FAIMS separation parameters

TRENDS OF FAIMS SEPARATION PARAMETERS 3.3.1 How Should FAIMS Data Be Reported ... 

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). 

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). 

Reducing the pressure in curved FAIMS may materially change separation parameters because of Dehmelt force, which may be a benefit or a problem (4.3.8). This effect may necessitate limiting reduced-pressure FAIMS to planar gaps. 

The separation parameters in HOD IMS will depend on the gas temperature as in FAIMS (3.3.4) here, the effect should generally be stronger because of the inherently greater nonlinearity of HOD IMS mechanism and rise for higher separation orders. For example, the thermal variation of a for benzene and o-toluidine cations in air increases at higher n for the former, heating from 10 °C to 40 °C changes by 7%, a2 by -70%, and by > 300% (Table 5.1). 

This chapter has described the use of asymmetric waveforms to separate and identify ion species based on the dependence of mobility on electric field intensity. We have reviewed the mechanism of differential mobility effect, the ways to quantify and maximize its magnitude, and the associated processes and limitations for various ion types. Understanding those issues allows us to start exploring and optimizing the performance of FAIMS systems depending on the instmmental parameters and ion properties. 

Separation Performance of FAIMS and Its Control via Instrumental Parameters... 

In summary, the sensitivity and resolving power of flow-driven planar FAIMS at moderate ion current scale as the inverse exponent and square root of separation time ties, respectively. These laws allow predicting many aspects of analyses without simulations and permit their validation when simulations are needed. The variation of ties via adjustment of flow rate is an effective practical approach to control of planar FAIMS resolution. In strongly curved gaps, ties is less important and other instmmental parameters make a greater difference (4.3). 

Dependence oe Separation Metrics on Instrument Parameters IN Curved FAIMS... 

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