Direct Characterization of Heat-Induced Processes in FAIMS Using Spectral Normalization

3 Direct Characterization of Heat-Induced Processes in FAIMS Using Spectral Normalization 

FIGURE 3.49 Normalized mean FAIMS separation parameters for ubiquitin ions (z = 6, 7) in N2 gas over 7=35-80 °C, measured at u=15 (A), 20 ( ), and 25 ( ) kV/cm. For each D. we show the first-order regressions through all data (solid lines) and those for T — 50-80 °C (dashed lines). (From Robinson, E.W., Shvartsburg, A.A., Tang, K., Smith, R.D., Anal. Chem. 80, 7508, 2008.) The vertical displacements of datasets for adjacent d values that provide the best coincidence of regressions are labeled (in °C). 

4 Varying the Ion Heating in FAIMS and Suppressing Ion Transformations in Cryo-FAIMS  

Understanding of the drivers (3.5.2 and 3.5.3) for often undesirable (3.5.1) heat-induced reactions in FAIMS allows devising strategies for their suppression. Decreasing Ed that reduces heating in proportion to by Equation 3.73 generally does not work because the separation power drops more, in proportion to E and commonly faster because of the terms with 1 in Ec(Ed) expansion (3.2.3). 

Equation 3.73 might counsel one to suppress the heating by switching to a gas where ion mobihlies are lower, such as CO2 or SF compared to N2. While that decreases Th at constant E/N, the difference for macroions is by a factor of (01/02), where lii and 0,2 are the values of fi in the two gases (1.3.9). As the 

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