Structural Characterization of Unsaturated Phosphatidylcholines Using Traveling Wave Ion Mobility Spectrometry

Abstract

A number of phosphatidylcholine (PC) cations spanning a mass range of 400 to 1000 Da are investigated using electrospray ionization mass spectrometry coupled with traveling wave ion mobility spectrometry (TWIMS). A high correlation between mass and mobility is demonstrated with saturated phosphatidylcholine cations in N2. A significant deviation from this mass-mobility correlation line is observed for the unsaturated PC cation. We found that the double bond in the acyl chain causes a 5% reduction in drift time. The drift time is reduced at a rate of ~1% for each additional double bond. Theoretical collision cross sections of PC cations exhibit good agreement with experimentally evaluated values. Collision cross sections are determined using the recently derived relationship between mobility and drift time in TWIMS stacked ring ion guide (SRIG) and compared to estimate collision cross-sections using empiric calibration method. Computational analysis was performed using the modified trajectory (TJ) method with nonspherical N2 molecules as the drift gas. The difference between estimated collision cross-sections and theoretical collision cross-sections of PC cations is related to the sensitivity of the PC cation collision cross-sections to the details of the ion-neutral interactions. The origin of the observed correlation and deviation between mass and mobility of PC cations is discussed in terms of the structural rigidity of these molecules using molecular dynamic simulations.

Linking molecular models with ion mobility experiments. Illustration with a rigid nucleic acid structure

“…[88,90] All were initially parameterized to evaluate Ω CALC with helium collision gas. Several optimizations either of the calculation algorithm or of the parameterization, [45,91,92] including for nitrogen collision gas, [93,94] have been proposed. This section aims at clarifying these variations.…”

Assessment of altered lipid homeostasis by HILIC-ion mobility-mass spectrometry-based lipidomics

“…When ion mobility is coupled with mass spectrometry, a two-dimensional separation is achieved on the basis of the CCS-to-charge (/z) and the mass-to-charge (m/z), respectively. Several ion mobility (IM)-MS techniques have been applied to lipidomic analysis, including drift tube ion mobility (DTIM) (25)(26)(27), traveling wave ion mobility (TWIM) (28,29), and differential mobility spectrometry (DMS) (30)(31)(32). In DTIM-MS, the ions travel through the neutral gas-filled drift tube under a low and static electric field, which leads to separation of ions on the scale of micro-to milliseconds (21).…”

Characterization of acyl chain position in unsaturated phosphatidylcholines using differential mobility-mass spectrometry

“…In a recent critical evaluation of the current tools for lipidomics, some of us have suggested that differentiation of isomeric lipids could be achieved by combining IMS and MS workfl ows ( 12 ), considering that different IMS technologies have previously been deployed for lipid analysis ( 32 ). For example, Jackson et al ( 33 ) successfully separated GP classes using drift tube IMS followed by MS identifi cation, while Kim and colleagues ( 34 ) showed some resolution of PCs based on the degree of unsaturation using traveling-wave IMS. To this point, however, there have been no reports of the application of IMS to resolving sn -positional isomers in GPs.…”