title: A new negative and positive gas ion source for isotope ratio mass spectrometry.
abstract: BACKGROUND
  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 SO2, CO2, CO, O2and chlorine from CH3Cl 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 measured34S/32S and challenging36S/32S isotope ratios using positive sulfur ions generated from SO2gas. The new ion source differs from the Nier-type ones by the electron beam being replaced with a tungsten filament. The obtained isotope signals of32S+,34S+and36S+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 variable33S peak was not recorded as useful due to interference from H32S+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 δ34S and δ36S determination was better than ±0.01 and ±0.1‰, respectively. The determination of37Cl/35Cl in a volatile organic compound CH2Cl2was 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 CH3Cl, CH3Br, SF6, SiF4, on negative ones. It usefulness was demonstrated on an example of multiple sulfur isotope analysis and37Cl/35Cl 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.
authors.affiliation: Mass Spectrometry Laboratory, UMCS Lublin, Pl. M. Curie-Skłodowskiej 1, 20-031, Lublin, Poland.
authors.forename: Tomasz
authors.identifier: http://orcid.org/0000-0003-1300-3721
authors.initials: T
authors.lastname: Pieńkos
authors.affiliation: Mass Spectrometry Laboratory, UMCS Lublin, Pl. M. Curie-Skłodowskiej 1, 20-031, Lublin, Poland.
authors.forename: Stanisław
authors.identifier: http://orcid.org/0000-0002-0190-4314
authors.initials: S
authors.lastname: Hałas