J. S. Becker

State-of-the-art and progress in precise and accurate isotope ratio measurements by ICP-MS and LA-ICP-MS{

The capability to determine isotope abundances is a main feature of mass spectrometry. The precise and accurate determination of isotope ratios is required for different application fields, such as: isotope ratio measurements of stable isotopes in nature, especially for the investigation of isotope variation in nature or age dating; determining isotope ratios of radiogenic elements in the nuclear industry; quality assurance of fuel material for reprocessing plants, nuclear material accounting and radioactive waste control; and tracer experiments using highly enriched stable isotopes or long-lived radionuclides in biological or medical studies. Inductively coupled plasma mass spectrometry and laser ablation ICP-MS (LA-ICP-MS) provides excellent sensitivity, precision and good accuracy for isotope ratio measurements with practically no restriction with respect to the ionization potential of the element investigated. Therefore both ICP-MS and LA-ICP-MS are increasingly replacing thermal ionization mass spectrometry (TIMS), which has been used as the dominant analytical technique for precise isotope ratio measurements for many decades. In the last few years instrumental progress for improving figures of merit in isotope ratio measurements in ICP-MS and LA-ICP-MS with a single ion detector has been achieved by the introduction of the collision cell interface, in order to dissociate disturbing argon-based molecular ions, to reduce the kinetic energy of ions and neutralize the disturbing argon ions of the plasma gas (Ar+). The application of the collision cell in ICP-MS results in higher ion transmission, improved sensitivity and better precision of isotope ratio measurements compared to ICP-MS without the collision cell. The most important instrumental improvement for isotope analysis by sector field ICP-MS was the application of a multiple ion collector device (MC-ICP-MS) (developed about 10 years ago) in order to obtain better precision of isotope ratio measurements of up to 0.002%, RSD.

Applications of inductively coupled plasma mass spectrometry and laser ablation inductively coupled plasma mass spectrometry in materials science

Abstract Inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) have been applied as the most important inorganic mass spectrometric techniques having multielemental capability for the characterization of solid samples in materials science. ICP-MS is used for the sensitive determination of trace and ultratrace elements in digested solutions of solid samples or of process chemicals (ultrapure water, acids and organic solutions) for the semiconductor industry with detection limits down to sub-picogram per liter levels. Whereas ICP-MS on solid samples (e.g. high-purity ceramics) sometimes requires time-consuming sample preparation for its application in materials science, and the risk of contamination is a serious drawback, a fast, direct determination of trace elements in solid materials without any sample preparation by LA-ICP-MS is possible. The detection limits for the direct analysis of solid samples by LA-ICP-MS have been determined for many elements down to the nanogram per gram range. A deterioration of detection limits was observed for elements where interferences with polyatomic ions occur. The inherent interference problem can often be solved by applying a double-focusing sector field mass spectrometer at higher mass resolution or by collision-induced reactions of polyatomic ions with a collision gas using an ICP-MS fitted with collision cell. The main problem of LA-ICP-MS is quantification if no suitable standard reference materials with a similar matrix composition are available. The calibration problem in LA-ICP-MS can be solved using on-line solution-based calibration, and different procedures, such as external calibration and standard addition, have been discussed with respect to their application in materials science. The application of isotope dilution in solution-based calibration for trace metal determination in small amounts of noble metals has been developed as a new calibration strategy. This review discusses new analytical developments and possible applications of ICP-MS and LA-ICP-MS for the quantitative determination of trace elements and in surface analysis for materials science.

Inorganic trace analysis by mass spectrometry

Mass spectrometric methods for the trace analysis of inorganic materials with their ability to provide a very sensitive multielemental analysis have been established for the determination of trace and ultratrace elements in high-purity materials (metals, semiconductors and insulators), in different technical samples (e.g. alloys, pure chemicals, ceramics, thin films, ionimplanted semiconductors), in environmental samples (waters, soils, biological and medical materials) and geological samples. Whereas such techniques as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS) have multielemental capability, other methods such as thermal ionization mass spectrometry (TIMS), accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS) have been used for sensitive mono- or oligoelemental ultratrace analysis (and precise determination of isotopic ratios) in solid samples. The limits of detection for chemical elements using these mass spectrometric techniques are in the low ng g -1 concentration range. The quantification of the analytical results of mass spectrometric methods is sometimes difficult due to a lack of matrix-fitted multielement standard reference materials (SRMs) for many solid samples. Therefore, owing to the simple quantification procedure of the aqueous solution, inductively coupled plasma mass spectrometry (ICP-MS) is being increasingly used for the characterization of solid samples after sample dissolution. ICP-MS is often combined with special sample introduction equipment (e.g. flow injection, hydride generation, high performance liquid chromatography (HPLC) or electrothermal vaporization) or an off-line matrix separation and enrichment of trace impurities (especially for characterization of high-purity materials and environmental samples) is used in order to improve the detection limits of trace elements. Furthermore, the determination of chemical elements in the trace and ultratrace concentration range is often difficult and can be disturbed through mass interferences of analyte ions by molecular ions at the same nominal mass. By applying double-focusing sector field mass spectrometry at the required mass resolution—by the mass spectrometric separation of molecular ions from the analyte ions—it is often possible to overcome these interference problems. Commercial instrumental equipment, the capability (detection limits, accuracy, precision) and the analytical application fields of mass spectrometric methods for the determination of trace and ultratrace elements and for surface analysis are discussed. q 1998 Elsevier Science B.V. All rights reserved

