How to Use Ion-Molecule Reaction Data Previously Obtained in Helium at 300 K in the New Generation of Selected Ion Flow Tube Mass Spectrometry Instruments Operating in Nitrogen at 393 K

Selected ion flowtube mass spectrometry (SIFT-MS) instrumentshave significantly developed since this technique was introduced morethan 20 years ago. Most studies of the ion-molecule reactionkinetics that are essential for accurate analyses of trace gases andvapors in air and breath were conducted in He carrier gas at 300 K,while the new SIFT-MS instruments (optimized to quantify concentrationsdown to parts per trillion by volume) operate with N-2 carriergas at 393 K. Thus, we pose the question of how to reuse the datafrom the extensive body of previous literature using He at room temperaturein the new instruments operating with N-2 carrier gas atelevated temperatures. Experimentally, we found the product ions tobe qualitatively similar, although there were differences in the branchingratios, and some reaction rate coefficients were lower in the heatedN(2) carrier gas. The differences in the reaction kineticsmay be attributed to temperature, an electric field in the currentflow tubes, and the change from He to N-2 carrier gas. Theseresults highlight the importance of adopting an updated reaction kineticslibrary that accounts for the new instruments' specific conditions.In conclusion, almost all previous rate coefficients may be used afteradjustment for higher temperatures, while some product ion branchingratios need to be updated.