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Analytical and Bioanalytical Chemistry (v.362, #5)
1998 Winter Conference on Plasma Spectrochemistry Scottsdale, Arizona, January 5–10, 1998
by Ramon M. Barnes (pp. 431-432).
Application of on-line HPLC-ICP-MS for the determination of the nuclide abundances of lanthanides produced via spallation reactions in an irradiated tantalum target of a spallation neutron source by W. Kerl; J. S. Becker; W. Dannecker; H.-J. Dietze (pp. 433-439).
An analytical procedure has been developed for the determination of spallation nuclides in an irradiated tantalum target using HPLC coupled on-line to ICP-MS after dissolution and separation of the tantalum matrix. Pieces of tantalum were taken from different locations of the irradiated tantalum target which had been used as the target material in a spallation neutron source. Tantalum was dissolved in a HNO3/HF mixture and the tantalum matrix was separated by liquid-liquid extraction so that only the spallation nuclides were left in the sample solutions. The major fraction of the spallation nuclides in the tantalum target are lanthanide metals in the μg g–1 concentration range determined in the present study. Additional reaction products are formed by the irradiation of trace impurities in the original tantalum target. The nuclide abundances of the lanthanide metals measured in the tantalum target differ significantly from the natural isotopic composition so that a lot of isobaric interferences of long-lived radionuclides and stable isotopes in the mass spectrum are to be expected. Therefore, all the lanthanide metals had to be separated chemically prior to their mass spectrometric determination. The separation of all rare earth elements was performed by ion chromatography on-line to ICP-MS. The nuclide abundances of each lanthanide were determined using a sensitive double-focusing sector field inductively coupled plasma mass spectrometer. The nuclide abundances of the lanthanides in the irradiated tantalum target calculated theoretically and the experimental results obtained by on-line HPLC-ICP-MS proved to be in good agreement.
The influence of molecular gases and analytes on excitation mechanisms in atmospheric microwave sustained argon plasmas by E. A. H. Timmermans; I. A. J. Thomas; J. Jonkers; E. Hartgers; J. A. M. van der Mullen; D. C. Schram (pp. 440-446).
The effect of introducing molecular compounds into argon plasmas has been studied using an expanding microwave induced plasma at atmospheric pressure. Besides the use of optical emission spectroscopy (OES), also the time dependent behavior of line intensities during power interruptions has been studied. From the measurements it is found that even an injection of small amounts of molecular compounds (> 0.5%) leads to important changes in excitation mechanisms in the plasma. It is also found that in the recombination zone downstream in the plasma an excitation mechanism which is independent of the electron density, e.g. excitation transfer from metastables or Penning ionization, must be responsible for the excitation of analytes.
Analytical selenoamino acid studies by chromatography with interfaced atomic mass spectrometry and atomic emission spectral detection by P. C. Uden; Susan M. Bird; Mihaly Kotrebai; Paula Nolibos; Julian F. Tyson; Eric Block; Eric Denoyer (pp. 447-456).
Consumption of selenium enriched plants or yeast-based nutritional supplements has been reported to provide anticarcinogenic benefits which are selenium compound dependent. Separation and identification of these selenium compounds is critical to understand the activity. Plants and yeast convert inorganic selenium in the soil or growth media into organoselenium compounds, probably following a route similar to the sulfur assimilatory pathway. Non-volatile selenium compounds produced include selenoamino acids, some of which have shown anticarcinogenic activity. Volatile compounds produced by chemical reaction of involatile precursors have also been found. An ion pair chromatographic method with ICP-MS detection for the separation of selenoamino acid standards potentially present in real samples is given. The method allows separation of selenoamino acids including such analytes as the cis-trans isomers of Se-1-propenyl-dl-selenocysteine. The method also provides the capability of determining the presence of selenoxides and possibly selenones, and tracking of other functionalities and reactions by selective derivatization. Alternatively, selenoamino acids are treated with ethylchloroformate to produce stable volatile derivatives which are amenable to GC separation with element specific atomic emission detection (GC-AED). Results of total selenium determination and speciation of selenium enriched yeast-based nutritional supplements, selenium enriched allium vegetables and bioremediation samples are presented.
