Determination Of Total Arsenic Research Articles

A FIA-system for As(III)/As(V)-determination with electrochemical hydride generation and AAS-detection.

A flow-injection system with electrochemical hydride generation and atomic absorption detection for As(III)/As(V) determination is described. A simple electrolytic flow-through cell has been developed and optimized. Several cathode materials like Pt, Ag, Cu, C and Pb have been tested. The influence of the electrolysis current, concentration of sulfuric acid, carrier stream, flow rate, sample volume and interferences by other metals on the arsenichydride generation have been studied. For the determination of total inorganic arsenic, As(V) is reduced to As(III) on-line by postassium iodide or L-cysteine at 95 degrees C. The influence of the temperature and the reduction medium on this pre-reduction step has been tested. The calibration curve is linear in the range of 5 to 50 microg/L for As(III) and total inorganic arsenic and shows a higher sensitivity than in case of reduction with sodium tetrahydroborate. The detection limit is 0.4 microg/L for As(III) and 0.5 microg/L for total inorganic arsenic at a sample volume of 1 mL.

Preliminary studies on arsenic species in some environmental samples.

Arsenic compounds have been determined in some environmental samples from the German Environmental Specimen Bank (ESB) (marine mussels, freshwater mussel and fish, sea-gull eggs) and certified reference materials (DORM-1, DOLT-1, NBS Oyster Tissue) after separation by open column cation and anion exchange chromatography by two different methods of total arsenic determination in separated fractions (instrumental neutron activation analysis or hydride generation atomic absorption spectrometry). Arsenobetaine has been identified as the major species in all the different materials.

Determination of total arsenic in soils by differential-pulse cathodic stripping voltammetry

A procedure which permits the determination of total arsenic in soils using differential-pulse cathodic stripping voltammetry at a hanging mercury drop in the presence of copper after the acid digestion of solid samples in a closed-vessel microwave digester was developed. Optimized conditions include accumulation potential –0.5 V, accumulation time 120 s, 0.05 mol l–1 of KI to reduce AsV to AsIII, 10 µg ml–1 of copper and both 3.8 mol l–1 HCl and 0.24 mol l–1 NaHCO3 as electrolyte. The detection limit was 50 pg ml–1 and the reproducibility was 3.8% intra-day and 4.5% inter-day for 10 determinations at a concentration of 2.6 ng ml–1. The method was applied to a reference certified soil sample, obtaining a relative error of 0.7%. Results for 12 soil samples from a zone of the Basque Country were compared with those obtained by hydride generation atomic absorption spectrometry.

Determination of total arsenic in serum and packed cellsof patients with renal insufficiency.

In order to investigate the arsenic level in serum and packed cells of patients with renal insufficiency, total arsenic (As) concentrations were determined with hydride generation atomic absorption spectrometry (HGAAS) in serum (S) and packed cells (PC) of 31 non-dialyzed patients. The accuracy of the method was tested by the analysis of arsenic in 3 certified reference materials. Patients showed a three-fold increase of arsenic concentrations in serum and a two-fold increase of arsenic in packed cells compared with controls. Patients (n=10) with higher serum creatinine (>2.0 mg/dL), urea (>0.70 g/L) and urinary protein (mean+/-SD: 1.12+/-0.82 g/L) showed higher arsenic concentrations (5.8+/-3.3 microg/L in serum and 18.0+/-16.7 microg/kg in packed cells) compared with those with lower creatinine (<1.6 mg/dL), urea (<0.6 g/L) and urinary protein (mean+/-SD: 0.27+/-0.82 g/L) (n=16, serum arsenic 1.2+/-1.2 microg/L, packed cells arsenic 2.6+/-1.9 microg/kg). The significant differences (both p < 0.001) in S and PC-arsenic levels of patients in group I and II implies a relationship between the arsenic level and the degree of chronic renal insufficiency.

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).

