Speciation of arsenic in water samples by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry at trace levels using a post-column reaction system

Anion-exchange HPLC has been combined with hydride generation – atomic absorption spectrometry (HG-AAS) for the routine speciation of arsenite, arsenate, monomethylarsenic acid and dimethylarsinic acid. The sensitivity of the AAS-detection was increased by a post-column reaction system to achieve complete formation of volatile arsines from the methylated species and arsenate. The system allows the quantitative determination of 0.5 g/l of each arsenic compound in water samples. The stability of synthetical and natural water containing arsenic at trace levels was investigated. To preserve stored water samples, a method for quantitative separation of arsenate at high pH-values with the basic anion-exchange resin Dowex 1×8 was developed.     

Simultaneous determination of arsenic, selenium and antimony in water by an inductively coupled plasma hydride method

Summary Arsenic, selenium and antimony were determined using on-line hydride generation in conjunction with a simultaneous medium power inductively coupled plasma (ICP) spectrometer with conventional pneumatic nebulization. The sample, acidified with 3 mol/l hydrochloric acid was mixed with 1% (m/v) sodium tetrahydroborate and 5% (m/v) potassium iodide, the mixed stream being pumped to the nebulizer of the ICP spectrometer. Calibration curves were linear up to 1 mg/l analyte, with detection limits of 2; 3 and 3 g/l for arsenic, antimony and selenium, respectively, for 10 s integration times and a sample uptake rate of 2.15 ml/min.     

Arsenic speciation in water samples containing high levels of copper: removal of copper interference affecting arsine generation by continuous flow solid phase chelation

A simple continuous flow method is proposed to eliminate copper interference in arsenic speciation by hydride generation, based on the selective retention of this interfering ion in an iminodiacetate chelating resin previous to the hydride generation process. The arsines generated were cold trapped and measured by ICP/OES. The proposed method allows about 98% of the copper present in the samples to be removed. Minor co-retention of As(V) was observed as a result of electrostatic interaction between the arsenate anion and the nitrogen of the iminodiacetate group of the chelating resin Muromac A-1, the charge distribution of which is modified when copper is chelated. The species As(III), MMA and DMA were not retained in the microcolumn, probably because these species are mainly in the molecular form at the working pH value (4.5). In synthetic samples containing 50 g l^–1 of each arsenic species together with 100 mg l^–1 copper, the recoveries obtained were: As(V) 97.6%, As(III) 100%, MMA 99.8%, and DMA 99.9%. The method was applied to arsenic speciation in river water samples containing high levels of copper.     

Speciation of arsenic in water samples by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry at trace levels using a post-column reaction system

Anion-exchange HPLC has been combined with hydride generation - atomic absorption spectrometry (HG-AAS) for the routine speciation of arsenite, arsenate, monomethylarsenic acid and dimethylarsinic acid. The sensitivity of the AAS-detection was increased by a post-column reaction system to achieve complete formation of volatile arsines from the methylated species and arsenate. The system allows the quantitative determination of 0.5 microg/l of each arsenic compound in water samples. The stability of synthetical and natural water containing arsenic at trace levels was investigated. To preserve stored water samples, a method for quantitative separation of arsenate at high pH-values with the basic anion-exchange resin Dowex 1x8 was developed.     

The use of optical emission spectrometry with microwave induced plasma (MIP) discharges in a surfatron combined to different types of hydride generation for the determination of arsenic

The stability and analytical figures of merit of argon microwave induced plasma (MIP) discharges in a surfatron as sources for optical emission spectrometry (OES) are described. These MIPs have been used for the determination of arsenic after hydride generation. They could cope with the excess of hydrogen developed during the hydride generation step and thus not necessitated an isolation of the hydrides before releasing them into the MIP. Two methods for the generation of the volatile AsH₃ were applied. First a micro method was used with solid NaBH₄ on which 10 1 of the acidified sample solution is transferred. Its capabilities were compared to those of continuous hydride generation using a 5% (w/w) NaBH₄-solution and continuous liquid removal in a flow cell. Both methods were optimized for an argon MIP operated at a power of 120–160 W and gas flows of 20 l/h Ar. In the case of solid NaBH₄ the detection limit for As has been found to be 1.0 g/ml (10 ng) and with the flow cell hydride generation 50 ng/ml. The calibration curves are linear over three orders of magnitude. Interferences caused by Sb, Fe, Sn and NaCl were investigated. No interferences occurred for Sb up to an interferent concentration of 250 g/ml. The presence of Fe causes a significant depression of the As signal whereas an increase of the As signal was observed in the case of Sn. High NaCl concentrations did not influence the As signals when using continuous hydride generation, but had a great influence when using solid NaBH₄.     