Determination of trace and platinum-group elements in high ionic-strength volcanic fluids by sector-field inductively coupled plasma mass spectrometry (ICP-MS) by T. P. Fischer; S. Shuttleworth; P. A. O’Day (pp. 457-464).
The accurate measurement of ultra-trace concentrations of rare metals and platinum group elements in volcanic fluids is complicated by interferences, complex matrices, and preferential element partitioning. We analyzed condensed, high-temperature magmatic fluids collected from Kudryavy volcano (Kurile Islands, Russia) for Be, B, Rb, Sr, Mo, Ru, Rh, Pd, Cd, W, Re, Pt, Pb, Bi, and U using ICP-MS. The samples had three different matrices: 5 mol L–1 sodium hydroxide (NaOH, pH = 11), gas condensates of sulfuric acid (H2SO4, pH = 0), and solid elemental sulfur. Interferences and suppression/enhancement effects were investigated using standards in concentrated NaOH and H2SO4 solutions to determine adequate dilution for sample analyses, which then required very low levels of element detection (< 1 μg L–1 for most elements). Depending on the field sampling technique of volcanic gas vents, our results show significant differences in concentrations of some trace elements due to the precipitation of solid sulfur during gas condensation and variations in element volatility as a function of temperature.
Estimation of detection limits in inductively coupled plasma mass spectrometry by Evgeniy D. Prudnikov; R. M. Barnes (pp. 465-468).
The theoretical estimation of the detection limits in inductively coupled plasma mass spectrometry has been investigated. This calculation includes significant parameters of the ICP source and mass spectrometer. The calculated values show generally good agreement with experimental results. The development of a mathematical relationship may be useful for evaluation of instrumental parameters and sample introduction techniques.
Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization? by Heinz F. Falk; Bodo Hattendorf; K. Krengel-Rothensee; Nataly Wieberneit; Sarah L. Dannen (pp. 468-472).
An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. 62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards.
Dissolution of Al-Fe materials and analysis by inductively coupled plasma – atomic emission spectrometry by Assad S. Al-Ammar; R. M. Barnes (pp. 473-476).
A technique was developed for the dissolution of Al-Fe materials containing difficult to dissolve Al2O3. The developed procedure uses HCl and HNO3 for initial sample attack followed by digestion with a mixture of H3PO4 and H2SO4 at 200 °C. This procedure was employe to dissolve Al-Fe material samples before the determination of Al and Fe. Minor and trace elements (B, Cr, Cu, Mo, Si, Zr) were determined after dissolution in HCl and HNO3. Results of a round robin study verified the procedure accuracy. The developed methods have the required accuracy and precision to be used as a quality control procedure for Al-Fe materials analysis.
Application of a double-focusing magnetic sector inductively coupled plasma mass spectrometer with laser ablation for the bulk analysis of rare earth elements in rocks fused with Li2B4O7 by M. Ødegård; S. H. Dundas; B. Flem; A. Grimstvedt (pp. 477-482).
Results of the use of a double-focusing, magnetic sector inductively coupled plasma mass spectrometer (ICP-MS) with ultraviolet (UV) laser ablation (LA) are presented for the bulk analysis of rare earth elements (REEs) in rocks fused with Li2B4O7. The sample preparation procedure used a sample to flux weight ratio of 1 : 7, and was identical with a procedure routinely used for X-ray fluorescence (XRF) analyses of major and minor elements in geological materials. Calibration was based on a total of 18 international standard reference materials (SRMs), and Ba was used as an internal standard element for all REEs. The calibration curves were constructed using a weighted regression model. The use of internal standard, without exception, improved the correlation coefficients significantly. The 3σ detection limits were established by a blank sample of SiO2 spiked with Ba, and were in the range from 0.003 μg g–1 (159Tb) to 0.051 μg g–1 (140Ce). The use of a large set of SRMs for calibration gave a good basis for the evaluation of analytical quality, and extensive data for calculated analytical uncertainty are presented. Instrumental precision and the repeatability of the method were studied separately, and no significant difference in these two sets of parameters were found, indicating that the spread of results predominantly was connected to the instrumental measurements. Repeated ablations on the surface of a disk did not influence subsequent measurements with XRF, showing that the fused disks can be stored for future use in XRF and/or LA-ICP-MS analysis.
