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Analytical and Bioanalytical Chemistry (v.370, #5)
5th Symposium on “Mass Spectrometric Methods of Trace Element Analysis” and 16th ICP–MS Users Meeting, 18–21 September 2000 at Research Centre Jülich, Germany
by J. S. Becker (pp. 439-441).
The potential of inorganic mass spectrometry in mineral and trace element nutrition research by T. Walczyk (pp. 444-453).
Over the past two decades, new applications of inorganic mass spectrometry have been made possible by the use of stable isotopes as tracers in studies of mineral and trace element metabolism in man. Stable isotope techniques and radioisotope methods are the only reliable tools available for determination of the absorption, retention, or utilization of a nutrient by the human body. Recent developments in inorganic mass spectrometry might open new perspectives as progress in this field of research depends mainly on improving existing stable isotope techniques and on developing novel concepts. By improving precision in isotope analysis, isotope doses in experiments on man can be reduced to physiologically more meaningful levels. This will also enable reduction of the (often substantial) costs of isotopically labeling a nutrient in a test meal. Improvements in the mass spectrometric sensitivity will enable the development of new tracer techniques that have the potential to provide the information required by:1. governmental institutions for designing food fortification programs;2. the food industry for developing nutrient-fortified food products; and3. public health authorities for establishing reliable dietary recommendations for intake of inorganic nutrients.In this context the current scope and limitations of thermal ionization mass spectrometry, inductively coupled mass spectrometry, accelerator mass spectrometry, and resonance ionization mass spectrometry are evaluated. Iron isotopic variations in the human body are discussed as a possible source of bias that might be a future biological limit to stable isotope-dose reduction in experiments on iron metabolism in man.
Reaction chemistry and collisional processes in multipole devices for resolving isobaric interferences in ICP–MS by D. R. Bandura; V. I. Baranov; S. D. Tanner (pp. 454-470).
A low-level review of the fundamentals of ion-molecule interactions is presented. These interactions are used to predict the efficiencies of collisional fragmentation, energy damping and reaction for a variety of neutral gases as a function of pressure in a rf-driven collision/reaction cell. It is shown that the number of collisions increases dramatically when the ion energies are reduced to near-thermal (< 0.1 eV), because of the ion–induced dipole and ion–dipole interaction. These considerations suggest that chemical reaction can be orders of magnitude more efficient at improving the analyte signal/background ratio than can collisional fragmentation. Considerations that lead to an appropriate selection of type of gas, operating pressure, and ion energies for efficient operation of the cell for the alleviation of spectral interferences are discussed. High efficiency (large differences between reaction efficiencies of the analyte and interference ions, and concomitant suppression of secondary chemistry) might be required to optimize the chemical resolution (determination of an analyte in the presence of an isobaric interference) when using ion-molecule chemistry to suppress the interfering ion. In many instances atom transfer to the analyte, which shifts the analytical m/z by the mass of the atom transferred, provides high chemical resolution, even when the efficiency of reaction is relatively low. Examples are given of oxidation, hydroxylation, and chlorination of analyte ions (V+, Fe+, As+, Se+, Sr+, Y+, and Zr+) to improve the capability of determination of complex samples. Preliminary results are given showing O-atom abstraction by CO from CaO+ to enable the determination of Fe in high-Ca samples.
Potential of mass spectrometry for the analysis of inorganic high-temperature vapors by K. Hilpert (pp. 471-478).
Mass spectrometry is the most versatile method for the analysis of high-temperature vapors, because it enables the identification of the gaseous species and the determination of their partial pressures. If the vaporization processes are conducted under thermodynamic equilibrium, thermodynamic data can be evaluated from the partial pressures and their temperature-dependencies. The mass spectrometric methods used for the determination of thermodynamic data of high-temperature vapors are Knudsen effusion mass spectrometry (KEMS), transpiration mass spectrometry (TMS), and laser-induced vaporization mass spectrometry (LVMS). KEMS is used whenever possible. Limitations of KEMS and TMS are the container problem, which limits the measurement temperatures to approximately 2500 K. The container problem is overcome by LVMS, which enables measurements up to approximately 7000 K. The upper limit of the partial pressure measurement by KEMS of approximately 10 Pa does not apply for TMS, which enables measurements up to pressures of approximately 0.1 MPa. The fundamentals of the different methods are described and results are presented. Emphasis is on KEMS.
Thorium and iodine memory effects in inductively-coupled plasma mass spectrometry by Assad Al-Ammar; E. Reitznerová; R. M. Barnes (pp. 479-482).
Thorium and iodine memory effects have been characterized experimentally for inductively-coupled plasma mass spectrometry by adding ammonia gas directly to the spray chamber and nebulizing aqueous ammonia sample solutions to assess analyte memory retention sites. Thorium memory effect originates from the tendency of an unidentified thorium compound to volatilize from the spray-chamber walls, and not from Th compound adsorption to nebulizer tubing. The mass spectrometer skimmer and sampler cones, ion optics, quadrupole, and other components are not responsible for the memory effect. Unlike that of thorium the iodine memory effect originates from adsorption of iodine compounds on nebulizer tubing surfaces and from volatilization of HI and I2 from the spray-chamber walls. Addition of ammonia sample solutions or ammonia gas directly to the spray chamber eliminated the Th and I memory effects in practical analyses, and blank levels were achieved after 2 min wash-outs. Quantitative recoveries were obtained for Th and I in reference materials.