Application of the photoionization detector for single determinations of hydride forming elements

The application of a photoionization detector in conjunction with a flow-through system is described for the determination of arsenic, antimony, selenium, tellurium, bismuth, tin, sulfide and ammonia. The analytical procedure is based upon a preliminary generation of the hydride compounds, their subsequent transfer to the gas phase and finally their detection in the photoionization detector. Linear calibration curves were obtained over three to four orders of magnitude with the following 3s-detection limits: 4 ng/ml As, 0.3 ng/ml Sb, 0.5 ng/ml Se, 3.0 ng/ml Te, 0.1 g/ml Bi, 0.5 g/ml Sn, 10.0 ng/ml S^2–, 0.5 g/ml NH₃.     

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.     

Simultaneous determination of arsenic, selenium, and mercury by Ion exchange-vapor generation-inductively coupled plasma-mass spectrometry

Ion exchange (IE)-vapor generation (VG)-inductively coupled plasma (ICP)-mass spectrometry (MS) method has been employed to simultaneously determine trace amounts of As, Se, and Hg in acidic conditions. Before hydride generation, anion-exchange column was used to separate the analytes from the matrix. Effects of sample solution acidity, eluant conditions and concentrating time were investigated and optimized. The method sensitivity was improved, as well as the ability to refrain interference caused by chloride, mental ions and other hydride-forming elements compared with (CF)VG-ICP-MS method. Limits of detection (3σ, n = 10) for As, Se, and Hg were As, 0.0021 ng/ml; Se, 0.0022 ng/ml; Hg, 0.0007 ng/ml, respectively; and recovery values for interference experiments were between 95.6 and 100.3%. The developed method was applied to four standard biological and geological materials, and the determined results of As, Se, and Hg were consistent with the certified values.     

Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography use of an anion-exchange membrane to remove an ion-pair reagent from the eluent

Summary In order to enable the coupling of reversed-phase liquid chromatography (RPLC) with capillary gas chromatography (GC), the performance of an anion-exchange micromembrane device has been studied to remove the ion-pair reagent methanesulphonic acid from an acetonitrile/water LC eluent. The regenerant in the membrane was tetrabutylammonium hydroxide dissolved in acetonitrile/water, which effects an anion-exchange of methanesulphonate ions for regenerant hydroxide ions. The efficiency of the exchange process was found to be 99.9%. This enabled the direct introduction of the LC eluent, free of ions and with the proper acetonitrile/water ratio, into the GC. The applicability of the on-line LC-micromembrane-GC system has been illustrated for the potential drug eltoprazine, which is quantitatively recovered with a coefficient of variation for standard solutions of 3% at the 150 g/ml analyte level.     

Determination of arsenic, antimony, bismuth, selenium and tin in biological and environmental samples by continuous flow hydride generation ICP-AES without gas-liquid separator

Summary A simple continuous flow hydride generation system without conventional gas-liquid phase separator was developed for the determination of As, Se, Sb, Bi and Sn in biological and environmental samples by sequential ICP-AES with 1.5 kW power. The interchange of operating mode from normal solution nebulization to hydride generation or vice versa can easily be done without interrupting the plasma in this system.Two digestion methods were compared, i.e. the pressurized digestion with HNO₃ in a closed vessel and HNO₃/HClO₄/H₂SO₄ acid digestion in an open system. It was found that further treatment is necessary after normal pressurized digestion for As determination in marine samples, e.g. mussel. Interferences, especially by copper and nickel were examined and completely eliminated up to 10 g/ml by using a mixed reductant (3% NaBH₄ and 2% KI) with lower flow rate as well as the sample solution media of 30% HCl (v/v) and 20% HNO₃ (v/v). The effect of KI on the elemental oxidation states of As, Se and Sb is discussed. The accuracy of the method was validated by the analysis of a number of biological and environmental SRM's of NIST, BCR and NIES. Most results were in agreement with the certified values or reference values. The detection limits for these elements were in the range of 0.x ng/ml.On leave from Shanghai Institute of Metallurgy, Academia Sinica, Shanghai, China 200050     