Total iodine in nutritional and biological reference materials using neutron activation analysis and inductively coupled plasma mass spectrometry by Yves Gélinas; G. Venkatesh Iyengar; R. M. Barnes (pp. 483-488).
In a recent collaborative study intended to extend the variety of reference materials certified for iodine, three mineralization methods were developed to quantify the total iodine content of biological and nutritional materials by inductively coupled plasma mass spectrometry (ICP-MS). A mixture of water-soluble tertiary amines was used as the matrix solution for two oxygen combustion methods and for a simple extraction at room temperature. Calibrations with matrix-matched standards, internal calibration, and isotope dilution with 129I were used. Good agreement between neutron activation analysis (NAA) and the two combustion methods was observed except for < 0.1 mg kg–1 iodine concentrations. The amine extraction method gave the most reliable results for the mixed diet, milk powder, and infant formula samples but low recoveries for other biological materials owing to an incomplete extraction and solubilization of iodine. The NAA method, with its freedom from reagent blank, is a useful technique for the independent determination of iodine in biological, environmental and food matrices, especially for verification of iodine results obtained by ICP-MS.
Simplified derivatization method for the speciation analysis of organolead compounds in water and peat samples using in-situ butylation with tetrabutylammonium tetrabutylborate and GC-MIP AES by Monika Heisterkamp; F. C. Adams (pp. 489-493).
A simplified derivatization method for the speciation analysis of organolead compounds in environmental samples followed by gas chromatography-microwave induced plasma atomic emission detection is developed. An in-situ butylation using tetrabutylammonium tetrabutylborate in an acetate buffer medium of pH 4.0 with simultaneous extraction of the derivatized organolead species into hexane was performed; for the analysis of the peat samples, the desorption of the different species from the matrix by acid leaching was also included. Detection limits at the sub-ng L–1 range, comparable to those achieved by Grignard-alkylation, were obtained for the different species. The accuracy of the method was confirmed by analysis of a standard reference material (BCR-CRM 605, road dust). Examples of applications for the analysis of tap water and peat are given.
Determination of lead concentration and lead isotope ratios in calcium supplements by inductively coupled plasma mass spectrometry after high pressure, high temperature digestion by Dula Amarasiriwardena; Kamal Sharma; R. M. Barnes (pp. 493-497).
The presence of lead as a contaminant in calcium supplements has aroused considerable public health interest in recent years. In this investigation lead and lead isotope ratios were determined by ICP-MS in ten brands of calcium supplements after high pressure/temperature digestion. Calcium supplements (200 to 250 mg) were digested in 2 mL of nitric acid at 230 °C and at a pressure of 1770 psi (1.2 × 104 kPa). Lead concentrations were determined by matrix-matched lead standards prepared in a high-purity calcium carbonate matrix. Good recoveries of lead and calcium were obtained for certified animal bone reference material. High levels of Pb (8 to 28 μg Pb per g of calcium) were found in calcium supplements that contain dolomite or bone meal. Chelated and refined calcium supplements had lower Pb levels (0.8 to 0.9 μg Pb/g Ca). Application of lead isotope ratios to distinguish the origin of calcium sources was also explored.
Development and application of liquid and gas-chromatographic speciation techniques with element specific (ICP-MS) detection to the study of anaerobic arsenic metabolism by E. B. Wickenheiser; K. Michalke; C. Drescher; A. V. Hirner; R. Hensel (pp. 498-501).
Following the observation of volatile hydride and methylated arsenic species in the gases released from sewage treatment facilities and municipal landfills, we have developed a method for investigating the production of such gases by an anaerobic organism. Here we report the application of high performance ion chromatography (HPIC), hydride generation gas chromatography (HG-GC), and purge and trap gas chromatography (PT-GC), coupled with inductively-coupled plasma mass spectrometry (ICP-MS) to study the formation of ionic and volatile arsenic compounds produced in a batch culture of the anaerobic methanogen Methanobacterium formicicum. In this time course experiment we observed arsenite, mono- and dimethylated arsenic acid, arsine, mono-, di- and trimethylarsine, as well as a currently unknown volatile arsenic species.