Experimental evidence for the formation of doubly charged oxide and hydroxide ions in inductively coupled plasma mass spectrometry by B. Hattendorf; D. Günther (pp. 483-487).
The formation of doubly charged polyatomic ions in inductively coupled plasma mass spectrometers was investigated using commercially available instruments. The species observed were ThO2+ and ThOH2+, which were found in similar amounts with the different instruments used in this study, when operated under routine analytical conditions. The signal ratios for ThO2+ were between 1.8 × 10–4 and 4.2 × 10–4 relative to the singly charged elemental ion and between 1.4 × 10–2 and 2.2 × 10–2 relative to the doubly charged elemental ion. The formation of ThOH2+ was between 1.1 × 10–4 and 2.8 × 10–4 relative to the singly charged elemental ion and between 0.72 × 10–2 and 1.3 × 10–2 relative to the doubly charged elemental ion. A mechanism is proposed for the formation of the doubly charged oxide and hydroxide ions that is based on the condensation of the doubly charged elemental ion with water or oxygen molecules in the interface region of the mass spectrometer.
Removal of interfering elements in ICP–QMS for the determination of Pt, Rh, and Pd by chemically modified sample introduction capillaries by H.-G. Riepe; V. Loreti; R. Garcia-Sanchez; C. Cámara; J. Bettmer (pp. 488-491).
New on-line methods developed for the determination of Pt, Rh, and Pd by inductively coupled plasma– quadrupole mass spectrometry (ICP–QMS) include separation of elements which might lead to spectral interference in the quadrupole instrument. The fused-silica capillaries generally used for transport of the sample to μ-flow nebulizers have been chemically modified with ion-exchanger compounds to remove interfering elements such as Cu, Pb, or Hf. Characterization of the modification procedures by atomic-force microscopy showed that the quality of the quartz material and the kind of modification had a decisive influence on the yield of surface modification, and thus the exchange capacity of the capillaries.
SI-traceable certification of the amount content of cadmium below the ng g–1 level in blood samples by isotope dilution ICP–MS applied as a primary method of measurement by J. Diemer; J. Vogl; C. R. Quétel; T. Linsinger; P. D. P. Taylor; A. Lamberty; J. Pauwels (pp. 492-498).
The development and implementation of a method for the certification of cadmium in blood samples at low ng g–1 and sub ng g–1 levels is described. The analytical procedure is based on inductively coupled plasma isotope dilution mass spectrometry (ICP–IDMS) applied as a primary method of measurement. Two different sample digestion methods, an optimized microwave digestion procedure using HNO3 and H2O2 as oxidizing agents and a high-pressure asher digestion procedure, were developed and compared. The very high salt content of the digests and the high molybdenum content, which can cause oxide-based interferences with the Cd isotopes, were reduced by a chromatographic matrix separation step using an anion-exchange resin. All isotope ratio measurements were performed by a quadrupole ICP–MS equipped with an ultrasonic nebulizer with membrane desolvator. This sample introduction set-up was used to increase sensitivity and minimize the formation of oxides (less MoO+ interference with the Cd isotopes).Because of the very low Cd concentrations in the samples and the resulting need to minimize the procedural blank as much as possible, all sample-processing steps were performed in a clean room environment. Detection limits of 0.005 ng g–1 Cd were achieved using sample weights of 2.7 g. The method described was used to re-certify the cadmium content of three different blood reference materials from the Community Bureau of Reference (BCR) of the European Commission (BCR-194, BCR-195, BCR-196). Cadmium concentrations ranged between ∼0.2 ng g–1 and ∼12 ng g–1. For these materials, SI-traceable certified values including total uncertainty budgets according to ISO and Eurachem guidelines were established.
Development of an electrothermal vaporization ICP–MS method and assessment of its applicability to studies of the homogeneity of reference materials by K.-C. Friese; K.-H. Grobecker; U. Wätjen (pp. 499-507).
A method has been developed for measurement of the homogeneity of analyte distribution in powdered materials by use of electrothermal vaporization with inductively coupled plasma mass spectrometric (ETV–ICP–MS) detection. The method enabled the simultaneous determination of As, Cd, Cu, Fe, Mn, Pb, and Zn in milligram amounts of samples of biological origin. The optimized conditions comprised a high plasma power of 1500 W, reduced aerosol transport flow, and heating ramps below 300 °C s–1. A temperature ramp to 550 °C ensured effective pyrolysis of approximately 70% of the organic compounds without losses of analyte. An additional hold stage at 700 °C led to separation of most of the analyte signals from the evaporation of carbonaceous matrix compounds.The effect of time resolution of signal acquisition on the precision of the ETV measurements was investigated. An increase in the number of masses monitored up to 20 is possible with not more than 1% additional relative standard deviation of results caused by limited temporal resolution of the transient signals. Recording of signals from the nebulization of aqueous standards in each sample run enabled correction for drift of the sensitivity of the ETV–ICP–MS instrument. The applicability of the developed method to homogeneity studies was assessed by use of four certified reference materials. According to the best repeatability observed in these sample runs, the maximum contribution of the method to the standard deviation is approximately 5% to 6% for all the elements investigated.
