Rapid determination of selenium in various marine species by instrumental neutron activation analysis

Instrumental neutron activation analysis was used to determine selenium concentrations in several marine organisms including two certified reference materials /NRCC lobster hepatopancreas, NBS oyster tissue/ and one uncertified material /IAEA fish homogenate/. The⁷⁶Se/n, /^77mSe/T=17.4 s/ reaction was successfully employed to achieve an overall precision between 3–10% and detection limits between 0.3–0.6 g/g. The accuracy of the results, as compared to the certified values, was in excellent agreement with the NBS material and only slightly lower /9%/ for the NRCC material.     

Development, production and certification of microbiological reference materials

Since 1986 the National Institute of Public Health and Environmental Protection (RIVM) in the Netherlands has been developing and testing reference materials (RMs) for use in the field of water and food microbiology within the framework of the Measurements and Testing Programme (former BCR) of the European Union. The materials consist of gelatin capsules filled with artificially contaminated spray dried milk. Individual and collaborative studies on stability and homogeneity of the materials are described. The positive results obtained are followed by certification studies on certain reference materials. The results of two certification studies have now satisfactorily been completed, and certified values, related to the methods used, have been given for two certified reference materials (CRMs) containing the bacterial strains Salmonella typhimurium (5 cfp/capsule) and Enterococcus faecium (500 cfp, capsule), respectively. Two other RMs containing Bacillus cereus and Enterobacter cloacae will be certified by the end of 1994.     

k0-NAA quality assessment by analysis of different certified reference materials using the KAYZERO/SOLCOI software

A suite of natural matrix reference materials (RMs) were used to assess the quality of analytical results obtained by k ₀-instrumental neutron activation analysis (k ₀-INAA) at the Joef Stefan Institute (IJS). Five certified reference materials (CRMs) from the Institute for Reference Materials and Measurements (IRMM), two standard reference materials (SRMs) from the National Institute of Standards and Technology (NIST), three RMs from the International Atomic Energy Agency (IAEA) and one RM from IJS were analyzed. Altogether, results for twenty-four elements in inorganic matrices and twenty-nine elements in organic matrices, obtained by k ₀-INAA, were compared to certified values. Results obtained show good agreement with certified or assigned values except for Fe, La, Nd, Sm and U in inorganic matrices, and Ag, Al and Cr in organic matrices.     

Neutron flux and associated k0 parameters in the RPI after the last configuration change

The Portuguese Research Reactor (RPI) is a 1 MW swimming pool type reactor, operating since the early 1960s. The fuel is MTR type, with flat plates of U-Al alloy enriched to 93% in ²³⁵U. As the core configuration changed in April 2000, it became essential to characterise the neutron field in the most useful irradiation positions of RPI, in order to guarantee the accuracy in the application of k ₀-neutron activation analysis (k ₀-NAA). Experimental values of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from the 1/E shape (a) were determined using the Cd-ratio for multi-monitor method. The neutron temperature (T _n) was obtained from co-irradiation of Lu with 1/v monitors. The results for several irradiation positions are presented and discussed in this work. Some element concentrations are determined based on the parameters obtained in this work, and compared with the certified reference material concentrations.     

Determination of Uranium and Thorium Isotope Ratios by Inductively Coupled Plasma Mass Spectrometry

Measurement conditions were selected and a procedure was proposed for determining the ²³⁴U/²³⁸U and ²³⁰Th/²³²Th isotope ratios using an ELEMENT single-channel double-focusing inductively coupled plasma mass spectrometer. The procedure was tested in analyzing bottom sediments from Lake Baikal with the extraction preconcentration of uranium and thorium. The accuracy of the procedure was verified using certified reference materials and a model solution by comparing the results obtained with the data of spectrometry.     

Determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell

A method is described for determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell (ID–ICP–ORCMS). Sediment samples were digested with HNO₃, HClO₄, and HF, and the digestion included an elaborate evaporation process to remove bromine from the digested solution. Simple strong cation-exchange disk filtration was used to remove rare earth elements (REE) from the digested solution, because REE²⁺ seriously interfere with Se isotopes (i.e. ¹⁵⁶Gd²⁺ with ⁷⁸Se⁺, ¹⁶⁰Gd²⁺ with ⁸⁰Se⁺). Addition of acetic acid to the filtrate was examined to improve the sensitivity of ICP–ORCMS measurement of Se⁺ by means of a carbon-enhancement effect. The interfering for selenium isotopes were almost eliminated by use of H₂ as reaction gas. Interference from BrH⁺ formed in the reaction cell was negligible because the Br was removed in the evaporation process. Approximately 99.5% of REE were removed by cation-exchange disk filtration yet more than 99% of Se remained in the filtrate solution. The intensity for Se⁺ was enhanced approximately fourfold by addition of 5% (v/v) of acetic acid whereas that for was barely enhanced. Measured ⁸⁰Se/⁷⁸Se ratios in unspiked digested solutions of the sample were in good agreement with that for an Se standard solution. The analytical results for Se in the certified reference materials MESS-3 and PACS-1 were in good agreement with their certified values, with small uncertainties.      

New methods for acceleration of meat sample preparation prior to determination of the metal content by atomic absorption spectrometry

Focused microwave-assisted digestion and ultrasound leaching have been applied for the extraction of Pb, Cd, Cr, Cu, Fe, Zn, Ca, and Mg from raw meat. Semimembranous muscle (SM) of raw pig ham was used for optimizing both the digestion and extraction steps by multivariate approaches. The detection and quantification limits were 0.5 and 0.9 g kg^–1 for Pb, 0.06 and 0.1 g kg^–1 for Cd, 0.2 and 1.2 g kg^–1 for Cr, 0.4 and 3 g kg^–1 for Cu, 0.04 and 0.1 mg kg^–1 for Fe, 0.012 and 0.017 mg kg^–1 for Zn, 0.3 and 0.4 mg kg^–1 for Ca, and 0.01 and 0.03 mg kg^–1 for Mg. The precision, expressed as relative standard deviation (RSD), ranged between 2.5 and 9.6% for focused microwave-assisted digestion and between 3.5 and 10.6% for ultrasound leaching. The methods were then compared with a reference method and applied to a certified reference material (bovine muscle 184, from the BCR). The t-test, applied to the results obtained from focused microwave-assisted digestion, revealed that they are in agreement (p>0.01) with the certified and estimated values in the case of Pb, Cd, Cr, Cu, Fe, Ca, Mg, and Zn but not in that of Fe. In the case of ultrasound leaching, only the extraction of Pb, Cu, and Ca was quantitative. The method based on microwave digestion provides more accurate and precise results than ultrasound leaching. These new procedures have many advantages with regards to conventional methods, namely, reduction of the extraction time, simplification of the process, avoidance of chemical emissions to the atmosphere, and no losses of metals by volatilization.     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Trace determination of nickel (and cobalt) in biological reference materials by radiochemical neutron activation analysis

Summary Very few biological reference materials are certified for nickel below 1 mg · kg^–1. Neutron activation analysis was only rarely considered as a possible approach; reported sensitivities were usually not very good, unless preconcentration was applied.In the present work, the relatively high fast neutron flux of our TRIGA reactor was used to induce the ⁵⁸Ni(n, p)⁵⁸Co reaction, and ⁵⁸Co (E =811 keV) was radiochemically separated from other radionuclides by classical anion-exchange chromatography in hydrochloric acid. ⁵⁷Co was added to the irradiated sample before decomposition as a radioisotopic yield monitor. By concentrating the final sample fraction and measurement in a well-type HP Ge detector, Ni concentrations down to the 10-g · kg^–1 level could be determined for samples irradiated for 1 day. ⁶⁰Co, produced by neutron capture on ⁵⁹Co, is also coseparated and quantified from the gamma spectrum, so that both elements Ni and Co are determined. Results are reported for a series of NBS and other biological reference materials in the concentration range 10 g-10 mg · kg^–1. Possibilities for further increases in sensitivity are discussed.

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Spurenbestimmung von Nickel (und Cobalt) in biologischen Referenzmaterialien durch radiochemische Neutronenaktivierungsanalyse

     

Determination of subnanomolar concentrations of cobalt by adsorptive stripping voltammetry at a bismuth film electrode

Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10^–10 to 2 × 10^–8 mol L^–1. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10^–9 mol L^–1 was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10^–11 mol L^–1. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples.     

