Routine determination of mercury,arsenic and selenium by radiochemical Neutron Activation Analysis

A method for the determination of mercury, arsenic and selenium by neutron activation analysis is described. Radiochemical separations are performed by selective distillation followed by electrolysis of mercury on gold and precipitation of arsenic and/or selenium by reduction to the elemental form. The chemical yields are 80–90% for mercury and 90–100% for arsenic and selenium. Interference tests have been carried out with reference to those elements most likely to interfere with the analysis. Detection limits for mercury, arsenic and selenium using 0.1 g of sample are 0.2 ng g^–1, 2 ng g^–1 and 3 ng g^–1, resp. Detection limits can be improved using greater sample size and neutron flux density. Results from the analysis of several NBS standard reference materials are given.     

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.     

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.     

Extraction procedures for chemical speciation of arsenic in atmospheric total suspended particles

An arsenic chemical speciation study was performed in 2000, using air filters on which total suspended particles (TSP) were collected, from the city of Huelva, a medium size city with huge industrial influence in SW Spain. Different procedures for extraction of the arsenic species were performed using water, NH₂OH.HCl, and H₃PO₄ solutions, with either microwave or ultrasonic radiation. The best optimised extraction methods were use of 100 mmol L^–1 NH₂OH.HCl and 10 mmol L^–1 H₃PO₄ and microwave radiation for 4 min. High-performance liquid chromatography coupled with hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) was employed for determination of the arsenic species. The results from 12 TSP air filters collected on a monthly basis showed extraction was quantitative (94% with NH₂OH.HCl and 86% H₃PO₄). Only inorganic arsenic species (arsenite and arsenate) were detected. The mean arsenite concentration was 1.2±0.3 ng m^–3 (minimum 0.3 ng m^–3, maximum 1.8 ng m^–3). The mean arsenate concentration was 10.4±1.8 ng m^–3, with greater monthly variations than arsenite (minimum 2.1 ng m^–3, maximum 30.6 ng m^–3). The high level of arsenic species in the TSP samples can be related to a copper smelter located in the region.     

Gas chromatographic determination of arsenic in low concentrations in inorganic materials

Summary A method is described for the quantitative chlorination and extraction of arsenic as arsenic trichloride from a number of alloys. The conditions for the quantitative gas chromatographic measurement of the volatile chloride have been studied. The proposed method for inorganic materials is very fast giving results within 10 min; sensitive, 1.5·10^–13 g As can be detected, simple and accurate. At the ng level of As the error is about 20% with a standard deviation less than 20%, and at the 10pg level the error is about 36% with a standard deviation of 44%.     

Simultaneous determination of arsenic and selenium in biological samples by HG-AFS

A new method is proposed for simultaneous determination of traces of arsenic (As) and selenium (Se) in biological samples by hydride-generation double-channel non-dispersive atomic-fluorescence spectrometry (HG-AFS) from tartaric acid media. The effects of analytical conditions on fluorescence signal intensity were investigated and optimized. Interferences from coexisting ions were evaluated. Under optimum conditions linear response ranges above 20 g L^–1 for As and 32 g L^–1 for Se were obtained with detection limits of 0.13 and 0.12 g L^–1, respectively. The precision for elevenfold determination of As at the 4 g L^–1 level and of Se at the 8 g L^–1 level were 2.7 and 1.9% (RSD), respectively. Recoveries of 92.5–95.5% for As and 101.2–108.4% for Se were obtained for four biological samples and two certified biological reference materials. The proposed method has the advantages of simple operation, high sensitivity, and high efficiency; it was successfully used for simultaneous determination of As and Se in biological samples.     

Application of standard materials and standard reference materials in the analysis of lead in blood

Summary Valuable information can be obtained at little expenses from quality control samples prepared in-house to monitor the determination of blood lead by atomic absorption spectrophotometry. Commercially manufactured control materials can also be used for this purpose. These materials are compared to standard reference materials which at present are available.The relative standard deviations for analysis of NBS standard reference materials were 15.4–2.8% (range 60–754 g/l) and in agreement with the relative standard deviation estimated for the analytical method. The corresponding figures for BCR control reference materials were lower: 1.1–1.4% (range 134–795 g/l).The average analytical bias demonstrated by analysis of NBS standard reference material and BCR control reference material were 3–6% (range 795–60 g/l) and in agreement with bias estimated by analysis of commercially manufactured and in-house prepared control materials.     