Speciation of arsenic by the determination of total arsenic and arsenic(III) in marine sediment samples by electrothermal atomic absorption spectrometry

A method for the determination of arsenic(III) and total arsenic was studied. Arsenic(III) was chelated with 2% sodium diethyldithiocarbamate in water, extracted with isobutyl methyl ketone and determined by electrothermal atomic absorption spectrometry, using palladium as chemical modifier. The effects of pH, extraction time and amounts of reagents required for the extraction were studied. The detection limit of this method was 25 µg kg–1. Different modifiers [LaCl3–HNO3, Pd–Mg(NO3)2] for the total arsenic determination in slurries of marine sediment samples were also investigated; LaCl3–HNO3 was avoided because a double peak was observed. The detection limit for the determination of total arsenic using Pd–Mg(NO3)2 as modifier was 44 µg kg–1. The precisions obtained for the different amounts of arsenic(III) and total arsenic were 0.57–2.99 and 0.83–0.45%, respectively. The graphite furnace programmes, accuracy and interferences for both procedures were also studied. The method has been applied to the determination of arsenic(III) and total arsenic in sediment samples from Galicia (North West of Spain).

Determination of total arsenic in serum and packed cells of patients with renal insufficiency

Determination of total arsenic in serum and packed cells of patients with renal insufficiency

Differential-pulse voltammetric determination of total arsenic following its volatilization as AsH3and absorption in silver nitrate solution

A procedure is described for the volatilization of inorganic arsenic(III) and arsenic(V) as AsH3 and the absorption of AsH3 in a silver nitrate solution. For the absorption of AsH3, a specially designed glass cell has been used which cycles the absorption solution, utilizing the principle of a mammouth pump. In the adsorption solution, arsenic(III) is determined by differential-pulse voltammetry. The procedure is applicable in the concentration range from 1 × 10–6 to 5 × 10–5 mol l–1.

Arsenic determination in environmental, biological and food samples by inductively coupled plasma mass spectrometry

Methodology developed with inductively coupled plasma mass spectrometry (ICP-MS) for the determination of total arsenic in soil, house dust, and children's daily diet and faecal samples is described. Microwave oven dissolution, high temperature, pressure vapour phase acid digestion, and dry ashing with conventional thermal and microwave furnace heating and Mg(NO3)2 ashing aid are compared for sample preparation. Arsenic recovery from reference materials and spiked samples is between 94.8 and 109%. The ICP-MS Elan 5000a As detection limits (3sb) were 2.0 ng g–1 in freeze-dried human faeces prepared by closed-vessel, microwave-heated digestion and 1.1 ng g–1 in freeze-dried children's diets prepared by furnace ashing with an ashing aid.

Determination of arsenic in sea water by cathodic stripping voltammetry in the presence of pyrrolidine dithiocarbamate

A procedure is presented for the determination of arsenite and total arsenic in sea water using differential pulse cathodic stripping voltammetry at a hanging mercury drop electrode in the presence of pyrrolidine dithiocarbamate (PDC). The deposition potential was −0.3 V, whereas the scan was initiated from 0 V. Optimised conditions include a PDC concentration of 0.5 μM and a pH ≈ 0.8. The detection limit of the method is 3 nM As. The method was tested by analysis of CASS-2 certified sea water and applied to determination of arsenic in Atlantic ocean water.

Determination of total and leachable arsenic and selenium in soils by continuous hydride generation inductively coupled plasma mass spectrometry

A novel gas–liquid separator has been designed for continuous hydride generation inductively coupled plasma mass spectrometry, incorporating a water trap to remove solution droplets from the gas stream. The system has been applied to the determination of total and leachable arsenic and selenium in soils of the Western Cape region of South Africa. Samples were prepared by alkaline fusion for the determination of total concentrations, and leaching with 1 mol l–1 ammonium nitrate was used to determine the leachable content. Use of the hydride generation system confers a 40-fold increase in sensitivity over conventional nebulization, and eliminates argon chloride interferences. Detection limits were in the range 0.2–1.0 µg l–1. Certified reference materials were analysed, and good agreement was obtained.

