Multiple-collector Mass Spectrometry Research Articles

Natural isotopic variation of heavy elements by multiple-collector mass spectrometry

Natural isotopic variation of heavy elements by multiple-collector mass spectrometry

Determination of the selenium isotopic compositions in Se-rich yeast by hydride generation-inductively coupled plasma multicollector mass spectrometry

A method was developed for the precise determination of selenium isotopic compositions (δ82/77Se, δ82/76Se and δ82/74Se) by hydride generation inductively coupled plasma multiple collector mass spectrometry (HG-MC ICP MS) in Se-rich yeast. The conversion of all the selenium forms into Se(IV) during digestion and reduction steps was investigated by anion-exchange ICP quadrupole MS (SAX ICP Q MS) and was found to be complete. Measurement precision values expressed as deltas (δ) with regard to NIST SRM3149 were between 0.2–0.4‰ (2SD) over a period of 6 months for 25 or 50 ng mL−1 of introduced selenium. The application of the method to the analysis of nine Se-rich yeast supplements from different manufactures showed significant variations in the isotope ratios suggesting that the latter can be an attractive parameter for the yeast provenance discrimination.

The development of multiple collector mass spectrometry for isotope ratio measurements

Multiple collector mass spectrometry has enabled significant advances in our understanding of geological, biological, nuclear, and physical processes in terrestrial and extra-terrestrial environments. The development of improved mass spectrometers and more efficient and universal ionization techniques is driven by the requirement to extract the highest quality information from the smallest amount of sample possible. Important milestones include the refinement of the variable multiple collector system, improvements in current amplifier technology to achieve ultimate precision and accuracy, increased abundance sensitivity, tailored ion optics using zoom optics and increased ion optical magnification to meet the special requirements of multiple collection, increased signal-to-noise using multiple ion counting devices, and the integration of a high efficiency ionization inductively coupled plasma source. New applications are on the horizon in many fields in addition to the geological and cosmological origins of high precision isotope ratio mass spectrometry. This is made possible by in situ sampling of samples at high spatial resolution using laser ablation techniques as well as online coupling of chromatographic devices to study elemental isotope effects in isolated molecular species. This paper describes and discusses the instrumental development of multiple collector isotope ratio technology and highlights some emerging applications.

Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes

We present the first detailed Pb, Nd, Sr and Hf isotopic study of a classic HIMU system. The Hf isotopic compositions of 18 representative basaltic lavas from the length of the Cameroon volcanic line have been determined using the new technique of inductively coupled plasma magnetic sector multiple collector mass spectrometry. The Hf isotopic compositions are found to be the same on average in continental, oceanic, and continental-oceanic boundary sectors. The three islands from the oceanic sector, Pagalu, São Tomé and Principe, display a large spread in Pb and Sr isotopic compositions but have Hf and Nd isotopic compositions that are both uniform and identical to the HIMU islands of Tubuai and St. Helena. The Hf and Nd isotopic compositions of HIMU centers appear to be a more reproducible and characteristic feature than Pb and Sr isotopic compositions. On this basis, basalts along the entire Cameroon line have a similar origin. The data imply that Pagalu, with its unradiogenic 206Pb/ 204Pb (∼ I9) has incorporated the same Hf and Nd as Principe, Bioko, Etinde, Mt. Cameroon, St. Helena and Tubuai, all with average 206Pb/ 204Pb > 20. These data are consistent with the conclusion that the increase in 206Pb/ 204Pb toward the COB is due to young fractionation in U/Pb within the upper mantle. Neither the Hf isotopic composition of Cameroon line basalts, nor that of HIMU basalts in general, can be explained by recycling and storage of subducted N-MORB. Storage of more enriched components is required. Furthermore, the uniformity in HfNd isotopic space is difficult to explain by any recycling models and is more consistent with the HIMU source representing a distinctive and potentially important reservoir with specific Lu/Hf, Sm/Nd and age.

Precise Measurement of Isotope Ratios with a Double-Focusing Magnetic Sector ICP Mass Spectrometer

The potential of a commercially available double-focusing magnetic sector ICP mass spectrometer (Element, Finnigan MAT, Bremen, Germany) for precise isotope ratio measurement at the low-resolution setting (R = 300) was evaluated. Optimization of scanning conditions led to a relative standard deviation for a set of 10 consecutive 2 min measurements of ∼0.1% ((206)Pb(+)/(207)Pb(+)) at signal intensities of ∼200 000 counts/s (peak height). This compares favorably with the best values ever reported for quadrupole ICPMS and barely exceeds the theoretical value (counting statistics). Increasing the signal intensity to values ≥500 000 counts/s (peak height) resulted in a further reduction of the RSDs obtained (for both (25)Mg(+)/(26)Mg(+) and (206)Pb(+)/(207)Pb(+)) to typically 0.04%. These figures are remarkably better than those reported for commercially available quadrupole ICPMS systems. This improvement significantly reduces the difference between isotope ratio precision of ICPMS on one hand and those of thermal ionization mass spectrometry and plasma source multiple collector mass spectrometry on the other.

Precise determinations of the isotopic compositions and atomic weights of molybdenum, tellurium, tin and tungsten using ICP magnetic sector multiple collector mass spectrometry

Precise determinations of the isotopic compositions of molybdenum, tellurium, tin and tungsten were obtained utilizing an inductively coupled plasma (ICP) source magnetic sector mass spectrometer equipped with multiple collectors. The results of this study are comparable to those measured by conventional and negative thermal ionization mass spectrometry (TIMS and NTIMS) and the values recommended by the International Union of Pure and Applied Chemistry (IUPAC), but with improvement in precision by up to two orders of magnitude. The relative isotopic abundances and atomic weight for each element calculated from the data obtained in this study are also in excellent agreement with previously published values. The only disagreement between this study and IUPAC recommended values is for tellurium. However, with the exception of 130Te, the Te data are in good agreement with those reported in a recent study by De Laeter [1]. The results of this study demonstrate the capability of this new instrument to produce precise and reproducible isotopic data for elements that are difficult to ionize and measure with TIMS. Furthermore, the greater precision of isotopic measurements possible with the ICP source multiple collector magnet sector mass spectrometer greatly enhances the prospects for research on the distribution and isotopic compositions of these elements in terrestrial and meteoritic materials.

