Analyses in Mixed Gas Buffers

FIGURE 3.33 The behavior of Eq for Cs in mixed gases Blanc in N2/O2 (a) and non-Blanc in He/N2 (b) or He/C02 (c). (From Shvartsburg, A.A., Tang, K., Smith, R.D., Anal. Chem., 76, 7366, 2004.) Circles are measurements ( d = 20 kV/cm), hues are calculations using Blanc s law (dotted) and the high-field mobility theory for gas mixtures (solid or dashed). In (b, c), calculations ate also shown for lower Ejy, as labeled. 

When aU aj are small, Equation 3.65 may be approximated to the first order as 

Mixtures of only He, N2, and CO2 were tried in real FAIMS work so far, and compositions involving other gases will likely improve many existing and future applications. An ideal FAIMS buffer would (i) be a binary mixture of gases that form very dissimilar potentials with ions of interest, (ii) resistelectrical breakdown, and (iii) as a practical matter, be chemically inert and comprise stable, mutually nonreactive, readily available, and not too costly components. To avoid condensation and facilitate 

FIGURE 3.35 Separation parameters of o-, m-, and p-phthalic acid anions in N2/CO2 with variable CO2 concentration (at ambient conditions) using d= 16.5 kV/cm, the Ec spectrum of the mixture of three isomers measured at 5% CO2 is in the inset. (Adapted from Barnett, D.A., Purves, R.W., Ells, B., Guevremont, R., J. Mass Spectrom., 35, 976, 2000.) 

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