Thallium determination in reference materials by Isotope Dilution Mass Spectrometry (IDMS) using thermal ionization

Summary Using Isotope Dilution Mass Spectrometry (IDMS) with thermal ionization, thallium concentrations were determined in reference materials from NIST and BCR, from other sources, and reference materials from the German Environmental Specimen Bank. ²⁰³Tl spike solution is applied for the isotope dilution technique. Thallium concentrations in the investigated materials range from 2.67 g Tl·kg^–1 to 963 g Tl·kg^–1 with a relative standard deviation from 0.14 to 10%. The detection limit was 0.1 ng thallium for this work.     

Neutron activation analysis of semiconductor materials

Two examples of the use of neutron activation analysis for the characterization of semiconductor materials are given. 23 elements were determined in ASTM silicon intercomparison samples. Most elements are below the detection limits, which vary between 0.009–300 ng/g. CdS/CdTe thin films have been characterized by determining the Cd, Te, Cl, I and In concentrations of dissolved films. Parallel determinations in different samples of films prepared under identical conditions agreed within 0–53% (average deviation 21%) for Cl, Cd, In and I in CdS and 1.6–22% (average 8.7%) for Cd and Te in CdS/CdTe, respectively. It was determined both by NAA and resonance ionization spectrometry (RIS). The order of magnitude of the results was 1 ng/g and they agree within the range 7–64% (average difference 25%). The analytical procedures are described and discussed.     

Radiochemical studies on the extraction of arsenic(III) by trilaurylamine oxide and benzene from aqueous iodide solutions and its determination in water samples by spectrophotometry

An extraction system consisting of trilaurylamine N-oxide and benzene has been identified as a possible extractant for tracer arsenic (<10^–3 M) from hydrochloric or sulfuric acid solutions with or without iodide. Benzene alone is less efficient as an extractant for arsenic when compared with trilaurylamine oxide dissolved in benzene. The mechanism of extraction is attributed to the formation of hydrated AsCl₃, while the iodide complex is most probably AsI ₄ ^– . The role of the solvent and the other parameters affecting the extraction have been investigated. The results have been employed to determine arsenic in water samples by spectrophotometry using the molybdenum blue method. The extraction procedure was used for the analysis of 10 ml water samples containing 0.2–0.5 g of arsenic.     

Determination of arsenic by arsine generation with reducing tube followed by graphite furnace atomic absorption spectrometry

Summary A sensitive method for hydride generation and graphite tube furnace atomic absorption spectrometric measurements with a reducing tube has been developed for the determination of arsenic in tea and orchard leaves. Arsines were generated in a horizontal glass tube, in which a pellet of NaBH₄ was placed. 1.5–2.0 l/min of argon flow rate and 2,400° C of atomization temperature were the best experimental conditions. The strong supression of the arsenic signal by Ni and Co was effectively eliminated with 1,10-phenanthroline. A detection limit of 0.3 ng was obtained with a precision of 3–4%.Paper read at the Meeting of the Japan Society for Analytical Chemistry, June 1980     

Determination of toxic and non-toxic arsenic species in urine by microwave assisted mineralization and hydride generation atomic absorption spectrometry

Flow injection — microwave oven — hydride generation — atomic absorption spectroscopy (FI-MO-HG-AAS) has been optimized for the determination of the total and toxic arsenic in urine with and without persulfate, respectively. With microwave oven assisted digestion of urine with 5% (w/v) K₂S₂O₈ and 5% (w/v) NaOH all arsenicals completely can be converted to arsenate, which is determined by HG-AAS to give the total concentration of the six species present in urine. The detection limits of 4–6 g l^–1, the relative standard deviation of 3–7% and the high sample throughput make the methods suitable for rapid routine on-line determination. Application of the proposed procedures to the analysis of urine from people on a diet rich in seafood revealed a significant increase in total urinary arsenic due to the rapid excretion of organoarsenicals. Efficient decomposition and quantitative recovery of all arsenic species in spiked urine is achieved by using 5% K₂S₂O₈ in 5% NaOH at 4.6 ml min^–1, microwave power of 700 W and a 1.5 m coil.     

