Application of ESI-FAIMS-MS to the analysis of tryptic peptides

High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates gas-phase analyte ions from chemical background, offering substantial improvements in the detection of peptides from complex protein digests. For a digest of enolase 1 (baker's yeast), the focusing and separation offered by FAIMS produced an average intensity gain of 3.5 for the tryptic ions and reductions in background intensity of 5- to 10-fold when compared with ESI-MS. The increased signal-to-background in the ESI-FAIMS-MS experiment resulted in a greater number of identifiable peptides and therefore greater sequence coverage. Compensation voltage (CV) maps for a total of 282 tryptic peptides from thirteen proteins, generated according to charge-state, mass-to-charge ratios, and chain length, show that a majority of tryptic peptides can be detected by operating FAIMS at a few discrete values of CV rather than scanning CV across a wide range. The ability to reduce scanning requirements has potential benefits for coupling FAIMS with LC-MS. In select cases, FAIMS can be used to eliminate isobaric MS overlap between tryptic peptides; however, the primary advantage of FAIMS in an LC-FAIMS-MS analysis is foreseen to be the attenuation of chemical background noise rather than the separation of individual peptides. Using FAIMS to reduce mass spectral noise will offer improved detection of peptides from low abundance proteins in complex biological samples.