Distortion of Ion Structures by Field Asymmetric Waveform Ion Mobility Spectrometry

Journal Article · Thu Feb 15 04:00:00 EST 2007 · Analytical Chemistry, 79(4):1523-1528

DOI:https://doi.org/10.1021/ac061306c· OSTI ID:901751

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

Field asymmetric waveform ion mobility spectrometry (FAIMS) is emerging as a major analytical tool, especially in conjunction with mass spectrometry (MS) and/or conventional ion mobility spectrometry (IMS). In particular, FAIMS is used to separate protein or peptide conformers prior to characterization by IMS, MS/MS, or H/D exchange. High electric fields in FAIMS induce ion heating, previously estimated at <10 0C on average and believed too weak to affect ion geometries. Here we use a FAIMS/IMS/MS system to compare the IMS spectra for ESI-generated ubiquitin ions that have and have not passed FAIMS, and find that some unfolding occurs for all charge states. The analysis of those data and their comparison with reported protein unfolding in a Paul trap indicate that at least some structural transitions observed in FAIMS, or previously in an ion trap, are not spontaneous. The observed unfolding is overall similar to that produced by heating of ~40 - 50 0C above room temperature, consistent with the calculated heating of ions at FAIMS waveform peaks. Hence the isomerization in FAIMS likely proceeds in steps during “hot” periods, especially right after ions entering the device. That process distorts ion geometries and causes ion losses by a “self-cleaning” mechanism, and thus should be suppressed as much as possible. We propose achieving that via cooling FAIMS by the amount of ion heating; in most relevant cases cooling by ~75 0C should suffice.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 901751
• Report Number(s): PNNL-SA-50928; 20496; 400412000
• Journal Information: Analytical Chemistry, 79(4):1523-1528, Journal Name: Analytical Chemistry, 79(4):1523-1528 Journal Issue: 4 Vol. 79
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory
FAIMS
IMS
protein structure