Optimization of the design and operation of FAIMS analyzers

Shvartsburg, Alexandre A.; Tang, Keqi; Smith, Richard D.

doi:10.1016/j.jasms.2004.09.009

Cited by 75 publications

(147 citation statements)

References 52 publications

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“…In c-FAIMS, filtering out ions with CVs outside of a finite range allowing equilibrium in the gap requires a certain t res (∼50 ms in Selectra), and further FAIMS action does not improve resolution. 47 In p-FAIMS, there is a single CV permitting ion equilibrium, and ions with even a tiny CV difference will eventually be eliminated given sufficient time. Hence, longer separation times would increase R (in principle) indefinitely.…”

Section: Simulations As a Function Of Faims Analyzer Curvature And Thmentioning

confidence: 99%

High-Resolution Field Asymmetric Waveform Ion Mobility Spectrometry Using New Planar Geometry Analyzers

2006

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Field asymmetric waveform ion mobility spectrometry (FAIMS) has emerged as a powerful tool of broad utility for separation and characterization of gas-phase ions, especially in conjunction with mass spectrometry (MS). In FAIMS, ions are filtered by the dependence of mobility on electric field while carried by gas flow through the analytical gap between two electrodes of either planar (p-) or cylindrical (c-) geometry. Most FAIMS/MS systems employ c-FAIMS because of its ease of coupling to MS, yet the merits of two geometries have not been compared in detail. Here, a priori simulations reveal that reducing the FAIMS curvature always improves resolution at equal sensitivity. In particular, the resolving power of p-FAIMS exceeds that of c-FAIMS, typically by a factor of 2 -4 depending on the ion species and carrier gas. We have constructed a new planar FAIMS incorporating a curtain plate interface for effective operation with an ESI ion source and joined to MS using an ion funnel interface with a novel slit aperture. The resolution increases up to 4-fold over existing c-FAIMS, even though the analysis is ∼2 times faster. This allows separation of species not feasible in previous FAIMS studies, e.g., protonated leucine and isoleucine or new bradykinin isomers. The improvement for protein conformers (of ubiquitin) is less significant, possibly because of multiple unresolved geometries.

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Section: Simulations As a Function Of Faims Analyzer Curvature And Thmentioning

confidence: 99%

High-Resolution Field Asymmetric Waveform Ion Mobility Spectrometry Using New Planar Geometry Analyzers

2006

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“…The underlying physical model incorporates ion diffusion (accounting for the high-field and anisotropic components) and space charge [38]. Calculations for resolution and sensitivity have previously been compared with measurements for a variety of systems across a wide range of ion sizes/types and FAIMS operational regimes and conditions [38,39]. We have used this capability to probe the dependence of FAIMS response on several design and operational parameters, including g, L, w c , form of V D (t), and the identity and flow velocity of buffer gas [39].…”

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confidence: 99%

“…Calculations for resolution and sensitivity have previously been compared with measurements for a variety of systems across a wide range of ion sizes/types and FAIMS operational regimes and conditions [38,39]. We have used this capability to probe the dependence of FAIMS response on several design and operational parameters, including g, L, w c , form of V D (t), and the identity and flow velocity of buffer gas [39]. Elucidating the key trends as a function of these variables has allowed the FAIMS performance to be optimized depending on specific analytical priorities [39].…”

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confidence: 99%

“…We have used this capability to probe the dependence of FAIMS response on several design and operational parameters, including g, L, w c , form of V D (t), and the identity and flow velocity of buffer gas [39]. Elucidating the key trends as a function of these variables has allowed the FAIMS performance to be optimized depending on specific analytical priorities [39].…”

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confidence: 99%

“…The response depends on the ion current that controls the magnitude of space-charge effects, but all possibilities are encompassed by the limits of zero current (where those are absent) and saturated current (where the FAIMS charge capacity is filled and excess incoming ions are rapidly eliminated by Coulomb repulsion) [38,39]. All simulations described are for pure buffer gases, but could be extended to gas mixtures via the formalism that accounts for non-Blanc effects on FAIMS separations [41].…”

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FAIMS operation for realistic gas flow profile and asymmetric waveforms including electronic noise and ripple

Shvartsburg

Tang

Smith

2005

J. Am. Soc. Mass Spectrom.

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The use of field asymmetric waveform ion mobility spectrometry (FAIMS) has rapidly grown with the advent of commercial FAIMS systems coupled to mass spectrometry. However, many fundamental aspects of FAIMS remain obscure, hindering its technological improvement and expansion of analytical utility. Recently, we developed a comprehensive numerical simulation approach to FAIMS that can handle any device geometry and operating conditions. The formalism was originally set up in one dimension for a uniform gas flow and limited to ideal asymmetric voltage waveforms. Here we extend the model to account for a realistic gas flow velocity distribution in the analytical gap, axial ion diffusion, and waveform imperfections (e.g., noise and ripple). The nonuniformity of the gas flow velocity profile has only a minor effect, slightly improving resolution. Waveform perturbations are significant even at very low levels, in some cases ϳ0.01% of the nominal voltage. These perturbations always improve resolution and decrease sensitivity, a trade-off controllable by variation of noise or ripple amplitude. This trade-off is physically inferior to that obtained by adjusting the gap width and/or asymmetric waveform frequency. However, the disadvantage is negligible when the perturbation period is much shorter than the residence time in FAIMS, and ripple adjustment appears to offer a practical method for modifying FAIMS resolution. S eparation of ions in the gas-phase using field asymmetric waveform ion mobility spectrometry (FAIMS) extends back two decades [1][2][3][4][5][6][7]. However, FAIMS was not widely used until its coupling to electrospray ionization mass spectrometry [8,9], which has expanded its utility to environmental [10 -13] and biological [14 -18] applications, in addition to traditional detection of airborne volatiles [19 -23]. The recent advent of commercial FAIMS systems (Ionalytics Selectra [17,24] and Sionex DMS [23,25]) is increasing the acceptance of FAIMS and diversifying its applications.While FAIMS analyses have become increasingly common, the fundamentals remain relatively poorly understood [18]. Phenomenologically, ions are separated by the difference between mobilities at high and low electric fields (E) (respectively K H and K L ) that in general differ as ion mobilities in gases depend on the field. Thus, FAIMS measures the mean derivative of mobility with respect to field ͗ѨK⁄ѨE͘ (over a certain range of E), in contrast to the conventional ion mobility spectrometry [26,27] that determines absolute mobilities (K). The K(E) function can be expressed as a polynomial over even powers of E/N, where N is the buffer gas number density [28,29]:Mobilities tend to significantly deviate from zero-field values K(0) at E/N Ն ϳ30 to 40 Td, which defines the lower limit for electric fields useful in FAIMS operation. The upper limit is given by the onset of electrical breakdown in gas, which depends on the gas identity and number density, and (to a lesser extent) the width and geometry of the gap between electrodes (the...

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