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A new negative and positive gas ion source for isotope ratio mass spectrometry
Author(s) -
Pieńkos Tomasz,
Hałas Stanisław
Publication year - 2017
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7879
Subject(s) - chemistry , mass spectrometry , analytical chemistry (journal) , ion source , ion , electron ionization , isotope , ionization , chromatography , physics , organic chemistry , quantum mechanics
Rationale The goal of this research was to construct an effective gas ion source for isotope ratio mass spectrometry, which generates sufficiently strong and stable ion beams for multiple isotope ratio analysis of sulfur and oxygen from readily available gases such as SO 2 , CO 2 , CO, O 2 and chlorine from CH 3 Cl gas. Methods By means of a 60° sector mass spectrometer equipped with a new type of sensitive ion source and with a dual‐inlet system and triple collector assembly, we have measured 34 S/ 32 S and challenging 36 S/ 32 S isotope ratios using positive sulfur ions generated from SO 2 gas. The new ion source differs from the Nier‐type ones by the electron beam being replaced with a tungsten filament. The obtained isotope signals of 32 S + , 34 S + and 36 S + were from 1 to 5 V (depending on the pressure of admitted gas) on high‐ohm resistors of 200 MΩ, 5 GΩ and 500 GΩ, respectively. The variable 33 S peak was not recorded as useful due to interference from H 32 S + ions. Results Although the ionizing electrons in the new ion source have significant energy dispersion the obtained peak profiles are flat‐topped and they lead to good resolving power for the mass spectrometer (M/∆M ≈ 100). The achieved precision of δ 34 S and δ 36 S determination was better than ±0.01 and ±0.1‰, respectively. The determination of 37 Cl/ 35 Cl in a volatile organic compound CH 2 Cl 2 was easily achieved on Cl – negative ions with a precision of ±0.005‰. Conclusions The new ion source has great potential in the quantitative analysis of gases on positive ion mass spectra as well as, in the case of gases with high electron affinity such as CH 3 Cl, CH 3 Br, SF 6 , SiF 4 , on negative ones. It usefulness was demonstrated on an example of multiple sulfur isotope analysis and 37 Cl/ 35 Cl ratio determination with great precision. A negative ion source of this type will probably be useful in a more complicated instruments used in SIMS or AMS. Copyright © 2017 John Wiley & Sons, Ltd.