Recent developments in inductively coupled plasma magnetic sector multiple collector mass spectrometry

This paper describes advances in isotopic measurements that have been made with an inductively coupled plasma source magnetic sector multiple collector mass spectrometer and presents results of new experiments aimed at further evaluating the instrument's capability. It is shown using standard solutions that trace element ratios such as Rb/Sr can be measured precisely without isotope dilution by comparison with reference solutions of known composition. Similarly, using a new wide flight tube, Pb isotopic compositions and U/Pb ratios can be accurately measured simultaneously without isotope dilution. The effects of deliberately including changes in the running conditions (r.f. power) are shown to be significant for measuring trace element ratios but not for mass bias and interference-corrected isotopic compositions. Finally, it is demonstrated that precise and accurate isotopic compositions of elements as refractory as W can be determined relatively easily by solution nebulization and even by direct laser ablation of complex silicates. Spectral interferences in such experiments are negligible. These experiments serve to highlight the remarkable potential that this new field offers for hitherto difficult isotopic measurements in nuclear, earth, environmental and medical sciences. Isotopic measurements can be made that are reproducible at high precision through a range of running conditions, even in the presence of isobaric interferences. The ability to correct for mass discrimination accurately using a second element of similar mass, the very high sensitivity for elements that are otherwise difficult to ionize, the demonstrated capability for laser ablation work and the ability to measure through a wide mass range simultaneously give this instrument major advantages over other more traditional techniques of isotopic measurement.

In situ hafnium isotope ratio analysis of zircon by inductively coupled plasma multiple collector mass spectrometry

Hf isotopic data are reported for ten ∼0.01-mm 2 subareas of a zircon crystal separated from the ∼ 318-Ma diatreme of Elie Ness, Fife, Scotland. In situ analysis was achieved by ablation sampling with a Nd:YAG laser into an inductively-coupled plasma, with ions dispersed by a sector magnet and integrated in a 7-Faraday multicollector array. Despite large interferences from Yb (16% of mass 176) and Lu (0.4% of mass 176), 2 se precision of ± 0.00004–0.00014 was achieved on 176Hf/ 177Hf in each subarea, each representing the analysis of ∼10 ng of Hf. Overall reproducibility of ± 0.00005 (2 sd) was obtained between the ten subareas, only a factor of 2–3 worse than that achieved by conventional TIMS Hf analysis based on 1–3 μg HE Reproducibility of single-spot analyses is about a factor of 2 better than reported for ion microprobe studies of zircon Hf, with far less potential for inaccuracies caused by molecular isobaric interferences. The Elie Ness zircons are isotopically homogeneous in Hf, but the technique is expected to have great value for the understanding of multicomponent zircons from granitoids and sediments.

High-Precision Lead Isotope Ratio Measurement by Inductively Coupled Plasma Multiple Collector Mass Spectrometry

An inductively coupled plasma (ICP) ion source coupled to a magnetic sector mass analyser equipped with seven Faraday detectors has been used to measure the lead isotope ratios in solutions of Sanshiro Pond sediment collected at the University of Tokyo, airborne particulates collected at Shinjuku in Tokyo and Merck multielement standard product number 97279494. A thallium correction technique was utilised to allow a simultaneous correction for mass bias. This work followed an earlier interlaboratory comparison study of the above-mentioned solutions using ICP quadrupole mass spectrometry, and has demonstrated a considerable improvement in analytical precision. The following isotope ratio measurements were recorded. Pond sediment solution containing 82ng ml-1 lead: 206Pb/204Pb=17.762±0.014; 206Pb/ 207Pb=1.1424±0.0009; 208Pb/204Pb=37.678±0.034. Airborne particulate solution containing 45 ng ml-1 lead: 206Pb/ 204Pb=17.969±0.006; 206Pb/207Pb=1.1528±0.0003; 208Pb/204Pb=37.915±0.021. Merck multielement standard solution containing 100ng ml-1 lead: 206Pb/204Pb=19.255±0.015; 206Pb/207Pb=1.2238±0.0004; 208Pb/204Pb=38.476±0.021 (All errors are given as ±2 standard deviations).

Communication. Isotope ratio measurement by inductively coupled plasma multiple collector mass spectrometry incorporating a high efficiency nebulization system

Isotope ratio analysis by inductively coupled plasma multiple collector mass spectrometry has been performed utilizing a high efficiency desolvating nebulization system for sample introduction. The high accuracy and high precision analysis of uranium, lead and hafnium reference materials at a concentration of 50 ng ml–1 are reported. Use of the high efficiency device has increased sample transmission and hence increased ion-signal levels by a factor of ten compared with conventional nebulization. The analysis of each uranium and lead solution required 29 ng of sample while the analysis of each hafnium solution required 290 ng of sample. The accuracy and precision of the measurements are comparable with those obtained by thermal ionization mass spectrometry. Transmission calculations indicate an ion:atom ratio of 1:5500 for each of the three elements. This is superior to that observed with other plasma source mass spectrometers and in the case of hafnium, exceeds that achieved with thermal ionization mass spectrometers.