Slurry procedures for the determination of cadmium and lead in cereal-based products using electrothermal atomic absorption spectrometry

Simple and rapid methods for the determination of cadmium and lead in biscuits, bread and cereal-based products using the slurry-ETAAS approach are discussed. Suspensions were prepared in a 20% v/v ethanol medium. Phosphate was used as a chemical modifier for lead determination. For cadmium determination both palladium and a copper plus ammonia mixture were used. In both cases platform atomization was used and calibration was performed using aqueous standards. Results for two reference materials confirmed the reliability of the procedures. Relative standard deviations were in the range of 2.5–6.5% for cadmium and 4.5–14% for lead. Detection limits were, respectively, 0.5 and 8 ng/g.     

Determination of arsenic species in marine organisms by HPLC-ICP-OES and HPLC-HG-QFAAS

Separation and quantification of six arsenic species have been performed in cod, tuna and mussel samples by high performance liquid chromatography (HPLC) using inductively coupled plasma-optical emission spectrometry (ICP-OES) and hydride generation-quartz furnace atomic absorption spectrometry (HG-QFAAS) as detection techniques. It has been shown that arsenic extraction with a water-methanol (11) mixture is sufficiently quantitative for the cod and tuna, in which arsenic is mainly present as arsenobetaine (about 90% of total As extracted). In contrast, only 60% of the element is extracted from the mussels and the chromatograms obtained reveal the presence of an unknown compound. Detection limits are in the g ml^–1 range for the HPLC-ICP-OES technique (quantification of arsenobetaine and arsenocholine) and in the ng ml^–1 range for the HPLC-HG-QFAAS system (quantification of arsenite, arsenate, monomethylarsonic and dimethylarsinic acids).     

Determination of pefloxacin in serum and pharmaceutical forms by derivative spectrophotometry

A method for the direct determination of pefloxacin in serum and pharmaceutical forms (tablets and ampoules) has been developed, based on the use of second-order derivative ultraviolet spectra. Spectrophotometric assay of pefloxacin in tablets and ampoules was carried out in 0.1 mol/L NaOH, while in serum it was performed in 0.1 mol/L NaOH with the addition of sodium dodecylsulfate, in 337–347 nm wavelength range. Linear calibration curves were obtained in the concentration ranges 2–30g/mL pefloxacin for tablets and ampoules and 0.12–5 g/ mL for serum samples. Relative error of determination, as criterion for accuracy, was less than 1%, while the precision was better than 4 ng/ml. The minimum detectable concentration of pefloxacin in serum was 15 ng/mL.     

Speciation of dimethylarsinyl-riboside derivatives (arsenosugars) in marine reference materials by HPLC-ICP-MS

Anion and cation exchange HPLC-ICP-MS was used to separate and detect mixtures of four dimethylarsinyl-riboside derivatives (arsenosugars), in the presence of eight other arsenic species naturally occurring in the marine environment. The separations achieved showed that two arsenosugars 11 and 13 (cf. Table 2) were present in shellfish certified reference materials (CRMs) and in a lobster hepatopancreas CRM. The concentration of the two arsenosugars in the shellfish samples amounts to 18% of the total arsenic as compared to arsenobetaine at 9–13% and dimethylarsinate at 4–9% of the total arsenic. Additionally, a chromatographic peak with the same retention time as that of 2-dimethylarsinylacetic acid was detected in the shellfish samples. Further support of the identity of this peak was gained after spiking the sample extracts with the standard substance which resulted in a single, but larger peak. The indication that this novel arsenical is present in shellfish, and the recently reported finding of arsenocholine in seafood supports a proposed marine biosynthetic pathway of arsenic that includes both of these compounds as the immediate precursors of arsenobetaine, the end-product of the marine arsenic metabolism.     