Preconcentration Atomic Absorption Spectrophotometric Determination of Trace Lead(II) by Hydride Generation Combined with an Adsorbent Water Suspension Sampling Technique

The optimization of preconcentration atomic absorption spectrophotometric determination of trace lead(II) has been studied by using hydride generation and adsorbent water suspension sampling techniques. The uptake of lead(II) by a specially adapted chelate-forming resin, that is, a sulfonated dithizone (DzS)-loaded resin, was complete in the pH range 6.3-10. Lead adsorbed on DzS-loaded resin was successfully converted into its hydride in a medium, HCI --- H₂O₂ --- NaBH₄ without the need for a desorption procedure. Chelating agents except for DzS and DzS-loaded resin interfered seriously with the generation of lead hydride. Severe interference from diverse hydride-forming elements and transition metal ions is eliminated to a great extent by the treatment with DzS-loaded resin. The calibration curve obtained from the lead-bearing resin-water suspension was linear in the range of 5-500 ng/ml, whereas that from aqueous standard solution was in the range of 5-200 ng/ml. The detection limit of the method depends on the concentration factor and is 0.025 ng/ml in the present study. The proposed method was applied to the determination of trace lead(II) in environmental water samples.     

Determination of As(III) and total inorganic arsenic by on-line pretreatment in hydride generation atomic absorption spectrometry

Summary A method for the on-line prereduction of As(V) was developed in order to determine As(III) and As(V) with the same sensitivity by continuous flow hydride generation. In this procedure, the sample is continuously mixed with concentrated hydrochloric acid and a potassium iodideascorbic acid solution, flows through a heated PTFE-tube and is determined by hydride generation atomic absorption spectrometry in a heated quartz cell. The selective analysis of As(III) is carried out by continuous mixing of the sample with acetic acid and hydride generation. The method allows the rapid determination of inorganic arsenic species at concentrations down to 1 g/l. A manual sample preparation is not required.     

Determination of arsenic in fly ash by hydride generation in a slurry

We have studied the generation of arsenic hydride on a fly ash slurry from a thermal power plant burning lignite. The conditions for the formation of the slurry were optimized and the influence of the presence of various surfactants on the formation and stability of slurry (particle size-analytical signal ratio) were investigated.The As content in the ash was 78.7 g/g, with an rsd of 5.6% and a detection limit of 2.8 ng. The proposed method was successfully applied to the determination of arsenic in a certified ash sample (BCR-38). This method was applied to fly ash from a thermal power plant burning anthracite.     

Preconcentration and determination of inorganic arsenic using a multisyringe flow injection system and hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for inorganic arsenic determination at trace levels by hydride generation-atomic fluorescence spectrometry (HGAFS) is presented. Preconcentration on a solid-phase was carried out using a column packed with an anion-exchange resin (Amberlite IRA-410). The reagents are dispensed to the system using a multisyringe burette coupled with two multi-port selection valves.

Different parameters were changing in order to make the system as effective as possible. An analytical curve was obtained for arsenic determination between 50 and 2000 ng l⁻¹. This new approach improved five times the sensitivity over a MSFIA–HGAFS technique developed previously by the authors. Detection limit of the proposed technique was (3σ_b/S) of 30 ng l⁻¹. The relative standard deviation (R.S.D.) of As at 1 μg l⁻¹ was 4.8% (n=7). A sample throughput of 10 h⁻¹ has been achieved. The proposed method has been applied to different reference solid and water materials with satisfactory results.     

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.     