The instrumental determination of cadmium in biological samples at nanogram levels with the aid of a Compton suppression system and epithermal neutron activation analysis

Instrumental epithermal neutron activation analysis in conjunction with Compton suppression methods has been used to determine cadmium concentrations in seven biological reference materials. The¹¹⁴Cd(n, )¹¹⁵CD(t_1/2=53.3h^115mIn(t_1/2=4.5h) reaction using the 336.3 keV photopeak was successfully employed to achieve an overall precision between 4%–15% and detection limits between 10–20 ng/g. The accuracy of the results as compared to the certified or compilation values was in excellent agreement.     

Solid phase extraction of Cd(II), Pb(II), Zn(II) and Ni(II) from food samples using multiwalled carbon nanotubes impregnated with 4-(2-thiazolylazo)resorcinol

Multiwalled carbon nanotubes were impregnated with 4-(2-thiazolylazo)resorcinol and used for the separation and preconcentration of Cd(II), Pb(II), Zn(II) and Ni(II) ions from food samples. The analytes were quantitatively recovered at pH 7.0 and eluted with 3?mol?L^?1 acetic acid. The effects of pH value, flow rate, eluent type and sample volume on the recoveries, and the effects of alkali, earth alkali and transition metals on the retention of the analytes were studied. The method was validated using the standard certified reference materials SRM 1570A (spinach leaves) and IAEA 336 (lichen), and the results were found to be compatible with the certified values of reference materials. The new enrichment procedure was applied to the determination of these ions in various food samples.

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Isotope dilution ICP-MS with laser-assisted sample introduction for direct determination of sulfur in petroleum products

Inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) with direct laser-assisted introduction of isotope-diluted samples into the plasma, using a laser ablation system with high ablation rates, was developed for accurate sulfur determinations in different petroleum products such as sulfur-free premium gasoline, diesel fuel, and heating oil. Two certified gas oil reference materials were analyzed for method validation. Two different ³⁴S-enriched spike compounds, namely, elementary sulfur dissolved in xylene and dibenzothiophene in hexane, were synthesized and tested for their usefulness in this isotope dilution technique. The isotope-diluted sample was adsorbed on a filter-paper-like material, which was fixed in a special holder for irradiation by the laser beam. Under these conditions no time-dependent spike/analyte fractionation was only observed for the dibenzothiophene spike during the laser ablation process, which means that the measured ³⁴S/³²S isotope ratio of the isotope-diluted sample remained constant—a necessary precondition for accurate results with the isotope dilution technique. A comparison of LA-ICP-IDMS results with the certified values of the gas oil reference materials and with results obtained from ICP-IDMS analyses with wet sample digestion demonstrated the accuracy of the new LA-ICP-IDMS method in the concentration range of 9.2 g g^–1 (sulfur-free premium gasoline) to 10.4 mg g^–1 (gas oil reference material BCR 107). The detection limit for sulfur by LA-ICP-IDMS is 0.04 g g^–1 and the analysis time is only about 10 min, which therefore also qualifies this method for accurate determinations of low sulfur contents in petroleum products on a routine level.This article is dedicated to Wilhelm Fresenius who has continuously supported the academic career of Klaus G. Heumann and the analytical work of his group.     

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L^–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L^–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g^–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g^–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g^–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

Determination of trace amounts of gold in acid-attacked environmental samples by atomic absorption spectrometry with electrothermal atomization after preconcentration

A method for determination of trace amounts of gold in environmental samples (rocks, soils, sediments, and waters) by atomic absorption spectrometry with electrothermal atomization (ETAAS) after preconcentration using a chelating sorbent Spheron Thiol 1000 is described. The method accurately determines gold between 0.001 and several tens of grams per ton in samples having complex variations in mineralogy. Pulverized samples are roasted at 650°C to oxidize any sulfide and/or carbonaceous material. Samples are then subjected to a series of acid treatments to eliminate any silica matrix and to dissolve the sample. The Spheron Thiol 1000 is added to the sample solution, and then with sorbed gold is filtered out, washed, and ignited at 550°C. The residue is dissolved in aqua regia, evaporated, dissolved in distilled water, transferred to a volumetric flask, and analyzed by ETAAS.The limits of detection of gold, based on the 3 definition, were 0.5 ng g^–1 for 10-g samples (rocks, sediments, soils) and 0.05 ng mL^–1 for 1-L water samples. Precision of determination expressed by the relative standard deviation varied from 2.9% to 16.4%. The accuracy of the method is verified by analysis of certified reference materials. The obtained analytical results are in good agreement with attested values. The developed method was applied for gold determination in environmental samples affected by the acidification (acid mine drainage which is mainly a product of pyrite oxidation) from an open quartzite mine in the obov region situated NE of the city of Banská tiavnica (Slovakia).     