Efficient procedures for the voltammetric determination of total arsenic in zinc and cadmium plant electrolyte process streams and in industrial effluents

Voltammetric methods for determining total arsenic in zinc and cadmium electrolyte process solutions and in treated effluent samples are described. The method for plant electrolyte couples reductillation with cathodic stripping voltammetry at a hanging mercury drop electrode. Reductillation, a process in which AsV is reduced to AsIII and AsIII is subsequently distilled into a separate compartment, overcomes interference from high levels of copper and cadmium in neutral leach clarifier overflow and in cadmium leach filtrate and reduces the electroinactive AsV to the electroactive AsIII species. This method is suitable for the determination of arsenic concentrations down to 0.07 mg l–1 and can be used in either off- or on-line modes. In treated effluent, the arsenic concentration is in the low µg l–1 range, and the reductillation technique lacks the required sensitivity. However, the concentration of interfering ions is also low and a direct determination of the total arsenic concentration by cathodic stripping voltammetry is possible after reduction of the AsV species. Cysteine was found to be a better reducing agent than sulfite. However, to achieve online arsenic determination, which was an important requirement of the study, sulfite was the preferred reducing agent because of its long-term stability in solution.

Analysis and Removal of Arsenic From Natural Gas Using Potassium Peroxydisulfate and Polysulfide Absorbents

Abstract Natural gas from the large Abo gas field in southeastern New Mexico contains arsenic (0.2 to 2.5 μg/L) in the form of trialkylarsines. A method of analysis for arsenic which is based on the extraction of the alkylarsines into a saturated solution of potassium peroxydisulfate (PPDS) followed by determination of total arsenic, as AsO4 −3, by hydride generation- d.-c. helium plasma emission spectrometry (HG-DCHPES) is described. The extraction of the alkylarsines was carried out by either shaking 1L gas samples with PPDS or sparging the gas in PPDS solutions. Analytical results of acceptable precision can be obtained using either procedure. Temperature (24°—45°C) or pH (1.10-4.10) had little effect on the As concentrations obtained by the sparging method. The measured arsenic concentrations of natural gas samples stored in Cr-Mo steel cylinders decrease with time of storage (-30% in the first 4 weeks). A standard blend of trimethylarsine in CH4 (1 mole TMA in 106 moles of CH4), stored in nickel-containing steel cylinder, showed a similar decrease in As concentration with time. The measured arsenic concentrations increase when the temperature of a cylinder of natural gas is heated indicating that part of the alkylarsines may be present in a condensed or physically adsorbed form on the inner walls of the cylinder. Scanning electron microscopy with X-ray microanalysis of the metal powders (Ni, Cr, Mo, Fe) contacted with TMA indicate that arsenic-rich solids also containing C and O are formed in the case of Ni and Cr. This phenomenon may represent an additional factor in the observed decrease in As concentration with time of storage. Polysulfides in solution form (Na2Sx) or solid (Na2S4) can quantitatively remove the trialkylarsines from natural gas.

Determination of total arsenic and speciation of arseno-betaine in marine fish by means of reaction ? headspace gas chromatography utilizing flame-ionization detection and element specific spectrometric detection

Marine organisms contain amounts of arsenic ranging from less than 1 μg/g to more than 10 μg/g. In food examinations usually total arsenic is determined, rarely As(III) and As(V) additionally. Rating marine food according to its total arsenic contents without further speciation, would involve an overcritical assessment. Due to the lack of suitable methods for routine analysis in food-control, the “organic” moiety remains unspecified. Only after performing a systematic research onto the real existence of arsenic and its compounds relevant to marine organisms, a toxicological evaluation can be carried out. As to its quantitative occurrence and its negligible toxic relevance arsenobetaine is of decisive importance. Therefore a reliable method has been developed based on headspace gas chromatography after chemical reaction. The predominant role of arsenobetaine in the organic arsenic moiety as well as in total arsenic in marine fish could thus be demonstrated.

Effect of cysteine on the speciation of arsenic by using hydride generation atomic absorption spectrometry

The use of hydride generation techniques for arsenic species is pH dependent. Identical responses can not be obtained from arsenite, arsenate, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) when the same acid concentration is used. Thus some methods commonly used for the direct determination of total arsenic under compromised conditions are subject to error. This error is eliminated by the addition of 2% cysteine to samples prior to hydride generation. In the presence of cysteine the optimum condition for the determination of these arsenic species is in the same range, and a single arsenic species can be used for calibration. This finding is applied to the determination of arsenic in human urine by using flow injection, hydride generation, and atomic absorption spectrometry methodology. The effect of cysteine and thioglycerol is reported in detail, and it is proposed that arsenate. MMAA and DMAA all in the As(V) state, are reduced to the As(III) state as organo-sulfur-arsenic(III) compounds through the reaction between the arsenic species and the thiol. These products, organosulfur derivatives of arsenic(III), easily react with tetrahydroborate(III) under similar conditions to afford the arsines without interference from cysteine. Non-thiol-containing amino acids such as methionine, glycine and histidine do not react with arsenic species in this way, and therefore they do not affect the pH dependence of the generation of arsenic hydride species.