强碱阴离子交换树脂及碱性洗脱剂的离子排阻/阴离子交换色谱法同时测定NH4+ ，NO2-和NO3-（英文）

Ion-exclusion/anion-exchange chromatography(IEC/AEC) on a combination of a strongly basic anion-exchange resin in the OH——form with basic eluent has been developed.The separation mechanism is based on the ion-exclusion/penetration effect for cations and the anion-exchange effect for anions to anion-exchange resin phase.This system is useful for simultaneous separation and determination of ammonium ion(NH+4),nitrite ion(NO-2),and nitrate ion(NO-3) in water samples.The resolution of analyte ions can be manipulated by changing the concentration of base in eluent on a polystyrene-divinylbenzene based strongly basic anion-exchange resin column.In this study,several separation columns,which consisted of different particle sizes,different functional groups and different anion-exchange capacities,were compared.As the results,the separation column with the smaller anion-exchange capacity(TSKgel Super IC-Anion) showed well-resolved separation of cations and anions.In the optimization of the basic eluent,lithium hydroxide(LiOH) was used as the eluent and the optimal concentration was concluded to be 2 mmol/L,considering the resolution of analyte ions and the whole retention times.In the optimal conditions,the relative standard deviations of the peak areas and the retention times of NH+4,NO-2,and NO-3 ranged 1.28%-3.57% and 0.54%-1.55%,respectively.The limits of detection at signal-to-noise of 3 were 4.10 μmol/L for NH+4,1.87 μmol/L for NO-2 and 2.83 μmol/L for NO-3.     

Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina

A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid‐phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2‐mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type, and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng/L level and the limit of detection (3s) were found to be 2.3% and 12 ng/L, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.     

Determination of arsenic in ambient water at sub-part-per-trillion levels by hydride generation Pd coated platform collection and GFAAS detection

A method for trace determination of total arsenic in ambient waters is described. Arsenic is separated on-line from a large volume water sample by hydride generation and purging, pre-collected on a Pd coated pyrolytic platform cuvette using a simple and inexpensive system, and finally detected by GFAAS. Instrument parameters, hydride generation, transportation, and collection were optimized. The analytical behavior for major species including As(3+), As(5+), monomethyl As (MMA), and dimethyl As (DMA) were investigated individually. Problems arising from use of the system were discussed and eliminated. The necessity of sample digestion and an efficient digestion method were studied. Sample digestion for water with low organic content such as tap water and clean ground water and some clean surface water can be omitted. The method detection limit (MDL) is 0.3 ng l(-1) for a 25 ml water sample. Recoveries close to 100% with R.S.D.<5% can be easily achieved. Typical aqueous samples including tap, ground, lake, river, rain, sewage effluent, and saline water from different origins in the US, China, and Canada were collected and analyzed using ultra clean sampling and analysis techniques. The background levels of As in most water analyzed were established for the first time, and found to be far above the EPA's health effect criteria, 18 ng l(-1).     

Ion-exchange method for separation and concentration of platinum and palladium for analysis of environmental samples by inductively coupled plasma atomic emission spectrometry

An ion-exchange procedure is proposed for determination of Pt and Pd in environmental samples, using a Dowex 1-X10 anion-exchange resin. Pt and Pd were separated from the matrix elements in the sample by selective retention on the column as anionic chloro complexes and subsequent elution by circulated thiourea at 60 °C. The eluent, containing Pt and Pd was analyzed by inductively coupled plasma (ICP) atomic emission spectrometry (AES). Average recoveries of 98% and detection limit of 15 ng/g for both metals were achieved. Analysis of Pt and Pd concentrations in road dust, sampled from several sites in Germany was performed. The comparison of the obtained data with the concentrations of Pt and Pd in the same samples, determined by ICP-MS showed a very good agreement.     

Determination of arsenic in glass and raw materials for glass via quartz-tube hydride generation AAS after separation by solvent extraction

Summary A method is described for the determination of traces of arsenic in glass and raw materials for glass. After a digestion with hydrofluoric acid/sulphuric acid for glass and silica containing materials and varied digestion variants the arsenic is separated from the sample matrix by solvent-extraction of arsenic(III) chloride with toluene and back-extraction into water. The following determination is made by hydride generation atomic absorption spectrometry after atomisation in a heated quartz tube. A volatilization of arsenic during the digestion, different reagents for the oxidation and reduction of arsenic as well as the selectivity of the solvent extraction with regard to different interfering elements were investigated. It has been found that with the method developed, also at high concentrations of interfering elements, arsenic can be separated and a nearly interference-free determination of arsenic in glass and in raw materials for glass is possible. For example, at antimony concentrations of 60% (m/m) in the sample the detection limit is 0.5 g/g As₂O₃. The over-all detection limit is 0.05 g/g As₂O₃. The relative standard deviation is 5.7% (n=4) at a concentration of 3.6 g/g As₂O₃.