance liquid chromatography with hydride generation atomic absorption spectrometry detection

The paper presents the principles and advantages of a technique combining high performance liquid chromatography and hydride generation atomic absorption spectrometry (HPLC-HGAAS) applied to speciation analysis of inorganic species of arsenic As(III) and As(V) in ground water samples. With separation of the arsenic species on an ion-exchange column in the chromatographic system and their detection by the hydride generation atomic absorption spectrometry, the separation of the analytical signals of the arsenic species was excellent at the limits of determination of 1.5 ng/ml As(III) and 2.2 ng/ml As(V) and RSD of 4.3% and 7.8% for the concentration of 25 ng/ml. The hyphenated technique has been applied for determination of arsenic in polluted ground water in the course of the study on migration of micropollutants. For total arsenic concentration two independent methods: HGICP-OES and HGAAS were used for comparison of results of real samples analysis.     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

Optimization of a flow injection system with amperometric detection for arsenic determination.

A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH(4). Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3 sigma) at room temperature was 5 microg/dm(3) of As(III). The relative standard deviation for a 1 mg/dm(3) As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm(3) Sb(III), 5 mg/dm(3) Sn(II), 10 mg/dm(3) Se(IV), 1 mg/dm(3) As(V), 1 mg/dm(3) hydrasine, 1 mg/dm(3) Fe(II) or 0.5 mg/dm(3) Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.     

Selective determination of trace arsenic and antimony species in natural waters by gas chromatography with a photoionization detector

Traces amounts of arsenic and antimony in water samples were determined by gas chromatography with a photoionization detector after liquidnitrogen cold trapping of their hydrides. The sample solution was treated with sodium hydroborate (NaBH₄) under weak-acid conditions for arsenic(III) and antimony(III) determination, and under strong-acid conditions for arsenic(III+V) and antimony(III+V) determination. Large amounts of carbon dioxide (CO₂) and water vapor obscured determination of arsine and stibine. Better separation from interference could be achieved by removing CO₂ and water vapor in two tubes containing sodium hydroxide pellets and calcium chloride, respectively. The detection limits of this method were 1.8 ng dm^?3 for arsenic and 9.4 ng dm^?3 for antimony in the case of 100-cm³ sample volumes. Therefore, it is suitable for determination of trace arsenic and antimony in natural waters.     

Comparison of extraction procedures for arsenic speciation in environmental solid reference materials by high‐performance liquid chromatography–hydride generation‐atomic fluorescence spectroscopy

Water and ‘soft’ extractions (hydroxylammonium hydrochloride, ammonium oxalate and orthophosphoric acid) have been studied and applied to the determination of arsenic species (arsenite, arsenate, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)) in three environmental solid reference materials (river sediment, agricultural soil, sewage sludge) certified for their total arsenic content. The analytical method used was ion exchange liquid chromatography coupled on‐line to atomic fluorescence spectroscopy through hydride generation. Very low detection limits for arsenic were obtained, ranging from 0.02 to 0.04 mg kg^?1 for all species in all matrices studied. Orthophosphoric acid is the best extractant for sediment (mixed origin) and sludge samples (recent origin) but not for the old formation soil sample, from which arsenic is extracted well only by oxalate. Both inorganic forms (As(III) and As(V)) are significant in all samples, As(V) species being predominant. Moreover, organic forms are found in water extracts of all samples and are more important in the sludge sample. These organic forms are also present in the ‘soft’ extracts of sludge. Microwave‐assisted extraction appears to minimize the risk of a redox interconversion of inorganic arsenic forms. This study points out the necessity of combining direct and sequential extraction procedures to allow for initial arsenic speciation and to elucidate the different mineralogical phases–species associations. Copyright © 2002 John Wiley & Sons, Ltd.     