41Ca ultratrace determination with isotopic selectivity > 1012 by diode-laser-based RIMS by P. Müller; B. A. Bushaw; K. Blaum; S. Diel; Ch. Geppert; A. Nähler; N. Trautmann; W. Nörtershäuser; K. Wendt (pp. 508-512).
41Ca ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in 41Ca-radiodating. Depending on the application, 41Ca isotopic abundances in the range of 10–9 to 10–15 relative to the dominant stable isotope 40Ca must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of ∼ 5 × 1012 in the suppression of neighboring isotopes and > 108 for isobars, together with an overall detection efficiency of ∼ 5 × 10–5. Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting 41Ca/40Ca isotope ratios was better than 5%.
Investigations on the use of chemical modifiers for the direct determination of trace impurities in Al2O3 ceramic powders by slurry electrothermal evaporation coupled with inductively-coupled plasma mass spectrometry (ETV–ICP–MS) by M. C. Wende; J. A. C. Broekaert (pp. 513-520).
The direct determination of trace impurities in Al2O3 ceramic basic powders by ICP–MS using electrothermal evaporation (ETV) with slurry sampling has been investigated. To increase interference-free analyte volatilization, the use of the palladium-group modifiers (PGM) IrCl3, Pd(NO3)2, and PdCl2 for the determination of Ca, Fe, Ga, Mg, Mn, Na, Ni, and V in Al2O3 powders was studied. Their role, which in ETV–ICP–MS and ETV– ICP–OES is to stabilize the investigated analyte during the ashing phase, to increase vaporization of the matrix, and to reduce transport losses was investigated.Optimum analysis results were obtained with PdCl2 modifier when 500 ng Pd was used for a sample weight of 100 μg Al2O3 injected into the ETV. Calibration was performed by standard addition with aqueous solutions of the analytes. The RSDs calculated from triplicate analysis ranged form 5 to 10%. Detection limits between 0.07 μg g–1 (Ga) and 1.1 μg g–1 (Na) were achieved. The accuracy was proven for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V by analyzing an NIST standard reference Al2O3 material (SRM 699) with a middle grain size of 16.4 μm. The analytical method was used for the analysis of Al2O3 powder (AKP 30, Sumitomo, Japan) with impurities in the low μg g–1 range and a middle grain size of 1.1 μm. The results obtained for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V were comparable with those obtained by ICP–MS subsequent to conventional decomposition with hydrochloric acid at high pressure.
Determination of trace elements in quartz glass by use of LINA-Spark–ICP–MS as a new method for bulk analysis of solid samples by Markus Tibi; K. G. Heumann (pp. 521-526).
The determination of trace elements in pure quartz glass samples has been performed by coupling an ICP quadrupole mass spectrometer with the LINA-Spark-Atomizer, an IR laser ablation system dedicated to direct bulk and surface analysis of solid samples. Linear calibration curves were obtained for nine elements (Na, Al, Ca, Ti, Cr, Mn, Zr, Ba, and Pb) in the ng g–1 range with detection limits of less than 10 ng g–1 for Ca, Cr, Mn, Zr, Ba, and Pb and in the range of 120–220 ng g–1 for Na, Al, and Ti. The distance between the laser focal point and the sample surface has a significant influence on signal intensity and precision, both of which can be improved by a factor of approximately two by focusing the laser 15 mm behind the sample surface. Aerosol moistening reduced the standard deviation of the signal intensity by a factor of 2–4. Signal instability, which resulted from different ablation rates or variations in the transmission of the mass spectrometer, were compensated by use of the simultaneously measured SiAr+ ion as an internal standard. Under these conditions precision was usually better than 5% RSD. The results were compared with those obtained by use of a commercial LA–ICP–MS system. With this instrumentation linear calibration curves were achieved for three elements only (Al, Ti, and Pb), showing that LA–ICP–MS is less appropriate for bulk analysis in the ng g–1 range.
Determination of stoichiometry and concentration of trace elements in thin BaxSr1–xTiO3 perovskite layers by J. S. Becker; S. F. Boulyga (pp. 527-533).
This paper describes an analytical procedure for determining the stoichiometry of BaxSr1–xTiO3 perovskite layers using inductively coupled plasma mass spectrometry (ICP-MS). The analytical results of mass spectrometry measurements are compared to those of X-ray fluorescence analysis (XRF). The performance and the limits of solid-state mass spectrometry analytical methods for the surface analysis of thin BaxSr1–xTiO3 perovskite layers – sputtered neutral mass spectrometry (SNMS) – are investigated and discussed.
