Simultaneous determination of arsenic,mercury, antimony and selenium in biological materials with prior collection of gaseous products followed by neutron activation analysis

A method combining prior collection of gaseous products with subsequent neutron activation analysis has been developed for simultaneous determination of traces of arsenic, mercury, antimony and selenium in biological materials. The generation of hydrides of arsenic, antimony and selenium and cold vapor of mercury in the vapor generaion and collection system was investigated by the use of radiotracers of the respective elements. The result indicates that selenium and mercury can be completely evaporated from the digested sample solution in 5M HCl with the addition of 5% sodium tetrahydroborate solution, while additional reduction proces by potassium iodide and ascorbic acid is needed for complete evaporation of arsenic and antimony. The gaseous products were collected in a quartz tube for neutron irradiation. The detection limits of these elements were fount to be in the range of 10^–7 to 10^–8 g under the present experimental conditions. The reliability was checked with NBS standard reference materials.     

Cold vapor atomic absorption spectrometric determination of mercury using sodium tetrahydroborate reduction and collection on gold

Summary Sodium tetrahydroborate(III) is equivalent to or better than tin(II) chloride as a reducing agent for mercury in cold vapor atomic absorption spectrometry using collection on gold. Concentrations of copper, silver, nickel, iodide, antimony, arsenic, bismuth and selenium typically found in water or waste water do not interfere. Prerequirements for satisfactory performance are that the gold is at a temperature below 100C during collection of mercury and that the gas from the reaction flask is washed with sodium hydroxide and dried with magnesium perchlorate. All determinations were carried out in 5 mol l^–1 hydrochloric acid and in the presence of 200 mg l^–1 iron(III). Detection limits (3) of 0.15 ng absolute, and of 15 ng l^–1 or 3 ng l^–1, using 10 ml or 50 ml solution, respectively, are obtained. The analytical curve is linear to 40 ng, and the relative standard deviation in the optimum working range is better than 2%.

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Kaltdampf-Atomabsorptionsspektrometrische Bestimmung von Quecksilber mit Reduktion durch Natrium-Tetrahydroborat und Sammeln auf Gold

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Dedicated to Prof Dr. W. Fresenius on the occasion of his 75th birthday     

The determination of arsenic and selenium in coal by continuous flow hydride-generation atomic absorption spectrometry and atomic fluorescence spectrometry

Concentrated perchloric acid is used to digest coal for subsequent determination of arsenic and selenium by hydride-generation atomic absorption and fluorescence spectrometry. Arsenic and selenium are removed from potentially interfering metal ions by coprecipitation with lanthanum hydroxide. The detection limits, 58 and 36 ng g^?1 by atomic absorption and 25 and 10 ng g^?1 by atomic fluorescence, for arsenic and selenium in coal, respectively, are adequate for the normal levels of these metals.     

Determination of organotin compounds in biological samples using accelerated solvent extraction,sodium tetraethylborate ethylation,and multicapillary gas chromatography–flame photometric detection

A method has been developed for species-selective analysis of organotin compounds in solid, biological samples. The procedure is based on accelerated solvent extraction (ASE) of analytes and includes extraction of the tin species with a methanol–water (90% methanol) solution of acetic acid/sodium acetate containing tropolone (0.03% w/v), their ethylation with NaBEt₄, and separation and detection by GC–FPD. The analytical procedure was optimized with an unspiked sample of harbor porpoise (Phocoena phocoena) liver. Effects of ASE operational variables (extraction temperature and pressure, solvent composition, number of static extraction steps) are discussed. Method detection limits (MDL) were in the range 6–10 ng(Sn) g^–1 dry weight and 7–17 ng(Sn) g^–1 dry weight for butyl- and phenyltin compounds, respectively. Recoveries were comparable with or better than those obtained by use of other procedures reported in the literature. The analytical procedure was validated by analysis of NIES No. 11 (fish tissue) certified reference material.     

Activation analysis of selenium in organic samples,through selenium-77m,on a pre-separation basis

A method is described to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with APDC at pH 1.5. The separation is made prior to the neutron irradiation and the correction for selenium in the reagents performed by the irradiation of a blank. The method has been successfully used in fodder samples as well as some other organic reference materials, using a fast pneumatic transfersystem, which takes the samples from the irradiation position to the counting position in 3s, with the only limitation of the thermal neutron flux available, 4.7·10¹¹ cm^–2·s^–1. Detection limits of 0.1 g are obtained under these experimental conditions.     

Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

Determination of tributyltin in sediments by hydride generation /GC/QFAAS

All steps involved in the determination of tributyltin in sediments by anhydrous acetic acid extraction, hydride generation, cold trapping, gas chromatographic separation and quartz furnace atomic absorption spectrometry are critically examined. Detection limits (1.8 ng Sn.g^–1) and reproducibility at representative concentration levels (6–12%) are satisfying for practical purposes.     

Determination of ochratoxin A in pig tissues by liquid–liquid extraction and clean-up and high-performance liquid chromatography

A fast, simple, and sensitive HPLC–FD method is described for determination of ochratoxin A (OTA) in pig kidney and muscle; a small mass (<2.5 g) of sample and a relatively small volume (<15 mL) of a non-halogenated extraction solvent are required. Ochratoxin B, systematically absent from all the samples investigated, was used as internal standard. Liquid–liquid partition was used for sample clean-up. Recoveries at the 1 ng g^–1 level were 86±15% and 74±8% for kidney and muscle, respectively, and detection limits were 0.14 and 0.15 ng g^–1. Clean-up by solid-phase extraction (SPE) is required for pig liver. A survey of the OTA content of tissues of pigs slaughtered in southern Italy revealed that 52 out of 54 analysed samples were contaminated; the OTA concentration in kidney ranged between 0.26 and 3.05 ng g^–1. The effect of measurement precision on compliance with legal limits is also discussed.     

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.     

Determination of selenium in foods by pseudo-cyclic neutron activation and anti-coincidence gamma-ray spectrometry

A pseudo-cyclic instrumental neutron activation analysis method in conjunction with anti-coincidence gamma-ray spectrometry (PC-INAA-AC) has been developed for the determination of ppb levels of Se. The method consists of repetitions of the irradiation-decay-counting cycles of a sample using the rapid transfer cyclic system at the Dalhousie University SLOWPOKE-2 reactor facility. The 162-keV γ-ray of ^77mSe (t _1/2 = 17.4 s) has been found to be highly selective. The precision and detection limits are significantly improved and the total experimental time drastically reduced by this method. Detection limits are between 2 and 9 ng. The accuracy of the method has been evaluated by analyzing a number of nutritional reference materials. The PC-INAA-AC method has been applied for the routine determination of Se to the composites of 135 food samples with values ranging from as low as 1 ng g⁻¹ for tea to 1,045 ng g⁻¹ for organ meats on fresh weight basis.     

Flow injection-hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth

A simple and robust flow injection system which permits low sample and reagent consumption is described for rapid and reliable hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth. The system, which composed of one peristaltic pump and one four channel solenoid valve, used water as the carrier streams for both sample and NaBH₄ solution. Rapid off-line pre-reduction of the analytes was achieved by using hydroxylamine hydrochloride for selenium and a mixture of potassium iodide and ascorbic acid for arsenic and bismuth. Transition metal interference was eliminated with the addition of thiourea and EDTA into the NaBH₄ solution and significant sensitivity enhancement was observed for selenium in the presence of thiourea in the reductant solution. Under optimised conditions, the method achieved detection limits of 0.2 ng mL⁻¹ for Se, 0.5 ng mL⁻¹ for As and 0.3 ng mL⁻¹ for Bi. The method was very reproducible, achieving relative standard deviations of 6.3% for Se, 3.6% for As and 4.7% for Bi, and has a sample throughput of 360 h⁻¹. Successful application of the method to the quantification of selenium, arsenic and bismuth in a certified reference river sediment sample is reported.     

Comparative study of atomic fluorescence spectroscopy and inductively coupled plasma mass spectrometry for mercury and arsenic multispeciation

Mercury and arsenic are two elements of undoubted importance owing to their toxic character. Although speciation of these elements has been developed separately, in this work for the first time the speciation of As and Hg using two atomic fluorescence detectors in a sequential ensemble is presented. A coupling based on the combination of high-performance liquid chromatography (where mercury and arsenic species are separated) and two atomic fluorescence detectors in series, with several online treatments, including photooxidation (UV) and hydride generation, has allowed the determination of mercury and arsenic compounds simultaneously. The detection limits for this device were 16, 3, 17, 12 and 8 ng mL^–1 for As^III, monomethylarsinic acid, As^V, Hg²⁺ and methylmercury, respectively. This coupling was compared with an analogous one based on inductively coupled plasma–mass spectrometry (ICP-MS) detection, with detection limits of 0.7, 0.5, 0.8, 0.9 and 1.1 ng mL^–1, respectively. Multispeciation based on ICP-MS exhibits better sensitivity than the coupling based on tandem atomic fluorescence, but this second device is a very robust system and exhibits obvious advantages related to the low cost of acquisition and maintenance, as well as easy handling, which makes it a suitable system for routine laboratories.     