Arsenic species analysis in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry

A novel pretreatment system and method for arsenic species continuous analysis of arsenite, arsenate, monomethylarsenate (MMA) and dimethylarsonate (DMA) in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry (LC-HG-AFS) was designed. Arsenic species of As(III), As(V), MMA and DMA in freshwater samples can be well separated, and the analytical time using the developed method is shortened twice compared to the conventional analytical procedure. Besides, the signal of As(V) can be increased by about 50% and the sensitivity to As(V) has been enhanced. The common coexisting ions in freshwater samples have no interferences with arsenic speciation analysis. A sensitive, low cost and interference-free procedure was developed and successfully applied to arsenic speciation in freshwater with the recoveries of four arsenic species within 89.2–106.2%. LC-HG-AFS has good prospects for speciation analysis of trace and ultra trace elements allowing for hydride generation.     

Speciation of arsenic in a contaminated soil by solvent extraction

Soil collected from a disused cattle dip in northern New South Wales was studied with the aim of developing an inexpensive, yet effective method for quantitative determination of arsenic(III), arsenic(V) and total organic arsenic in a contaminated soil. Hydrochloric acid extractions were used as a method for removal of the arsenic from the soil in a form suitable for speciation. It was found that the extraction efficiency varied with the ratio of soil to acid, and the concentration of the acid. Arsenic(III), as arsenic trichloride, was selectively extracted into chloroform from a solution highly concentrated in hydrochloric acid. This was followed by back-extraction of the arsenic into water. Total inorganic arsenic was determined in a similar manner after the reduction of arsenic(V) to the trivalent state with potassium iodide. Arsenic(V) was determined by the difference between the results for arsenic(III) and total inorganic arsenic. All analyses for the various arsenic species were performed by hydride generation-atomic absorption spectroscopy; concentrations of total arsenic in the soil were confirmed using X-ray fluorescence spectrometry. It was found that all the arsenic in the soil was present as inorganic arsenic in the pentavalent state. This reflects the ability of arsenic to interchange between species, since the original species in cattle dipping solution is arsenic(III).     

Characterization of As (V), As (III) by selective reduction/adsorption on palladium nanoparticles in environmental water samples

Hydrazine (HZ) and sodium borohydride (BH) are commonly used reagents for the production of palladium nanoparticles (PdNP) in aqueous solution and also for the reduction of arsenic from higher oxidation state to lower oxidation state. A methodology based on the quantitative adsorption of reduced arsenic species on PdNP generated in situ by BH and HZ is described to characterize As (V) and As (III) in environmental water samples. It was observed that PdNP obtained by BH gave quantitative recovery of As (V) and (III) and the PdNP obtained by HZ could account for As (III). The reduced palladium particles are collected and dissolved in minimum amount of nitric acid. The quantification of arsenic was carried out using GFAAS. Optimization of the experimental conditions and instrumental parameters were investigated in detail. The proposed procedure was validated by applying it for the determination of the content of total As in Certified Reference Material BND 301-02 (NPL, India). The detection limit of arsenic in environmental water samples was 0.029 μg L⁻¹ with an enrichment factor of 50. The relative standard deviation (R.S.D.) for 10 replicate measurements of 5 μg mL⁻¹ was 4.2%. The proposed method was successfully applied for the determination of sub ppm to ppm levels of arsenic (V), (III) in environmental water samples.     

Ultra-trace arsenic and mercury speciation and determination in blood samples by ionic liquid-based dispersive liquid-liquid microextraction combined with flow injection-hydride generation/cold vapor atomic absorption spectroscopy

A simple, fast, and sensitive method for speciation and determination of As (III, V) and Hg (II, R) in human blood samples based on ionic liquid-dispersive liquid-liquid microextraction (IL-DLLME) and flow injection hydride generation/cold vapor atomic absorption spectrometry (FI-HG/CV-AAS) has been developed. Tetraethylthiuram disulfide, mixed ionic liquids (hydrophobic and hydrophilic ILs) and acetone were used in the DLLME step as the chelating agent, extraction and dispersive solvents, respectively. Using a microwave assisted-UV system, organic mercury (R-Hg) was converted to Hg(II) and total mercury amount was measured in blood samples by the presented method. Total arsenic content was determined by reducing As(V) to As(III) with potassium iodide and ascorbic acid in a hydrochloric acid solution. Finally, As(V) and R-Hg were determined by mathematically subtracting the As(III) and Hg(II) content from the total arsenic and mercury, respectively. Under optimum conditions, linear range and detection limit (3σ) of 0.1–5.0 µg L^?1 and 0.02 µg L^?1 for As(III) and 0.15–8.50 µg L^?1 and 0.03 µg L^?1 for Hg(II) were achieved, respectively, at low RSD values of < 4% (N = 10). The developed method was successfully applied to determine the ultra-trace amounts of arsenic and mercury species in blood samples; the validation of the method was performed using standard reference materials.     