Trace analysis of high-purity graphite by LA–ICP–MS by Carola Pickhardt; Johanna Sabine Becker (pp. 534-540).
Laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) has been established as a very efficient and sensitive technique for the direct analysis of solids. In this work the capability of LA–ICP–MS was investigated for determination of trace elements in high-purity graphite. Synthetic laboratory standards with a graphite matrix were prepared for the purpose of quantifying the analytical results. Doped trace elements, concentration 0.5 μg g–1, in a laboratory standard were determined with an accuracy of 1% to ± 7% and a relative standard deviation (RSD) of 2–13%. Solution-based calibration was also used for quantitative analysis of high-purity graphite. It was found that such calibration led to analytical results for trace-element determination in graphite with accuracy similar to that obtained by use of synthetic laboratory standards for quantification of analytical results. Results from quantitative determination of trace impurities in a real reactor-graphite sample, using both quantification approaches, were in good agreement. Detection limits for all elements of interest were determined in the low ng g–1 concentration range. Improvement of detection limits by a factor of 10 was achieved for analyses of high-purity graphite with LA–ICP–MS under wet plasma conditions, because the lower background signal and increased element sensitivity.
Spark-source mass spectrometric assessment of silicon concentrations in silicon-doped gallium arsenide single crystals by B. Wiedemann; J. D. Meyer; D. Jockel; H. C. Freyhardt; B. Birkmann; G. Müller (pp. 541-543).
The spark-source mass spectrometric assessment of silicon concentrations in silicon-doped vertical-gradient-freeze gallium arsenide is presented. The silicon concentrations determined are compared with the charge-carrier densities measured by means of the Hall effect with van der Pauw symmetry along the axis of a single crystal.
Determination of rare earth elements in environmental matrices by sector-field inductively coupled plasma mass spectrometry by Jörgen Riondato; F. Vanhaecke; L. Moens; Richard Dams (pp. 544-552).
In the framework of an international certification campaign, sector-field inductively coupled plasma mass spectrometry (sector-field ICP–MS) was used for the accurate determination of the rare earth elements in five candidate reference materials: aquatic plant, calcareous soil, mussel tissue, river sediment, and tuna muscle. All samples were taken into solution by use of microwave-assisted or mixed microwave-assisted / open beaker acid digestion. Subsequently, the samples were appropriately diluted and subjected to ICP–MS analysis.Except for Sc, all the elements involved were determined at low mass resolution (R = 300). For Sc, application of a higher resolution setting (R = 3000) was required to separate the analyte signal from those of several molecular ions which gave rise to spectral overlap at low mass resolution. Some of the heavier REE can also suffer from spectral overlap attributed to the occurrence of oxide ions (MO+) of the lighter REE and Ba. This spectral overlap could be successfully overcome by mathematical correction. Matrix effects were overcome by use of two carefully selected internal standards, such that external calibration could be used. On each occasion, a geological reference material was analyzed as a quality-control sample and the reliability of all results obtained was additionally checked by means of chondrite normalization.For tuna muscle the content of all REE was below the limit of detection. For calcareous soil and river sediment, low to sub μg g–1 values were observed, whereas the REE content of aquatic plant and mussel tissue was considerably lower (low to sub ng g–1).Overall, the results obtained were in excellent agreement with the average values, calculated on the basis of all “accepted” values, obtained in different laboratories using different techniques.
Development of a procedure for the multi-element determination of trace elements in wine by ICP–MS by M. M. Castiñeira; R. Brandt; A. von Bohlen; N. Jakubowski (pp. 553-558).
An inductively coupled plasma mass spectrometric (ICP–MS) procedure has been developed for the determination of trace elements in wine. The procedure consists in simple 1+1 dilution of the wine and semi-quantitative analysis (without external calibration) using In as internal standard. Thirty-one elements at concentrations ranging from 0.1 mg mL–1 to 0.5 ng mL–1 can be determined by ICP–MS analysis with and without digestion. It was investigated whether a matrix effect observed for EtOH in the wine matrix can be overcome by application of a micro-concentric nebulizer with a membrane desolvator (MCN 6000). The results obtained for the MCN 6000 are compared with those obtained by use of a conventional Meinhard nebulizer. It is shown that the observed matrix effect can only be compensated by use of an internal standard for the Meinhard nebulizer, but not for the MCN 6000. Results for ICP–MS are compared with those obtained by total reflection X-ray fluorescence spectrometry (TXRF).
Analysis of Ir in Köfelsit rocks by inductively coupled plasma–sector-field mass spectrometry (ICP–SFMS) by Gunda Koellensperger; Stephan Hann; Günter Prinz; Gerhard Stingeder; Michael Bujatti-Narbeshuber (pp. 559-565).
