Estimation of Mass Discrimination Factor for a Wide Range of m/z by Argon Artificial Isotope Mixtures and NF₃Gas

Abstract

Absolute isotope ratio is a critical constituent in determination of atomic weight. To measure the absolute isotope ratio using a mass spectrometer, mass discrimination factor, f MD , is needed to convert measured isotope ratio to real isotope ratio of gas molecules. If the f MD could be predicted, absolute isotope ratio of a chemical species would be measureable in absence of its enriched isotope pure materials or isotope references. This work employed gravimetrically prepared isotope mixtures of argon (Ar) to obtain f MD at m/z of 40 in the magnetic sector type gas mass spectrometer (gas/MS). Besides, we compare the nitrogen isotope ratio of nitrogen trifluoride (NF 3 ) with that of nitrogen molecule (N 2 ) decomposed from the same NF 3 thermally in order to identify the difference of f MD values in extensive m/z region from 28 to 71. Our result shows that f MD at m/z 40 was −0.044 % ± 0.017 % (k = 1) from measurement of Ar artificial isotope mixtures. The f MD difference in the range of m/z from 28 to 71 is observed −0.12 % ± 0.14 % from NF 3 and N 2 . From combination of this work and reported f MD values by another team, IRMM, if f MD of −0.16 % ± 0.14 % is applied to isotope ratio measurement from N 2 to SF 6 , we can determine absolute isotope ratio within relative uncertainty of 0.2 %.

Triple-Point Temperature and the Isotopic Composition of Three Commercial Neon Gases

“…A detailed description of the mass spectrometer and the measurement procedure for argon and NF 3 isotopes are described in the literature [17,18]. The principle and procedure of the operation of the mass spectrometer for neon are similar, and we briefly explain the specific matters related to neon isotope measurements.…”

New Analytical Method for Measuring the Atomic Weight of Neon Using Gas Chromatography with a Thermal Conductivity Detector

“…For validation of the neon atomic weights obtained by GC-TCD, each isotopeamount fraction of the neon samples was measured using a gas/MS (Finnigan MAT 271). The experimental procedure is the same method reported by Lee et al 23 and Min et al, 30 and the details and principles of MAT 271 are also described in the same references. For each sample, the isotope-amount fractions of neon for 21 x and 22 x were expressed as ratios for 20 x, as R( 21 x/ 20 x) and R( 22 x/ 20 x), respectively.…”

“…The ratio of the neon isotope reference gas used in this study was 22 x/ 20 x = 0.032987(10), which was gravimetrically prepared by using 99.96% 20 Ne (Isotech, USA) and 99.9% 22 Ne (Iceblick, Romania). The gravimetric preparation procedure of the neon isotope reference gas was described by Min et al 30 and Yang et al 16 The f MD used in this experiment was −0.11%, and each atomic weight of the neon samples was corrected to this value. In addition, the background correction of Ar ++ and CO 2 ++ was performed, and it was negligible.…”