On‐Line Determination of Arsenic Species in Sea Water by Selective Hydride Generation Coupled with Inductively Coupled Plasma — Mass Spectrometry

A method for direct de termination of total in organic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in sea water was developed by combining continuous‐flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP‐MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total in organic arsenic, DMA and As(III) are 6 M HNO₃, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively deter mined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection lim its (as based on 3‐sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. There liability of the pro posed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural sea water samples can be obtained.     

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1 M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1 M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.     

Determination of trace arsenic in hydrofluoric acid by hydride generation and atomic absorption spectrometry

Practical procedures are given for determination of arsenic(III) and (V) in hydrofluoric acid by means of hydride generation and atomic absorption spectrometry. Arsenic(III) can be determined by direct generation of arsine with sodium borohydride in hydrochloric/hydrofluoric acid medium, arsenic(V) being only slightly reduced under the conditions used. For its determination, arsenic(V) has to be prereduced with potassium iodide, and even then its reduction to arsenic(III) and then arsine is far from complete. It is possible to determine it in presence of arsenic(III) by a difference method, but this is recommended only if the As(V)/As(III) ratio is greater than 1. Total arsenic can be determined after oxidation of As(III) and evaporation of most of the hydrofluoric acid. The limit of determination is 5 g/l for arsenic(III) and 0.25 g/l for total arsenic; the relative standard deviation is about 10%.     

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

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

Simultaneous determination of arsenic species and chromium(VI) by high-performance liquid chromatography-inductively coupled plasma-mass spectrometry

The simultaneous determination of As(III), As(V), monomethylarsenic acid (MMA), dimethylarsinic acid (DMA) and Cr(VI) in fresh water has been carried out by coupling an anion-exchange column to an inductively coupled plasma-mass spectrometer. Optimisation of chromatographic conditions led to baseline separation of signals from the five species in approximately 9 min using gradient elution. Detection limits were 0.02-0.05 microg As l(-1) and 5.5 microg Cr l(-1). Repeatability was 2-3% for arsenic species and higher, i.e., 8%, for Cr(VI) due to the higher background for this species. Arsenic species and hexavalent chromium stability in surface water samples was evaluated, and storage conditions were set to 1 day at 4 degrees C in polyethylene flasks (without acidification) in order to avoid As(III)-As(V) conversions. The method was applied to the analysis of surface water.     

Determination of inorganic arsenic in white fish using microwave-assisted alkaline alcoholic sample dissolution and HPLC-ICP-MS

An analytical method for the determination of inorganic arsenic in fish samples using HPLC-ICP-MS has been developed. The fresh homogenised sample was subjected to microwave-assisted dissolution by sodium hydroxide in ethanol, which dissolved the sample and quantitatively oxidised arsenite (As(III)) to arsenate (As(V)). This allowed for the determination of inorganic arsenic as a single species, i.e. As(V), by anion-exchange HPLC-ICP-MS. The completeness of the oxidation was verified by recovery of As(V) which was added to the samples as As(III) prior to the dissolution procedure. The full recovery of As(V) at 104±7% (n=5) indicated good analytical accuracy. The uncertified inorganic arsenic content in the certified reference material TORT-2 was 0.186±0.014 ng g^–1 (n=6). The method was employed for the determination of total arsenic and inorganic arsenic in 60 fish samples including salmon from fresh and saline waters and in plaice. The majority of the results for inorganic arsenic were lower than the LOD of 3 ng g^–1, which corresponded to less than one per thousand of the total arsenic content in the fish samples. For mackerel, however, the recovery of As(III) was incomplete and the method was not suited for this fat-rich fish.