Three different analytical strategies have been evaluated for the quantification of Ir in geological samples. Glassy rock samples from Köfels and reference material WGB-1 were analyzed directly by inductively coupled plasma sector field mass spectrometry (ICP–SFMS) at mass resolution 400 using membrane desolvation and at mass resolution 9500 without membrane desolvation. Matrix separation by anion-exchange pre-concentration was also investigated. The ultrasonic nebulizer USN6000AT+ (Cetac Technologies, Omaha, NE, USA) incorporating a membrane desolvation unit was used as the sample-introduction system. Sample preparation involved complete microwave-assisted acid digestion of the silicate matrix with HNO3–HCl–HF. The results obtained by the three methods of quantification were in good agreement, showing that oxide-type interferences were effectively eliminated solely by membrane desolvation. The limits of detection were 6 pg g–1 for low resolution measurement with use of the membrane, 15 pg g–1 at a mass resolution of 9500, and 59 pg g–1 for the ion-exchange procedure. The ultimate precision obtained for the Köfelsit Ir data was, however, compromised by the small sample intake (0.3 g), because of the inhomogeneous distribution of Ir in geological samples.
Recognizing heterogeneous distribution of platinum group elements (PGE) in geological materials by means of the Re–Os isotope system by T. Meisel; Johann Moser; Wolfhard Wegscheider (pp. 566-572).
The identification of uncertainties caused by sample inhomogeneity, as distinct from those caused by sample preparation and measurement, is a challenging task. Use of chemometric methods to separate and estimate these contributions to the combined standard uncertainty of a measurement (u c ) of an analytical result requires complex experiments. The difficulty of platinum group element measurement makes this task even more complex. But unless it can be demonstrated that sample inhomogeneity is the major contributor to the high variability of an analytical result one should be careful not to mistakenly attribute this to a nugget effect. In this contribution we are able to demonstrate in two special cases that irreproducible results (up to 90% RSD) for analysis of Os and Re in the pg g–1 to ng g–1 range are truly caused by a nugget effect and not by inadequacies of the analytical method.
Precise isotope-ratio measurements of lead species by capillary gas chromatography hyphenated to hexapole Multicollector ICP–MS by E. M. Krupp; Christophe Pécheyran; Simon Meffan-Main; Olivier F. X. Donard (pp. 573-580).
The precision and accuracy of lead isotope-ratio determination on a short transient signal has been assessed by coupling capillary gas chromatography to the Isoprobe (Micromass, UK), a single-focusing inductively coupled plasma mass spectrometer with multicollector detection. A T-piece connecting the GC transfer line to the torch enabled continuous aspiration of thallium solution for mass-bias correction. The volatile lead species PbEt4 was derivatized from NIST isotopic certified lead standard SRM 981 and different amounts of PbEt4 dissolved in iso-octane were injected into the GC. Chromatograms were recorded in multicollection mode by use of Faraday cups; seven isotopes (204Pb, 206Pb, 207Pb, 208Pb, 203Tl, 205Tl, and 202Hg) were monitored simultaneously at a transient resolution of 160 ms. PbEt4 peaks were obtained with a half-width of 1.2 s and a base width of 3.5 s. Lead isotope ratios were calculated from the peak areas integrated for each lead isotope, giving precision in the range of 0.02 to 0.07% for ratios of high-abundant isotopes and injections of 5 and 50 pg absolute amount as lead (five replicates). Mass bias was found to be about 0.5% per mass unit and was corrected by using the continuously measured thallium signals at 203Tl and 205Tl. After mass-bias correction, deviation of the certified lead ratio values was found to be in the range of 0.02 to 0.15% accuracy.
HPIC–UV–ICP–SFMS study of the interaction of cisplatin with guanosine monophosphate by S. Hann; A. Zenker; M. Galanski; T. L. Bereuter; G. Stingeder; B. K. Keppler (pp. 581-586).
Interaction of cis-[Pt(NH3)2Cl2] (cisplatin) with 5′-guanosine monophosphate (5′-GMP) has been investigated for the first time by on-line coupling of high performance ion chromatography (HPIC) to inductively coupled plasma sector field mass spectrometry (ICP–SFMS). The time-dependent reaction course of the cisplatin-5′-GMP system was followed after incubation under simulated physiological conditions by monitoring the decrease in the concentration of 5′-GMP and the increase in the concentration of formed adducts, on the basis of speciation analysis. Because of the two-step mechanism an intermediate mono adduct was observed together with the major product, the bis adduct cis-[Pt(NH3)2(GMP)2]2–. The data obtained correlated well with those from earlier studies employing orthogonal techniques such as capillary electrophoresis (CE). Furthermore, HPIC–ICP–SFMS provided unambiguous stoichiometric information about the major GMP-adduct. For this purpose the platinum-to-phosphorus ratio was determined by simultaneously measuring 31P and 195Pt. To separate significant interferences from 15N16O+, 14N16O1H+, 12C18O1H+, and 13C17O1H+ on 31P, high-mass resolution (m/Δm = 4500) proved to be mandatory. The P/Pt signal ratio of 2/1 obtained corresponds to the molar ratio in the bis adduct cis-[Pt(NH3)2(GMP)2]2–.
