Minimising the Effects of Isobaric Product Ions in SIFT-MS Quantification of Acetaldehyde, Dimethyl Sulphide and Carbon Dioxide

David      Smith; Thomas   W.E.   Chippendale; Patrik      Spanel

Abstract

Analyses of the headspace of cell cultures using selected ion flow tube mass spectrometry, SIFT-MS, over the last few years have usually revealed the simultaneous presence of acetaldehyde, AA, and carbon dioxide, CO2. The characteristic primary product ions of reactions of the H3O+ ions with these compounds are at m/z 45, 63 and 81 for AA and m/z 63 for CO2. Recently, the presence of dimethyl sulphide, DMS, reaction of which with H3O+ ions also results in product ions at m/z 63 and 81, has also been detected in mammalian cell and bacterial cell culture headspace. The challenge now is to facilitate quantification of AA, DMS and CO2 when they coexist in humid air samples. Hence, an assessment has been made of the ion chemistry of H3O+ and NO+ with AA, DMS and CO2 in order to seek the appropriate procedures for their analyses by SIFT-MS. Thus, appropriate analytical reactions have been identified and kinetics library entries have been constructed for the analyses of these three compounds. Separate analysis of AA and carbon dioxide can now be achieved when they coexist in a humid sample by using both H3O+ and NO+ reagent ions in SIFT-MS, and the present study has revealed that DMS can be separately identified in a humid mixture using NO+ reagent ions. An additional experimental study has also shown how the CO2 concentration can be approximated using NO+ ions, which had not been considered in previous SIFT-MS analyses.

Keywords: Selected ion flow tube mass spectrometry, SIFT-MS, acetaldehyde, carbon dioxide, dimethyl sulphide.

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