Abstract
Ion mobility mass spectrometry experiments enable the characterization of mass, assembly, and shape of biological molecules and assemblies. Here, a new radio-frequency confining drift cell is characterized and used to measure the mobilities of peptide, protein, and protein complex ions. The new drift cell replaced the traveling-wave ion mobility cell in a Waters Synapt G2 HDMS. Methods for operating the drift cell and determining collision cross section values using this experimental set up are presented within the context of the original instrument control software. Collision cross sections for 349 cations and anions are reported, 155 of which are for ions that have not been characterized previously using ion mobility. The values for the remaining ions are similar to those determined using a previous radio-frequency confining drift cell and drift tubes without radial confinement. Using this device under 2 Torr of helium gas and an optimized drift voltage, denatured and native-like ions exhibited average apparent resolving powers of 14.2 and 16.5, respectively. For ions with high mobility, which are also low in mass, the apparent resolving power is limited by contributions from ion gating. In contrast, the arrival-time distributions of low-mobility, native-like ions are not well explained using only contributions from ion gating and diffusion. For those species, the widths of arrival-time distributions are most consistent with the presence of multiple structures in the gas phase.
Highlights
Ion mobility has grown in popularity as a powerful gas-phase technique capable of rapid, efficient separation and structural characterization.[1]
Ion mobility has been used for the analysis of explosives,[2] peptides,[3] proteins,[4] protein complexes,[5,6,7,8,9,10] and other biomolecules.[11]. Many variations of this gas-phase technique exist that use different gas compositions, pressures, and electric fields, but are all designed to leverage differences in gas-phase ion transport that depend on shape and charge
A new RF-confining drift cell was developed and implemented in a Waters Synapt G2 HDMS. This device has been shown to yield precise and accurate Ω values for a broad mass range of peptide, protein, and protein complex ions. This device yields Ω values that are very similar to those measured using a previous RF-confining drift cell (0.3% average difference) or DC-only drift tubes (0.6% average difference)
Summary
Ion mobility has grown in popularity as a powerful gas-phase technique capable of rapid, efficient separation and structural characterization.[1]. Traditional ion mobility experiments measure the drift times of ions in a neutral background gas (typically helium, nitrogen, or air) under a weak electric field. These ion mobility experiments are usually operated in a low-field regime, in which the mobility of the ion (K, cm[2] V−1 s−1) is independent of the applied drift field strength (V cm−1 Torr−1).[15]. Traditional “direct-current-only” (DC-only) ion mobility drift tubes are composed of a series of ring electrodes with an applied DC voltage that changes linearly along the length of the drift tube.[16,17,18,19,20] The diffusion-limited resolving power depends on the thermal diffusion along the axis of transmission:[21,22]
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