Species-specific isotope-ratio measurements of volatile tin and antimony compounds using capillary GC–ICP–time-of-flight MS by Karsten Haas; J. Feldmann; Rainer Wennrich; Hans-Joachim Stärk (pp. 587-596).
The analytical performance of an axial inductively-coupled-plasma time-of-flight mass spectrometer (ICP–TOFMS) as a detector for fast transient chromatographic signals resulting from the coupling to capillary gas chromatography (CGC) was investigated. A cryotrapping GC–ICP–TOFMS method for the determination of volatile metal(loid) compounds (VOMs) in gases was used and the suitability of the TOF mass analyzer for multi-elemental speciation analysis and multi-isotope ratio determinations was studied in terms of accuracy and precision. Isotope ratios 118Sn/120Sn and 121Sb/123Sb have been determined in in-house gas standard atmospheres in Tedlar bags at two different levels (100 pg and 1 ng) for different elemental species (SnH4, MeSnH3, Me2SnH2, Me3SnH, BuSnH3, SbH3, and MeSbH2). A limitation arising from counting statistics in both detection modes could be shown. A solution containing rhodium (10 ng mL–1) and cadmium (40 ng mL–1) was introduced simultaneously to the GC outlet. Rhodium acts as a continuous internal standard and Cd is used for mass-bias correction (by measuring the 111Cd/113Cd ratio). The detection system in both pulse counting and analog mode was examined. The best attainable precision was established for Me2SnH2 (analog mode, 12 replicates, 1 ng, RSD 0.34%, accuracy 0.31%) whereas most other species ranged between 0.4 and 0.5% RSD if higher concentrations were used. The limitations of the pulse counting system are clearly seen, with peak heights of more than 2000 counts reaching saturation (for an integration time of 100 ms), which reduces the accuracy of isotope ratio determinations. A dozen VOM could be detected in an aged landfill gas sample; several unidentified Sn compounds were present. Although their isotope ratios are within the confidence value of the standards, it is not yet clear if the acquired precision is good enough to identify isotopic fractionation of metal(loid)s through biovolatilization processes. With the precision achieved, the combination of cryotrapping GC and ICP–TOFMS is a powerful tool for monitoring volatile multi-element species in multi-tracer experiments and isotope dilution methodology.
Gas chromatography – inductively coupled plasma – time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental water samples by M. Heisterkamp; F. C. Adams (pp. 597-605).
The application of inductively coupled plasma – time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental waters is described. Construction of the transfer line was achieved by means of a relatively simple and rapid coupling procedure. Derivatization of the ionic lead species was achieved by in-situ propylation with sodium tetrapropylborate; simultaneous extraction of the derivatized compounds in hexane was followed by separation and detection by capillary gas chromatography hyphenated to inductively coupled plasma–time-of-flight mass spectrometry. Detection limits for the different organolead species ranged from 10 to 15 fg (as Pb), corresponding to procedural detection limits between 50 and 75 ng L–1, on the basis of a 50 mL snow sample, extraction with 200 μL hexane, and subsequent injection of 1 μL of the organic extract on to the column. The accuracy of the system was confirmed by additional analysis of the water samples by capillary gas chromatography coupled with microwave-induced plasma–atomic-emission spectrometry and the analysis of a standard reference material CRM 605 (road dust) with a certified content of trimethyllead.
Characterization of neutron transmuted zinc traces in pure copper materials by isotope dilution mass spectrometry by G. Wermann; D. Alber; W. Pritzkow; G. Riebe; W. Görner (pp. 606-611).
The neutron transmutation doping (NTD) of highly pure copper with zinc was investigated as a promising means of achieving controlled gradation of the zinc content in the range 1–20 μg g–1. The doping process leads to the enrichment of two stable isotopes 64Zn and 66Zn in a ratio which differs from that of natural isotopic distribution. Mass spectrometric investigations by thermal ionization mass spectrometry (TIMS) were performed to validate the results obtained by gamma spectrometry. The investigations included both determination of the isotopic ratios of the doped zinc isotopes and the analysis of the accumulated zinc contents by isotope dilution (ID) analysis. Thereby a sample-specific correction of the blank could be performed because the isotope 68Zn was not influenced, because of the transmutation process. The results obtained by TIMS prove the strict proportionality of the doped zinc content, in the range 5 to 20 μg g–1, to the neutron fluence. Comparison with gamma spectrometric results showed a very good agreement within the uncertainties.
Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry by Sergei F. Boulyga; J. Sabine Becker (pp. 612-617).
As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF–ICP–MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF–ICP–MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4×10–4 and 10–3 counts per atom were achieved for 238U in DF–ICP–QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2×10–4 and 1.4×10–4, respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 μg L–1 NBS U-020 standard solution was 0.11% (238U/235U) and 1.4% (236U/238U) using a MicroMist nebulizer and 0.25% (235U/238U) and 1.9% (236U/238U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/238U ratio ranged from 10–5 to 10–3. Results obtained with ICP–MS, α- and γ-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.
