Speciation Analysis Of Inorganic Arsenic Research Articles

Speciation analysis of inorganic arsenic in natural water by carbon nanofibers separation and inductively coupled plasma mass spectrometry determination

In this paper, carbon nanofibers (CNFs) as a novel solid phase extraction sorbent were developed for speciation preconcentration and separation of inorganic arsenic species As(III) and As(V) prior to determination by inductively coupled plasma mass spectrometry (ICP-MS). It was found that during all the steps of the separation, As(III) was selectively sorbed on the microcolumn packed with CNFs within a pH range of 1.0–3.0 in the presence of ammonium pyrroinedithiocarbamate (APDC), while As(V) was passed through the microcolumn without the retention. Various experimental parameters affecting the separation and determination of As(III) and As(V) have been investigated in detail. Under the optimized conditions, the detection limits of this method for As(III) were 0.0045 ng mL −1 with an enrichment factor of 33 and 0.24 ng mL −1 for As(V), and the relative standard deviations for As(III) and As(V) were 2.6% and 1.9% ( n = 9, c = 1.0 ng mL −1), respectively. In order to verify the accuracy of the method, a certified reference of water sample was analyzed, and the results obtained were in good agreement with the certified values. The proposed method was applied for the analysis of inorganic arsenic species in groundwater and lake water with the recovery of 92–106%.

Separation and preconcentration of inorganic arsenic species in natural water samples with 3-(2-aminoethylamino) propyltrimethoxysilane modified ordered mesoporous silica micro-column and their determination by inductively coupled plasma optical emission spectrometry

A simple and sensitive method using micro-column packed with 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) modified ordered mesoporous silica combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for the speciation of inorganic arsenic (As(III) and As(V)) has been developed. The adsorption behaviors of As(III) and As(V) on AAPTS modified ordered mesoporous silica were investigated. It was found that As(V) can be selectively adsorbed on the micro-column within pH of 3–9, while As(III) could not be retained in the studied pH range and passed through the micro-column directly. Total inorganic arsenic was extracted after the oxidation of As(III) to As(V) with 50.0 μmol L −1 KMnO 4. The assay of As(III) was based on subtracting As(V) from total As. The effect of various parameters on the separation/preconcentration of As(III) and As(V) have been investigated and the optimal experimental conditions were established. The adsorption capacity of AAPTS modified ordered mesoporous silica for As(V) was found to be 10.3 mg g −1. The detection limit of the method for As(V) was 0.05 μg L −1 with an enrichment factor of 100, and the relative standard deviation (R.S.D.) was 5.7% ( n = 7, C = 1.0 μg L −1). In order to validate the developed method, a certified reference material GSBZ50004-88 environmental water sample was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the speciation analysis of inorganic arsenic in natural water samples.

On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l −1 HNO 3. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO 4 (50.0 μmol l −1). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h −1 and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l −1 for As(V) and 0.10 μg l −1 for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l −1 level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l −1 with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.

Speciation analysis of inorganic arsenic in water samples by immobilized nanometer titanium dioxide separation and graphite furnace atomic absorption spectrometric determination

A novel solid phase extraction sorbent, nanometer titanium dioxide immobilized on silica gel (immobilized nanometer TiO 2), was prepared by sol–gel method, and the adsorptive potential of immobilized nanometer TiO 2 for inorganic arsenic species (As(III) and As(V)) was assessed. It was found that both As (III) and As(V) could be adsorbed quantitatively on immobilized TiO 2 within a pH range of 5.0–7.5, and only As(III) could be quantitatively retained on the sorbent within a pH range of 9.5–10.5 while As(V) was passed through the microcolumn without the retention. Based on this fact, a new speciation scheme for inorganic arsenic was established, which involved determining total As at pH 6.0 and As(III) at pH 10, with As(V) obtained by difference. The adsorption capacity of immobilized nanometer TiO 2 for As(III) was found to be 4.22 mg g −1. Under the optimized conditions, the detection limits of this method for As(III) were 24 ng L −1 with an enrichment factor of 50, and the relative standard deviation (R.S.D.%) was 4.8% ( n = 11, c = 5 ng mL −1). The proposed method has been applied to the speciation of inorganic arsenic in natural water samples with satisfactory results.