Analysis of mercury(II), methylmercury and phenylmercury by RPHPLC with micellized dithizone post-column derivatization photometric detection

Post-column derivatization detection system based on dithizone solubilized in cetyltrimethyl-ammonium hydrogenesulfate micellar media at pH 2.0 was devised and evaluated for selective detection of mercury(II), methylmercury and phenylmercury in reversed-phase HPLC system with photometric detection at 500 nm. This reagent solution is fully compatible with acidic organo-aqueous mobile phases generally used in RPHPLC. With the aid of the detection systematic study of the retention behaviour of three mercury species on octadecylsilica sorbent was carried out. Influence of pH, acetonitrile volume fraction, complex forming additives was investigated in detail. In mobile phase consisting of 5–30% of acetonitrile in water at pH 2.0 and 2·10^–4 mol·I^–1 DCTA linear calibration curves were measured in range 20–1000 ppb with correlation coefficient better than 0.99. Detection limits were 1–5 ng for this three mercury species. Interferences of copper(II) and silver(I) are negligible.     

A direct solid sampling electrothermal atomic absorption spectrometric method for determination of trace elements in zirconium dioxide

A direct solid sampling electrothermal atomic absorption spectrometric method for determination of Cd, Co, Cr, Cu, Fe, Li, Mn, Ni and Zn in zirconium dioxide has been developed. Using optimised experimental conditions, very effective in-situ analyte/matrix separation was achieved without any chemical modification. After the measurement, the matrix residue could easily be tipped out from the platform. In the determination of Cr, before sampling, the platform bottom was covered with carbon powder. Quantification was performed using calibration curves measured with aqueous standard solutions pipetted onto the matrix residue from a previous sample run. Sample amounts between 0.5 and 40 mg were applied for each analysis cycle. The accuracy was determined by comparison of the results with those obtained by radiochemical neutron activation analysis and by electrothermal atomic absorption spectrometry using liquid sampling of digests and slurry sampling. For the nine elements assayed, the limits of detection achievable by this method are between 0.06 ng g^–1 (Cd) and 2.3 ng g^–1 (Fe).Dedicated to the memory of Wilhelm Fresenius     

Ultratrace characterization of AlSiCu sputter targets for Th,U and 35 other elements by neutron activation analysis

Instrumental and radiochemical neutron activation analysis has been applied to a comprehensive trace characterization of AlSiCu sputter targets. By instrumental neutron activation analysis via long-lived indicator radionuclides, up to 33 elements were assayed with detection limits between 0.01 and 200 ng·g^–1. The high activity of⁶⁴Cu and²⁴Na produced from the matrix significantly limits the instrumental performance via short- and medium-lived indicator dionuclides. For this reason, a radiochemical separation was developed based on adsorption of²⁴Na on hydrated antimony pentoxide and extraction of⁶⁴Cu by diethylammonium diethyldithiocarbamate from HCl medium. By this radiochemical method, As, Ga, K, La, Mn, Mo, Re, Sb, U and W could be assayed via medium-lived radionuclides and the achievable limits of detection were between 0.1 and 25 ng·g^–1. Further improvement of detection limits for U and Th was achieved by a selective radiochemical separation of²³⁹Np and²³³Pa on a Dowex 1×8 column in HF and HF/NH₄F medium providing limits of detection for U and Th of 0.06 and 0.02 ng·g^–1, respectively. These techniques were applied to the analysis of two AlSiCu sputter target materials. Results are compared with those of glow discharge mass spectrometry.     

Trace element determination in high-purity scandium by neutron activation analysis and pre-irradiation matrix separation

A pre-irradiation separation procedure has been developed for the determination of trace elements in high-purity scandium by neutron activation analysis. The sample is dissolved in high-purity concentrated hydrochloric acid and scandium is extracted with the same volume of a solution of 50 vol.% bis(2-ethyl hexyl)-orthophosphoric acid (HDEHP) in toluene. The scandium matrix is removed from the most important trace impurities and the residual amount of Sc is in the range of 0.001%. The separation is carried out in the vial to be used in irradiation to prevent sample contamination. Detection limits in the ppb range were achieved with a sample of 10 mg, a thermal neutron flux of 2 · 10¹³ n · cm^–2 · s^–1 and an irradiation time of 48 hours. Most of the elements sought in two samples of high-purity scandium were below the detection limits.     