Ultratrace and Isotope Analysis of Long-Lived Radionuclides by Inductively Coupled Plasma Quadrupole Mass Spectrometry Using a Direct Injection High Efficiency Nebulizer

The direct injection high efficiency nebulizer (DIHEN) was explored for the ultrasensitive determination of long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U, (239)Pu, and (241)Am) and for precise isotope analysis by inductively coupled plasma mass spectrometry (ICPMS). The DIHEN was used at low solution uptake rates (1-100 μL/min) without a spray chamber. Optimal sensitivity (e.g., (238)U, 230 MHz/ppm; (230)Th, 190 MHz/ppm; and (239)Pu, 184 MHz/ppm) was achieved at low nebulizer gas flow rates (0.16 L/min), high rf power (1450 W), and low solution uptake rates (100 μL/min). The optimum parameters varied slightly for the two DIHENs tested. The detection limits of long-lived radionuclides in aqueous solutions varied from 0.012 to 0.11 ng/L. The sensitivity of the DIHEN was improved by a factor of 3 to 5 compared with that of a microconcentric nebulizer (MicroMist used with a minicyclonic spray chamber at a solution uptake rate of 85 μL/min) and a factor of 1.5 to 4 compared with that of a conventional nebulizer (cross-flow used with a Scott type spray chamber at a solution uptake rate of 1 mL/min). The precision of the DIHEN ranged from 0.5 to 1.7% RSD (N = 3) for all measurements at the 10 ng/L concentration level (∼3 pg sample size). The sensitivity decreased to 10 MHz/ppm at a solution uptake rate of 1 μL/min. The precision was about 5% RSD at a sample size of 30 fg for each long-lived radionuclide by the DIHEN-ICPMS method. The oxide to atom ratios were less than 0.05 (except ThO(+)/Th(+) ) and decreased under the optimum conditions in the following sequence: ThO(+)/Th(+) > UO(+)/U(+) > NpO(+)/Np(+) > PuO(+)/Pu(+) > AmO(+)/Am(+) > RaO(+)/Ra(+). Atomic and oxide ions were used as analyte ions for ultratrace and isotope analyses of long-lived radionuclides in environmental and radioactive waste samples. The analytical methods developed were applied to the determination of long-lived radionuclides and isotope ratio measurements in different radioactive waste and environmental samples using the DIHEN in combination with quadrupole ICPMS. For instance, the (240)Pu/(239)Pu isotope ratio was measured in a radioactive waste sample at a plutonium concentration of 12 ng/L. This demonstrates a main advantage of DIHEN-ICPMS compared with α-spectrometry, which cannot be used to selectively determine (239)Pu and (240)Pu because of similar α energies (5.244 and 5.255 MeV, respectively).

Laser ablation inductively coupled plasma mass spectrometry for the trace, ultratrace and isotope analysis of long-lived radionuclides in solid samples

Abstract The capability of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for determination of long-lived radionuclides in different materials (e.g., in geological samples, high-purity graphite and nonconducting concrete matrix) was investigated. The main problem in the quantification of the analytical results of long-lived radionuclides is that (except for geological samples) no suitable standard reference materials are available. Therefore, synthetic laboratory standards (graphite and concrete matrix doped with long-lived radionuclides, such as 99Tc, 232Th, 233U, 235U, 237Np, 238U) were prepared and used for quantification purposes in LA-ICP-MS. Different calibration procedures—the correction of analytical results with experimentally determined relative sensitivity coefficients (RSCs), the use of calibration curves and solution calibration by coupling LA-ICP-MS with an ultrasonic nebulizer—were applied for the determination of long-lived radionuclides, especially for Th and U in different solid samples. The limits of detection of long-lived radionuclides investigated in concrete matrix are determined in the pg g−1 range (e.g., for 237Np-50 pg g−1 in quadrupole LA-ICP-MS; for 233U-1.3 pg g−1 in double-focusing sector field LA-ICP-MS). Results of isotope ratio measurements of Th and U in synthetic laboratory standards and different solid radioactive waste materials of direct analysis on solid samples using LA-ICP-MS are comparable to measurements using the double-focusing sector field ICP-MS after separation of the analyte, even if no possible interference of atomic ions of analyte and molecular ions are expected. Furthermore, LA-ICP-MS allows precise and accurate isotope ratio measurements of Th and U in solid samples. For example, the isotope ratio 234U/238U = 0.000067 in radioactive reactor graphite was determined with a precision of 1.1% relative standard deviation (RSD).

Combination of PAGE and LA-ICP-MS as an analytical workflow in metallomics: state of the art, new quantification strategies, advantages and limitations

Metallomics (more specifically, metalloproteomics) is an emerging field that encompasses the role, uptake, transport and storage of trace metals, which are essential to preserve the functions of proteins within a biological system. The current strategies for metal-binding and metalloprotein analysis based on the combination of polyacrylamide gel electrophoresis (PAGE) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are discussed in this review. The advantages, limitations and the most recently developed and applied quantification approaches for this methodology are also described.

