A method has been developed for high field asymmetric ion mobility spectrometry (FAIMS) using varying percent helium. FAIMS separates gas phase ions based on the difference of their mobilities in high and low electric fields. Most FAIMS analyzers use pure nitrogen as a carrier gas due to the convenience of combining FAIMS with electrospray ionization (ESI) sources which commonly use nitrogen as the nebulizer and drying gas. However, the addition of alternate gases into the nitrogen flow has been shown to significantly increase the resolution of FAIMS devices. Helium is the lowest mass and least polarizable gas used in FAIMS separations and increases the low field mobility. The use of helium increases the resolution but at the same time decreases sensitivity for low mass-to-charge ions because of increased transmission loss due to radial diffusion. A scan linking compensation voltage (CV) and percent helium composition balances signal and resolution over a range of mass-to-charge values. This method has successfully scanned varying percent helium compositions to separate a sample as well as two conformations of one of the ions within the sample.
• Scanning mode reduces ion losses associated with using helium while significantly increasing resolving power over traditional CV scans
• Changing the percent helium composition also alters the FAIMS waveform which alters separation
- Improved Differential Ion Mobility Separations Using Linked Scans of Carrier Gas Composition and Compensation Field J. Am. Soc. Mass Spectrom. (2015) 26:1746-1753