Nanogram determination of arsenic in biological reference materials by non-destructive Compton suppression neutron activation analysis

Summary Non-destructive epithermal neutron activation analysis in conjunction with Compton suppression has been applied to determine arsenic in seven biological standard reference materials from the National Institute of Standards and Technology. The accuracy is in excellent agreement with all the certified values and compilation results. For four of the materials detection limits between 1–4 ng/g were easily achieved while for three others they ranged from 18–50 ng/g. Overall analytical precision typically varied between 2–4% for five of the reference materials while for two other it was between 12–16%. These methods clearly demonstrate that through a judicious approach of anti-coincidence techniques, nanogram quantities of arsenic can be reliably determined without the need for labor intensive chemical separations.     

Microcolumn preconcentration and gas chromatography-microwave induced plasma-atomic emission spectrometry (GC-MIP-AES) for mercury speciation in waters

A novel method for the direct determination of mercury species at the ng l^–1 level in natural waters is described. Methyl-, ethyl- and inorganic mercury are preconcentrated on a sulphhydryl cotton microcolumn incorporated in a flow injection system. Retained mercury species are then eluted with hydrochloric acid solution (3 mol/l) and subjected to phenylation before determination by gas chromatography-microwave induced plasma-atomic emission spectrometry. Limits of detection for mercury species are 10 ng l^–1 for methyl- and ethyl-mercury and 16 ng l^–1 for inorganic mercury based on processing 200 ml of sample. Application of the methodology to waters of the Manchester Ship Canal revealed elevated levels of methylmercury and inorganic mercury.     

Evaluation of various sample pre-treatment methods for total and inorganic mercury determination in biological certified reference materials by CVAAS technique

Sample preparation methods for non-separation cold vapor atomic absorption spectrometry (CVAAS) sequential inorganic mercury speciation in biological certified reference materials (CRMs) were investigated. The methylmercury concentration was calculated as the difference between total and inorganic mercury. Microwave-assisted decomposition method, and three ultrasonic extraction procedures based on acid leaching with HCl and HCOOH and solubilization with TMAH were employed as sample preparation methods. The replacement of a sample decomposition procedure by extraction prior to analysis by CVAAS, as well as the aspect of speciation analysis is discussed. The limits of detection in the sample were determined as 50 and 10 ng L⁻¹ for inorganic and total mercury, which corresponds to absolute detection limits of 40 and 8 ng g⁻¹ for inorganic and total mercury, respectively. The results were in good agreement with the 95% confidence level t-test of the certified values for total and inorganic mercury in the reference materials investigated. From the analysis of the CRMs, it was evident that the difference between the total and inorganic mercury concentrations agrees with the methylmercury concentration. The relative standard deviation was better than 11% for most of the samples.      

Sequential hydride generation/pneumatic nebulisation inductively coupled plasma mass spectrometry for the fractionation of arsenic and selenium species

The toxicity of certain elements is known to be related to their organic substituents and/or oxidation states. As such, total elemental determinations do not always yield sufficient information for accurate risk assessments and therefore speciation or fractionation data are required. In order to obtain fractionation data for trace levels of arsenic and selenium, a novel sequential pneumatic nebulisation (PN)/hydride generation (HG) inductively coupled plasma mass spectrometry (ICP-MS) method was developed. The method offers the advantage of sample introduction via either PN or HG by simply rotating a 4-way switching valve while the system is in operation. In PN mode, the liquid sample is aspirated into ICP, allowing for the determination of the total amount of each element, whilst in HG mode only the arsenic and selenium species that form volatile hydrides are determined. Conveniently, in the case of arsenic, this allows for differentiation between the four most toxic arsenic species (arsenate, arsenite, monomethylarsonic acid and dimethylarsinic acid), which form volatile hydrides, and the virtually non-toxic forms (arsenobetaine, arsenosugars, etc.), which do not. This allows for the rapid estimation of the amounts of toxic and non-toxic arsenic species present in a sample. For arsenic, the technique gave detection limits of 36 ng l⁻¹ in PN mode and 1 ng l⁻¹ in HG mode. For selenium, detection limits of 150 ng l⁻¹ were achieved in PN mode and 220 ng l⁻¹ in HG mode. The technique also gave good long- and short-term stabilities of under 6% RSD for both elements. A variety of samples, including water and urine standard reference materials, were analysed in both modes, and the precision and accuracy of the results for total arsenic and selenium levels were assessed. Using the technique in both modes also allowed for the fractionation of As and Se species into their volatile hydride-forming and non-hydride-forming species. This was particularly informative, with respect to As species present, in the case of a kelp powder extract. Digested tobacco samples were only analysed for their total As levels, in which case results obtained via both sample introduction modes showed good agreement.