Trace and minor elements in four commercial honey brands

Instrumental neutron activation analysis was used to measure the concentrations of 24 elements in four honey brands commercially available in Austin, Texas (USA). The measured elements (and concentration) were: As, (<30 ng/g); Ba, (<2 g/g); Br, (0.24–0.49 g/g); Ce, (<20 ng/g); Co, (9–180 ng/g); Cr, (37–64 ng/g); Cs, (<3–45 ng/g); Fe, (<4–15.9 g/g); Hf, (<3 ng/g); Hg, (1 ng/g); K, (91–230 g/g); La, (<4 ng/g); Na, (20.3–25.3 g/g); Ni, (0.39–0.77 g/g); Rb, (68–340 ng/g); Sb, (13–61 ng/g); Sc, (<0.3–200 ng/g); Se, (<20 ng/g); Sm, (<9 ng/g); Sr, (<2 ng/g); Th, (<4 ng/g); U, (<30 ng/g); Zn, (3.36–4.61 g/g); and Zr, (<0.5–0.84 g/g). The results obtained were compared to the concentration of the same elements in honey produced or commercially available in Turkey, Mexico, El-Salvador, China, Czechoslovakia and Yugoslavia.     

Properties and applications of polyacrylacylisothiourea chelating fiber for preconcentration and separation of trace titanium, vanadium and bismuth

An ICP-OES method using a new poly-acrylacylisothiourea chelating fiber to preconcentrate and separate trace Ti(IV), V(V) and Bi(III) ions from solution samples is established. The results show that 5–25 ng/ml of Ti or V and 50–250 ng/ml of Bi ions in 200–1000 ml of solution can be enriched quantitatively by 0.05 g of the fiber at pH 3 with recoveries over 97%. These ions can be desorbed quantitatively with 10 ml of 4M HC1O₄. 100- to 1000-fold excesses of Fe(III), Al(III), Ca(II), Mg(II), Cu(II), Ni(II) and Mn(II) ions cause little interference. The chelating fiber stored for about 2 years can still be used repeatedly for preconcentration and separation of trace Ti, V and Bi ions from solution with above 95% recovery. The RSDs for enrichment and determination of 5 ng/ml of Ti or V and 50 ng/ml of Bi are in the range 2.5–2.8%. The recoveries of added standard in real waste waters and mineral samples are between 96 and 100%, and the concentration found for each ion in the mineral sample was in good agreement with that measured by ETAAS.     

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.     

Indirect determination of arsenic by flotation spectrophotometry

An indirect method of arsenic determination in the submicrogram range via the determination of molybdenum is presented here. High sensitivity is achieved by combination of the chemical amplification during formation of dodecamolybdoarsenic acid (arsenic: molybdenum ratio 1 12) with multiplication due to the formation of ion-association complexes during flotation-spectrophotometric molybdenum determination with crystal violet (molar ratio 1 2). Thus, the amplification factor relating to arsenic is 24.Dodecamolybdoarsenic acid is formed in a weakly acidic medium and is quantitatively extracted byn-butanol. Back extraction of the heteropoly acid to the aqueous phase and its simultaneous destruction provides the basis for the reaction of released molybdate ions with thiocyanate ions. The molybdenum-thiocyanate complex forms a sparingly soluble ion-association complex with crystal violet which can be floated with toluene on the phase boundary (film flotation). After separation of the aqueous phase the floated molybdenum compound is dissolved in acetone and the resulting free crystal violet ions are subjected to photometric determination at 590 nm as equivalent of the concentration of arsenic. The molar absorptivity of crystal violet is 3.2 · 10⁵1 · mol^–1 · cm^–1. Beer's law is obeyed in a concentration range from 0.01 to 1 g Mo · ml^–1 (0.001–0.1 g As · ml^–1). The resulting detection limit for arsenic is 1 ng · ml^–1.