Low-temperature electrothermal vaporization of thenoyltrifluoroacetone complex of Sc(III) and Y(III) for sample introduction in an inductively coupled plasma atomic emission spectrometry,and their determination in biological samples

A new method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace Sc and Y, based on gaseous compound introduction into the plasma as their thenoyltrifluoroacetone (TTA) complexes by electrothermal vaporization was developed. Using the reagent TTA as chemical modifier can not only enhance the analytical signals, but also reduce the vaporization temperature. At a temperature of 1,000 °C the trace Sc and Y can be vaporized completely into ICP. The factors affecting the formation of the chelate and its vaporization behavior, such as drying time, vaporization temperature/time, reaction medium and the amount of TTA, were investigated in detail. Under the optimized conditions (drying temperature/time 100 °C/10 s, vaporization temperature/time 1,000 °C/4 s), the limits of detection for Sc and Y were 19 pg and 34 pg (3), respectively, and the relative standard deviations for Sc and Y were 4.2% (c _Sc=0.2 g mL^–1; n=7) and 2.6% (c _Y=0.5 g mL^–1; n=7). The linear ranges of the calibration graphs cover three orders of magnitude. The method was applied to the analysis of the biological reference materials (GBW 07602, bush branches and leaves; GBW 07604, poplar leaves), and the results obtained were in good agreement with the certified values.     

An ion-imprinted thiocyanato-functionalized mesoporous silica for preconcentration of gold(III) prior to its quantitation by slurry sampling graphite furnace AAS

A gold(III)-imprinted thiocyanato-functionalized silica network of type SBA-15 was prepared by co-condensation of tetraethoxysilane (TEOS) with thiocyanatopropyltriethoxysilane (TCTES) in the presence of Pluronic123 and Au(III) ions. Compared to the non-imprinted material, the imprint has a higher selectivity and adsorption capacity for Au(III). The maximum static adsorption capacity for Au(III) is 475 mg·g^?1 for the ion-imprinted, and 62 mg·g^?1 for the non-imprinted sorbent. The imprint was applied to the sorption of Au(III) from digested geological samples prior to its determination by graphite furnace atomic absorption spectrometry. Adsorption is fast and does not substantially prolong the analytical procedure. Under optimum conditions, the detection limit for Au(III) is 2 ng·g^?1. The method was validated by analyzing certified reference materials, and results were in good agreement with certified values. The procedure was successfully applied to the separation and determination of gold in complex geological samples.

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Graphical abstract Schematic presentation of the preparation of ion-imprinted thiocyanato-functionalized mesoporous silica and its application for the preconcentration of gold from digested soils before its determination by slurry sampling graphite furnace atomic absorption spectrometry (GF AAS).

     

Determination of hafnium and zirconium in geological materials by neutron activation analysis

In this work, neutron activation analysis was applied to analyze the geological standard materials: GSP-1 and W-1 from USGS, GB-1 and BB-1 from the University of Bahia, Brazil and a sample of uraniferous rock. Hf was determined by instrumental method and the obtained results was shown with relative standard deviations varying from 1.1 to 14%. In the case of Zr analyses, both instrumental and radiochemical neutron activation analyses were used. The interference of¹⁵⁴Eu radioisotope that emits -rays too close to those emitted by⁹⁵Zr was eliminated by retention of Zr in an anionic exchange resin column. The contribution of uranium fission product was considered in the Zr determination by using an interference factor. Results of Zr were presented with relative standard deviations varying from 2.0 to 25.7%. More precise results were obtained by using radiochemical separation. The concentration obtained for Hf and Zr in reference materials agreed well with respective certified values or information values.