ICP–MS with hexapole collision cell for isotope ratio measurements of Ca, Fe, and Se by Sergei F. Boulyga; J. S. Becker (pp. 618-623).
To avoid mass interferences on analyte ions caused by argon ions and argon molecular ions via reactions with collision gases, an rf hexapole filled with helium and hydrogen has been used in inductively coupled plasma mass spectrometry (ICP–MS), and its performance has been studied. Up to tenfold improvement in sensitivity was observed for heavy elements (m > 100 u), because of better ion transmission through the hexapole ion guide. A reduction of argon ions Ar+ and the molecular ions of argon ArX+ (X = O, Ar) by up to three orders of magnitude was achieved in a hexapole collision cell of an ICP–MS (“Platform ICP”, Micromass, Manchester, UK) as a result of gas-phase reactions with hydrogen when the hexapole bias (HB) was set to 0 V; at an HB of 1.6 V argon, and argon-based ions of masses 40 u, 56 u, and 80 u, were reduced by approximately four, two, and five orders of magnitude, respectively. The signal-to-noise ratio 80Se/ 40Ar2 + was improved by more than five orders of magnitude under optimized experimental conditions. Dependence of mass discrimination on collision-cell properties was studied in the mass range 10 u (boron) to 238 u (uranium). Isotopic analysis of the elements affected by mass-spectrometric interference, Ca, Fe, and Se, was performed using a Meinhard nebulizer and an ultrasonic nebulizer (USN). The measured isotope ratios were comparable with tabulated values from IUPAC. Precision of 0.26%, 0.19%, and 0.12%, respectively, and accuracy of 0.13% 0.25%, and 0.92%, respectively, was achieved for isotope ratios 44Ca/ 40Ca and 56Fe/57Fe in 10 μg L–1 solution nebulized by means of a USN and for 78Se/80Se in 100 μg L–1 solution nebulized by means of a Meinhard nebulizer.
Isotope-ratio measurements of lead in NIST standard reference materials by multiple-collector inductively coupled plasma mass spectrometry by I. Platzner; S. Ehrlich; L. Halicz (pp. 624-628).
The capability of a second-generation Nu Instruments multiple collector inductively coupled plasma mass spectrometer (MC-ICP–MS) has been evaluated for precise and accurate isotope-ratio determinations of lead. Essentially the mass spectrometer is a double-focusing instrument of Nier–Johnson analyzer geometry equipped with a newly designed variable-dispersion ion optical device, enabling the measured ion beams to be focused into a fixed array of Faraday collectors and an ion-counting assembly. NIST SRM Pb 981, 982, and 983 isotopic standards were used. Addition of thallium to the lead standards and subsequent simultaneous measurement of the thallium and lead isotopes enabled correction for mass discrimination, by use of the exponential correction law and 205Tl/203Tl = 2.3875. Six measurements of SRM Pb-982 furnished the results 206Pb/204Pb = 36.7326(68), 207Pb/204Pb = 17.1543(30), 208Pb/204Pb = 36.7249(69), 207Pb/206Pb = 0.46700(1), and 208Pb/206Pb = 0.99979(2); the NIST-certified values were 36.738(37), 17.159(25), 36.744(50), 0.46707(20), and 1.00016(36), respectively. Direct isotope lead analysis in silicates can be performed without any chemical separation. NIST SRM 610 glass was dissolved and introduced into the MC-ICP–MS by means of a micro concentric nebulizer. The ratios observed were in excellent agreement with previously reported data obtained by TIMS and laser ablation MC-ICP–MS, despite the high Ca/Pb concentration ratio (200/1) and the presence of many other elements at levels comparable with that of lead. Approximately 0.2 μg lead are sufficient for isotope analysis with ratio uncertainties between 240 and 530 ppm.
Laser ablation inductively coupled plasma mass spectrometry: a new tool for trace element analysis in ice cores by H. Reinhardt; M. Kriews; H. Miller; O. Schrems; C. Lüdke; E. Hoffmann; J. Skole (pp. 629-636).
A new method for the detection of trace elements in polar ice cores using laser ablation with subsequent inductively coupled plasma mass spectrometry analysis is described. To enable direct analysis of frozen ice samples a special laser ablation chamber was constructed. Direct analysis reduces the risk of contamination. The defined removal of material from the ice surface by means of a laser beam leads to higher spatial resolution (300– 1000 μm) in comparison to investigations with molten ice samples. This is helpful for the detection of element signatures in annual layers of ice cores. The method was applied to the successful determination of traces for the elements Mg, Al, Fe, Zn, Cd, Pb, some rare-earth elements (REE) and minor constituents such as Ca and Na in ice cores. These selected elements serve as tracer elements for certain sources and their element signatures detected in polar ice cores can give hints to climate changes in the past. We report results from measurements of frozen ice samples, the achievable signal intensities, standard deviations and calibration graphs as well as the first signal progression of 208Pb in an 8,000-year-old ice core sample from Greenland. In addition, the first picture of a crater on an ice surface burnt by an IR laser made by cryogenic scanning electron microscopy is presented.
Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser by J. S. Becker; D. Tenzler (pp. 637-640).
The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9–1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1–10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.
A simple method of target preparation for the bulk analysis of powder samples by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) by W. Klemm; G. Bombach (pp. 641-646).
A simple and rapid procedure using a glue technique has been developed for the preparation of stable targets from powder samples for bulk analysis by LA– ICP–MS. The procedure was evaluated for the analysis of trace elements in SiC, of rare-earth elements in different types of silicate (rocks, sediments, and soils), and of Au and platinum-group elements in geological silicates. The test analysis was conducted using an IR laser in combination with a quadrupole mass spectrometer. The recommended preparation procedure offers the possibility of different types of calibration, for example application of certified reference samples in combination with prepared spiked samples on a base of a natural or synthetic matrix, or addition calibration. The resulting calibration functions are linear over a range of several decades. The trueness of the results was evaluated by use of certified reference samples. Analytical concentration ranges, detection limits, and the relative standard deviations are reported.
Progress in multi-ion counting spark-source mass spectrometry (MIC-SSMS) for the analysis of geological samples by K. P. Jochum; B. Stoll; J. A. Pfänder; M. Seufert; M. Flanz; P. Maissenbacher; M. Hofmann; A. W. Hofmann (pp. 647-653).
Spark source mass spectrometry (SSMS) has experienced important and significant improvements in nearly all analytical features by the use of a multiple ion counting (MIC) system. Two procedures have recently been developed to further increase the analytical capabilities of MIC-SSMS in geochemistry. These are a mathematical correction of interferences, which is often necessary for the ultra trace element analysis of Nb, Ta, Zr, Hf and Y, and the development of an autospark system to hold the total ion beam constant.New analytical data for geological samples, especially international reference materials, are presented using the improved MIC-SSMS technique. The data set consists of high precision and low abundance data for Zr, Nb and Y in depleted reference materials. The MIC-SSMS results are compared with those of conventional SSMS using photoplates for ion detection. The precision of the MIC-SSMS isotope ratio measurements (about 1%) is more than a factor of 3 better than that of conventional SSMS, as demonstrated by analyses of Hawaiian samples. Total uncertainties of MIC-SSMS concentration data including all sources of error are generally between 2 and 5% for concentrations higher than about 0.3 μg/g and about 10% for trace element abundances in the ng/g range.
Modeling of the sputtering process of cubic silver halide microcrystals and its relevance in depth profiling by secondary-ion mass spectrometry (SIMS) by J. Lenaerts; Geert Verlinden; Velislava A. Ignatova; L. Van Vaeck; Renaat Gijbels; Ingrid Geuens (pp. 654-662).
Secondary-ion mass spectrometry is frequently used for concentration–depth profiling of macroscopic samples, but it is certainly not a common analytical technique for the analysis of sub-micrometer-size particles. This is because of the additional ion-bombardment-induced artifacts which can occur when a three-dimensional microvolume is sputtered, instead of a flat surface.This paper presents a model of how small cubic photographic Ag(Cl,Br) crystals are eroded under primary-ion bombardment, and the extent to which secondary ions generated at different faces are extracted. The latter is studied by means of the program SIMION, which simulates ion trajectories in complex electrical field systems.It is shown that up to 90% of the secondary ions originating from the side face of a cubic crystal are unable to reach the detector, in contrast with most secondary ions originating from the top face. The angular dependence of the sputtering yield and the elemental ratio of Br/Cl sputtered particles have been calculated by using the well-known computer code TRIM (transport of ions in matter) under some limiting assumptions (possible preferential sputtering is disregarded and a steady-state sputtering process is assumed). The validity of the theoretical model and the calculated results were checked with experimental data. On the basis of the depth profiles presented it is explained why it is still possible to measure an interface inside a cubic volume, even though a group of several hundred crystals is sputtered simultaneously, and even though the orientations of the distinct faces of the cubes relative to the angle of incidence of the primary-ion beam are different.
Design and development of a new program for data processing of mass spectra acquired by means of a high-resolution double-focusing glow-discharge mass spectrometer by J. Robben; Davy Dufour; R. Gijbels (pp. 663-670).
An new program has been developed and implemented for data analysis of mass spectra obtained by use of the VG9000 glow-discharge mass spectrometer. The program, designed to run in a Windows 9X environment includes several tools for import and export of data, cluster generators, etc. An automated technique for the interpretation of mass spectra is also built into the program; this enables faster and operator-independent interpretation. When major interferences or not-well defined signals are involved, the automated technique might fail to find the correct result. Therefore, a manual, VG9000 software-like, bypass is at hand. A comparison of the different techniques and programs shows, in general, comparable results.An installable version of the software is available on the university FTP-server (ftp://PLASMA-FTP.uia.ac.be/ private/imsas/).