Speciation analysis of inorganic arsenic by a multisyringe flow injection system with hydride generation–atomic fluorescence spectrometric detection

In this study, a new technique by hydride generation–atomic fluorescence spectrometry (HG–AFS) for determination and speciation of inorganic arsenic using multisyringe flow injection analysis (MSFIA) is reported. The hydride (arsine) was generated by injecting precise known volumes of sample, a reducing sodium tetrahydroborate solution (0.2%), hydrochloric acid (6 M) and a pre-reducing solution (potassium iodide 10% and ascorbic acid 0.2%) to the system using a multisyringe burette coupled with one multi-port selection valve. This solution is used to pre-reduce As(V) to As(III), when the task is to speciate As(III) and As(V). As(V) is determined by the difference between total inorganic arsenic and As(III). The reagents are dispensed into a gas–liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame. Nitrogen has been employed as a drier gas (Fig. 1). Several variables such as sample and reagents volumes, flow rates and reagent concentrations were investigated in detail. A linear calibration graph was obtained for arsenic determination between 0.1 and 3 μg l −1. The detection limit of the proposed technique (3 σ b/S) was 0.05 μg l −1. The relative standard deviation (R.S.D.) of As at 1 μg l −1 was 4.4 % ( n = 15). A sample throughput of 10 samples per hour was achieved. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of As(III) and As(V) by means of the developed technique were obtained.

Speciation analysis of inorganic arsenic by microchip capillary electrophoresis coupled with hydride generation atomic fluorescence spectrometry

A novel method for speciation analysis of inorganic arsenic was developed by on-line hyphenating microchip capillary electrophoresis (chip-CE) with hydride generation atomic fluorescence spectrometry (HG-AFS). Baseline separation of As(III) and As(V) was achieved within 54 s by the chip-CE in a 90 mm long channel at 2500 V using a mixture of 25 mmol l −1 H 3BO 3 and 0.4 mmol l −1 CTAB (pH 8.9) as electrolyte buffer. The precisions (RSD, n = 5) ranged from 1.9 to 1.4% for migration time, 2.1 to 2.7% for peak area, and 1.8 to 2.3% for peak height for the two arsenic species at 3.0 mg l −1 (as As) level. The detection limits (3 σ) for As(III) and As(V) based on peak height measurement were 76 and 112 μg l −1 (as As), respectively. The recoveries of the spikes (1 mg l −1 (as As) of As(III) and As(V)) in four locally collected water samples ranged from 93.7 to 106%.

Determination of (ultra)trace amounts of arsenic(III) and arsenic(V) in water by inductively coupled plasma mass spectrometry coupled with flow injection on-line sorption preconcentration and separation in a knotted reactor.

A method has been developed for determination of (ultra)trace amounts of As(III) and As(V) in water by flow injection on-line sorption preconcentration and separation coupled with inductively coupled plasma mass spectrometry (ICPMS) using a knotted reactor (KR). The determination of As(III) was achieved by selective formation of the As(III)-pyrrolidine dithiocarbamate complex over a sample acidity range of 0.01-0.7 mol L-1 HNO3, its adsorption onto the inner walls of the KR made from 150-cm-long, 0.5-mm-i.d. PTFE tubing, elution with 1 mol L-1 HNO3, and detection by ICPMS. Total inorganic arsenic was determined after prereduction of As(V) to As(III) in a 1% (m/v) L-cysteine-0.03 mol L-1 HNO3 media. The concentration of As(V) was calculated by difference (the total inorganic arsenic and As(III)). Owing to the group-specific character of the chelating agent, and the use of an efficient rinsing step before elution, the interferences encountered in conventional ICPMS from common major matrix, alkali and alkaline earth metals, and chlorides were eliminated. The presence of organoarsenic species such as monomethylarsonate and dimethylarsinate in water samples had no effect on the results of As(III) and As(V). Thus, the method can be applied to the speciation analysis of inorganic arsenic at submicrogram per liter levels in aqueous solutions with high total content of dissolved solid and/or high content of chlorides. Using a preconcentration time of 60 s and a sample flow rate of 5 mL min-1, an enhancement factor of 22 was achieved in comparison with conventional ICPMS. The time required for a single determination was 200 s. The detection limits (3s) was evaluated to be 0.021 microgram L-1 for As(III) and 0.029 microgram L-1 for total inorganic arsenic. The precision for 14 replicate determinations of 1 microgram L-1 As(III) was 2.8% (RSD) with drift correction and 3.9% (RSD) without drift correction. The concentrations of As(III) and As(V) in synthetic mixtures obtained by the present method were in good agreement with expected values. Results obtained by the proposed method for total arsenic in a river water reference material agreed well with certified and recently reevaluated values. The method was also applied to the speciation analysis of inorganic arsenic in porewaters.