We present the use of drug-like molecules as a traveling wave (T-wave) ion mobility (IM) calibration sample set, covering the m/z range of 122.1-609.3, the nitrogen collision cross-section (ωN 2) range of 124.5-254.3 Å 2 and the helium collision cross-section (ω He) range of 63.0-178.8 Å 2. Absolute ωN 2 and ω He values for the drug-like calibrants and two diastereomers were measured using a drift-tube instrument with radio frequency (RF) ion confinement. T-wave drift-times for the protonated diastereomers betamethasone and dexamethasone are reproducibly different. Calibration of these drift-times yields T-wave ωN 2 values of 189.4 and 190.4 Å 2, respectively. These results demonstrate the ability of T-wave IM spectrometry to differentiate diastereomers differing in ωN 2 value by only 1 Å 2, even though the resolution of these IM experiments were ∼40 (ω/δω). Demonstrated through density functional theory optimized geometries and ionic electrostatic surface potential analysis, the small but measurable mobility difference between the two diastereomers is mainly due to short-range van der Waals interactions with the neutral buffer gas and not long-range charge-induced dipole interactions. The experimental RF-confining drift-tube and T-wave ωN 2 values were also evaluated using a nitrogen based trajectory method, optimized for T-wave operating temperature and pressures, incorporating additional scaling factors to the Lennard-Jones potentials. Experimental ω He values were also compared to the original and optimized helium based trajectory methods.
ASJC Scopus subject areas
- Analytical Chemistry