Mass resolution from oxide ions

Figure 6.4 Mass resolution required for separation of atomic ions a) from oxide ions and b) from diatomic argon ions.

One of the challenges in measuring isotope ratios accurately is to achieve acceptable mass resolution to separate atomic ions from polyatomic ions, largely consisting of argide, hydride, and oxide ions. For example, in the measurement of Fe isotopes ( Fe, Fe, Fe, and Fe), common spectral interferences occur as a result of the presence of ArN+, ArO+, and ArOH ions at masses 54, 56, 57,... 

Diphenylthiirene 1-oxide and several thiirene 1,1-dioxides show very weak molecular ions by electron impact mass spectrometry, but the molecular ions are much more abundant in chemical ionization mass spectrometry (75JHC21). The major fragmentation pathway is loss of sulfur monoxide or sulfur dioxide to give the alkynic ion. High resolution mass measurements identified minor fragment ions from 2,3-diphenylthiirene 1-oxide at mje 105 and 121 as PhCO" and PhCS, which are probably derived via rearrangement of the thiirene sulfoxide to monothiobenzil (Scheme 2). 

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