Measuring amount ratios of gas isotopes by two primary methods

Abstract

Procedures developed for accurate measurement of amount of substance ratios for gas isotopes, as used to improve our knowledge of the Avogadro constant and checked for quantitative conformity against kinetic gas theory, were used to measure synthetic mixtures of enriched xenon gas isotopes, prepared by (micro)-gravimetry as is usual in the preparation of synthetic gas compound mixtures. This allowed a totally independent evaluation, on the same samples, of the relative combined standard uncertainty of (a) the procedure to perform direct measurements of amount of substance ratios of gas isotopes in the redetermination of the Avogadro constant and (b) the gravimetric preparation procedure. The results of both procedures, mass spectrometry and gravimetry, agree to a relative uncertainty of 2 × 10-3 for amount measurements of the major abundant isotopes. Thus it seems that a direct measurement of isotopic gas mixtures (e.g. of natural isotopic composition) is now possible for xenon isotopes- and probably also for other gaseous isotopes- without necessarily having to rely on ''calibration'' by means of values provided by measurements of gravimetrically prepared isotope mixtures. However, synthetic mixtures may be needed for validation and verification purposes, in particular for quality assurance (QA).

Estimating the Triple-Point Isotope Effect and the Corresponding Uncertainties for Cryogenic Fixed Points

“…The mass fractionation line is calculated with respect to the Xe isotope reference gas IRMM-2000 [25] on which the currently recommended molar mass [3] is based. The other data are taken from the literature: Nier 1950 [26]; IRMM, 1994 [27]; IRMM L'Air Liquide 1998 [28]; Podosek et al 1971 [29]; Basford et al 1973 [30]; Nief NBS-104 and Dibeler NBS-104 [31]; Khynhov, 1989, as cited in [16], and Hill and Steele [16] cannot be ruled out. Assuming that this apparent isotopic variability is real, and a sensitivity of 0.75 mK·mol·g −1 derived above, this corresponds to variability in the Xe TP of only 21 µK.…”

Reformulated 17O correction of mass spectrometric stable isotope measurements in carbon dioxide and a critical appraisal of historic ‘absolute’ carbon and oxygen isotope ratios

“…Calibrated (or 'absolute') isotope ratio measurements are cumbersome because they require either special mass spectrometers or careful calibration using synthetic mixtures of essentially pure isotopes (Aregbe et al, 1998). Assonov and Brenninkmeijer (2003b) avoided performing such calibrated isotope ratio measurements, using a similar approach as previous authors (Santrock et al, 1985;Li et al, 1988a): They redetermined the 17 O/ 16 O isotope ratio of VPDB-CO 2 ''on the scale of" its 13 C/ 12 C isotope ratio.…”

[{Au(IPr)}2(μ‐OH)]X Complexes: Synthetic, Structural and Catalytic Studies

“…Some of these difficulties have been overcome by the use of the ‘isotope dilution curve’ method,5 which uses two reference blends prepared by diluting a pure sample of the same substance as the unknown with the highly enriched spike. However, published applications of IDMS to gas analysis6–8 have made use of mass spectrometers using dual‐inlets to provide very precisely controlled conditions for the input of the analytes to the analyser. The method would find wider application if it could be used with a gas chromatograph at the input to separate the analyte from the matrix prior to the mass spectrometric analysis 9,10.…”