Determination of total arsenic in environmental samples from Kumasi and Obuasi, Ghana.

The total arsenic content of some Ghana food and cash crops from Kumasi and Obuasi farms and markets was determined. Quantitative analysis of arsenic was also conducted on vegetation, cooked food obtained from some homes, local fish, and meat, as well as some soil and water samples. In all, 266 samples were examined. Values for Kumasi samples ranged from 0.07 to 7.20 mg/kg arsenic, whereas those for Obuasi ranged from 0.12 to 70.50 mg/kg, confirming that arsenic levels for Obuasi are much higher than those for Kumasi.

Electrochemical methods for the determination of total arsenic and arsenic compounds

AbstractThe determination of total arsenic and of arsenic compounds in biological and inorganic samples is a task frequently encountered by analysts. Several elecrochemical methods have been developed for the determination of total arsenic (generally after mineralization of the sample), arsenite, arsenate, methylarsonic acid and dimethylarsinic acid. The electrochemical behavior of several other organic arsenic compounds was also studied. This paper reviews these electrochemical methods, their application to environmental samples, and the problems encountered in the electrochemical determination of arsenic and arsenic compounds.

Generation of AsH 3 from As(V) in the absence of KI as prereducing agent: Speciation of inorganic arsenic

It is shown that the potassium iodide to the samples to reduce As(V) to AS(III) is not essential when total inorganic arsenic is determined by molecular spectrophotometry (trapping AsH 3 in Ag—DDTC) or by atomic-absorption spectrometry (if Ar flow-rate and NaBH 4 addition rate are controlled in 6 M hydrochloric acid medium). Furthermore, in the presence of low concentration of organic arsenic, a method is reported for the selective determination of inorganic As(III) and As(V), based on the use of citrate/citric acid medium to determine As(III) and hydrochloric acid to determine total inorganic As. As(V) is determined by the difference between total inorganic As and As(III). The interference level of organic arsenic species (monomethylarsenic acid and dimethylarsenic acid) in the determination of total inorganic arsenic and AS(III) in 6 M hydrochloric acid and citrate/citric acid medium respectively, is reported in the text. The developed method is applied to determine As(III) and As(V) in spiked, tap and waste waters and in lake sediments.

On-line preconcentration of arsenic from water samples with an anion-exchanger column coupled to a hydride generation ICP system

An on-line anion-exchange preconcentration hydride generation ICP system for the determination of total inorganic arsenic in water is described. The column was packed with strongly basic anion-exchange resin (AG 1-X8). Experimental conditions including pH of the sample solution, eluent, flow rate of eluent, oxidation states of arsenic and competing anion ions were studied. Compared with the conventional continuous hydride generation ICP, a 9.2-fold improvement in sensitivity was obtained with RSD 1–2% at 100 ng/ml. The detection limit (3σ) was 0.08 ng/ml. The recoveries in water samples were satisfactory. The system provides complete automation of sample loading, eluting and regenerating of the resin.

Observations on the use of a sulfuric acid medium for As(V) to As(III) reduction in lodimetric titrations: Application to the determination of total arsenic

The use of a sulfuric rather than a hydrochloric acid medium for the reduction of As(V) to As(III) by iodide is proposed. Optimum conditions of acid concentration, amount of sodium hydroxide, and time and temperature are established to achieve quantitative reduction. The optimized reduction procedure was applied to the iodimetric determination of total arsenic and compared to a procedure that employs a hydrochloric acid medium. A systematic error of 0.04% was found for the method with a sulfuric acid medium opposed to 0.05% for the method with a hydrochloric acid medium in the reduction step. The proposed modified iodimetric method has been successfully used with some organic samples requiring a prior destructive treatment of the organic matrix.