Ultratrace and precise isotope analysis by double-focusing sector field inductively coupled plasma mass spectrometry

Double-focusing sector field inductively coupled plasma source mass spectrometry with its capability of providing a very sensitive multi-element analysis has been established for the determination of trace and ultratrace elements in high-purity materials, environmental samples and radioactive waste materials. Some applications of double-focusing sector field ICP-MS for the multi-element analysis of trace and ultratrace impurities in high-purity inorganic materials are described. A matrix separation procedure for ZrO2 by liquid–liquid extraction after microwave-induced dissolution in an acid mixture is proposed in order to determine ultratrace impurities. The detection limits of ICP-MS reached after matrix separation in solid samples are in the low ng g–1 concentration range. The detection limits in ICP-MS (determined by the blank values of the chemicals used) are comparable to those of solid-state mass spectrometry, which allows the direct determination of trace impurities in high-purity solids. Isotope ratio measurements of Mg, K and Ca were performed to investigate the transport phenomena of nutrient solutions in plants by tracer experiments using highly enriched 25Mg, 26Mg, 41K, 42Ca and 44Ca isotopes. In order to separate the 38ArH+ and 40ArH+ ions from the 39K+ and 41K+analyte ions for potassium isotope ratio measurements, double-focusing sector field ICP-MS with an ultrasonic nebulizer was used at a mass resolution of 9000. The precision of potassium isotope ratio measurements was 0.7% (at a potassium concentration of 100 µg l–1). Isotope ratios of Mg and Ca (each at a concentration of 50 µg l–1) were determined at a mass resolution of 3000 with a precision of 0.4 and 0.5% on real biological samples. The accuracy of isotope ratio measurements of K and Mg was determined using isotopic standard reference materials with natural isotope composition (NBS SRM 985 and 980). The results of isotope ratio measurements of K, Mg and Ca on real biological samples doped with enriched stable isotopes are discussed.

Determination of long-lived radionuclides in concrete matrix by laser ablation inductively coupled plasma mass spectrometry☆

Abstract A laser ablation system using a Nd:YAG laser was coupled both to a quadrupole inductively coupled plasma (ICP) mass spectrometer and to a double-focusing sector field ICP mass spectrometer. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the determination of long-lived radionuclides in a concrete matrix. The investigated samples were two laboratory standards with a concrete matrix, which we doped with different long-lived radionuclides (e.g. 99 Tc, 232 Th, 233 U, 237 Np) from the ng g −1 to μ g −1 concentration range and an undoped concrete material (blank). Detection limits for long-lived radionuclides in the 10 ng g −1 range are reached for LA-ICP-MS using the quadrupole mass spectrometer. With double-focusing sector field ICP-MS, the limits of detection are in general one order of magnitude lower and reach the sub ng g −1 range for 233 U and 237 Np. A comparison of mass spectrometric results with those of neutron activation analysis on undoped concrete sample indicates that a semiquantitative determination of the concentrations of the minor and trace elements in the concrete matrix is possible with LA-ICP-MS without using a standard reference material.

Laser ionization mass spectrometry in inorganic trace analysis

SummaryAmong the different spectrometric techniques for trace analysis Laser Ionization Mass Spectrometry (LIMS) is well established as a trace analytical method. With the LIMS technique the sample material is evaporated and ionized by means of a focused pulsed laser in a laser microplasma, which is formed in the spot area of the irradiated sample. All chemical elements in the sample materials are evaporated and ionized in the laser plasma. The ions formed are separated according to their mass and energy by a time-of-flight, quadrupole or double focusing mass spectrometer. In this review the characteristics and analytical features, some recent developments and applications of laser ionization mass spectrometry in inorganic trace analysis are described.

Reduction of molecular ion interferences with hexapole collision cell in direct injection nebulization–inductively coupled plasma mass spectrometry

A hexapole collision cell was investigated for significant reductions of interferences by molecular ions in inductively coupled plasma mass spectrometry (ICPMS) using a direct injection high efficiency nebulizer (DIHEN). Collision induced reactions with hydrogen reduced isobaric interferences while the addition of helium as a collision gas enhanced analyte ion transmission through collisional focusing. Improved figures of merit were obtained for elements (Ca, Fe, Cr, As, Se) that are typically difficult to analyze with conventional quadrupole instruments. Sensitivities achieved with the DIHEN were higher (by factors ranging from 2 to 9) than those observed with a micronebulizer-spray chamber arrangement. Precision and detection limits were similar to or slightly improved over values obtained using the micronebulizer-spray chamber arrangement. The technique was successfully applied to the determination of Fe, Cr, Co, Cu, Pb, Al, Mn, Zn, Ag, and Sr on silicon wafer surfaces at a concentration range of (0.49–6.5) × 109 atoms cm−2, sampled by a 100 µL drop of H2O–H2O2–HF, as well as for the determination of Cr in DNA.