Molybdenum isotope ratios

Molybdenum isotope ratio measurements by MC-ICP-MS (Plasma 54) have been carried out using Zr or Ru elemental spikes to study the mass discrimination during the whole analytical procedure including sample preparation.146 A laboratory fractionation of Mo isotopes of about 0.15 % is observed during ion exchange by offline Mo separation. Using this analytical technique, possible natural isotope variation of Mo can be determined with a precision of 0.02 %. 

Molybdenum Isotope Ratios and Global Ocean Paleoredox... 

Malinovsky, D., Rodushkin, L, Baxter, D., Ingri, J., and Ohlander, B. (2005) Molybdenum isotope ratio measurements on geological samples by MC-ICPMS. Int. J. Mass Spearom., 245, 94-107. 

This useful technique has made many contributions to radio- and nuclear chemistry, although primarily for investigational purposes rather than those of separation for its own ends. Thode and his co-workers have made many investigations into the inert gases produced in fission and it was by these means that the fine structure of fission was first discovered (79), (121). Since then several other elements, the rare-earths, strontium, caesium, zirconium, and molybdenum (35), (50), (132) have been investigated, and the isotopic ratios obtained provide relative values of fission-yields which are more accurate than can be obtained by standard radiochemical means. The latter technique, however, requires rather less heavily irradiated material than the former. 

Molybdenum isotope variations appear to be on the order of 3.5%o in Mo/ Mo ratios, where the largest fractionation is seen between aqueous Mo in seawater and that incorporated in Fe-Mn crusts and nodules on the seafloor (Chapter 12 Anbar 2004). This isotopic contrast is interpreted to reflect fractionation by Mo sorption to Mn oxide-rich sediments relative to aqueous Mo. The 5 Mo values for euxinic sediments in turn are distinct from those of Fe-Mn crusts, highlighting the isotopic contrasts between major repositories of Mo in surface and near-surface environments. As discussed by Anbar (2004) in Chapter 12, a major focus of research on Mo isotopes has been the potential use as a paleoredox indicator in marine systems. 

Taylor SR, McLennan SM (1985) The Continental Crust Its Composition and Evolution. Blackwell, Boston Tuit CB, Ravizza G (2003) The marine distribution of molybdenum. Geochim Cosmochim Acta 67 A4950 Tumlund JR, Keyes WR, Peiffer GL (1993) Isotope ratios of molybdenum determined by thermal ionization mass spectrometry for stable isotope studies of molybdenum metabolism in humans. Anal Chem 65 1717-1722... 

Figure 4.2 shows the SIMS spectrum of a promoted iron-antimony oxide catalyst used in selective oxidation reactions. Note the simultaneous occurrence of single ions (Si+, Fe+, Cu+, etc.) and molecular ions (SiO+, SiOH+, FeO+, SbO+, SbOSi+). Also clearly visible are the isotope patterns of copper (two isotopes at 63 and 65 amu), molybdenum (seven isotopes between 92 and 100 amu), and antimony (121 and 123 amu). Isotopic ratios play an important role in the identification of peaks, because all peak intensities must agree with natural abundances. Figure 4.2 also illustrates the differences in SIMS yields of the different elements although iron and antimony are present in comparable quantities in the catalyst, the iron intensity in the spectrum is about 25 times as high as that of antimony ... 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

Betti (1996) and co-workers used GD-MS for sample screening in isotopic measurements of zirconium, silicon, lithium, boron, uranium, and plutonium in nuclear samples. The results obtained from the GD-MS were compared with results from thermal ionization mass spectrometry (TIMS). For boron and lithium concentrations from //g/g to ng/g levels, isotopic ratios determined by GD-MS were comparable to TIMS in terms of accuracy and precision. Uranium isotopic ratios determined by GD-MS were also in good agreement with values measured by TIMS with regards to accuracy. Chartier et al. (1999) used GD-MS to analyze erbium and uranium in molybdenum-uranium fuel samples. The ratio of 166Er to 238U was then compared to numbers determined by thermal ionization mass spectrometry. The ratio of erbium to uranium was accurate to within 3% of the number determined by TIMS. 

For ultimate precision and accuracy, either MC-TIMS or MC-ICP-MS is required. Achievable precisions for MC-ICP-MS are of the order of 0.002-0.01% [299-302]. These techniques have been developed and applied exclusively to study natural isotope fractionation phenomena in geological samples. While double-spiking techniques are required for TIMS to differentiate between natural and instrumental fractionation [297], measurement bias has been corrected for in MC-ICP-MS measurements by normalization to the isotope ratios of a doped zirconium or ruthenium standard [301], a palladium standard ]302] or by standard sample bracketing using a molybdenum standard ]303]. 

Lu, Q. and Masuda, A. (1992) High accuracy measurement of isotope ratios of molybdenum in some terrestrial molybdenites. J. Am. Soc. Mass SpeUrom., 3, 10-17. 

In the latter, when equal amounts of deuterated and undeuterated 2,2 -divinylbiphenyls were combined with either molybdenum or tungsten catalysts, the ratios of undeuterated, dideuterated, and tetradeuterated molecules after about % reaction were found to be approximately 1 2 1 (24.3% isotope scrambling in the remaining divinylbiphenyls was measured as... 

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