Importance of Gas Temperature

Until recentiy, FAIMS was operated at a fixed gas temperature-room T, or, less often, somewhat elevated temperature to improve ion desolvation or prevent vapor condensation in the analyzer. For example, the study of orgP compounds used air at 60 °C. 

The dependence of Ec/N versus E /N plots on T might reflect the inelasticity of rotational or vibrational scattering (2.5 and 2.6) increasing at higher T. However, 

FIGURE 3.32 Schematic KiEpp/N) curves for cases where heating the gas from Ti (short dash) to T2 (long dash) does not (a) and does (h) substantially affect AAT between some Ei and 2 measured in FAIMS. Equal values of AT = 2 — Ti appear different at Ei and 2 because Tef by Equation 1.26 depends on E/N nonlinearly. 

Besides its influence on the separation parameters of specific ions, the gas temperature may also affect the nature of present species through thermal dissociation or isomerization. The gas Tin DT IMS was varied to identify the ions more specifically, for example via characterization of the products of isomerization or the measurement of associated thermodynamic and kinetic data. Such phenomena were observed in FAIMS and may be similarly useful, though here one must account for the field heating that elevates the ion internal T above the gas T (3.5). 

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