Ultrafast Differential Ion Mobility Spectrometry at Extreme Electric Fields Coupled to Mass Spectrometry

Abstract

Microchip-based field asymmetric waveform ion mobility spectrometry (FAIMS) analyzers featuring a grid of 35 µm -wide channels have allowed electric field intensity (E) over 60 kV/cm, or about twice that in previous devices with >0.5 mm gaps. Since the separation speed scales as E 4 to E 6 , these chips filter ions in just ~20 µs (or ~100 -10,000 times faster than "macroscopic" designs), although with reduced resolution. Here we report integration of these chips into electrospray ionization (ESI) mass spectrometry, with ESI coupled to FAIMS via a curtain plate/orifice interface with edgewise ion injection into the gap. Adjusting gas flows in the system permits control of ion residence time in FAIMS, which affects resolving power independently of ion desolvation after the ESI source. The results agree with a priori simulations and scaling rules. Applications illustrated include analyses of amino acids and peptides. Because of limited resolving power, the present FAIMS units are suitable to distinguish compound classes more than individual species. In particular, peptides separate from many other classes, including PEGs that are commonly encountered in proteomic analyses. In practical analyses with realistic time constraints, the effective separation power of present FAIMS may approach that of "macroscopic" systems.

Cryogenic Methods for the Spectroscopy of Large, Biomolecular Ions

“…Other FAIMS devices have achieved higher resolution by using longer ion residence times [169], higher fields [171,172], or different separation gas [172,173]. However, in most of these cases, the degree of heating of the ions caused by the separation fields increases, and this can cause conformer isomerization.…”

Comparison of the peak capacity for DMS filters with various gap height: experimental and simulations results

“…The effective gap improved significantly when the frequency increased to 30 MHz, or the spacing of the DMS electrodes increased. Commercial DMS devices from Owlstone have a very narrow gap height and operate in the high frequency regime [14][15][16]. Experiments were conducted with 10 peptides from a BSA digest, to further determine if high separation fields could compensate for limited gap height.…”

“…The spacing between the parallel plates in a DMS analyzer can be generally referred to as the gap height (h). The literature contains examples of numerous atmospheric pressure DMS devices that include gap heights ranging from approximately 35 μm [14][15][16] to 2 mm [17,18]. Three of these publications have attempted to compare the separation capability of devices with different gap heights.…”

“…While the peak capacity appeared to be greater with the 0.5 mm filter, it is hard to draw conclusions from these data as the separation waveform and transport gas humidity were different. Shvartsburg also compared the separation of 3 peptides using a 35 μm DMS filter and a larger gap Bplanar macroFAIMS^at different separation fields, using different generator configurations [15]. The larger gap height device provided approximately 4X greater peak capacity, however, the authors were not able to directly compare data from the 2 systems because the devices used different waveform shapes and amplitudes.…”

Pulsed electron beams in ion mobility spectrometry

“…These sources were also examined in order to have non-radioactive alternatives because of the technical, organizational and related financial complications that accompany the application of radioactive substances. Regarding the voltage schemes, in particular high-field asymmetric field ion mobility spectrometry (FAIMS) (Klaassen et al 2009, Shvartsburg et al 2009, Schneider et al 2010, Barnett and Oullette 2011 has attracted a lot of interest in recent years.…”