Isomeric and Conformational Analysis of Small Drug and Drug-Like Molecules by Ion Mobility-Mass Spectrometry (IM-MS)

Abstract

This chapter provides a broad overview of ion mobility-mass spectrometry (IM-MS) and its applications in separation science, with a focus on pharmaceutical applications. A general overview of fundamental ion mobility (IM) theory is provided with descriptions of several contemporary instrument platforms which are available commercially (i.e., drift tube and traveling wave IM). Recent applications of IM-MS toward the evaluation of structural isomers are highlighted and placed in the context of both a separation and characterization perspective. We conclude this chapter with a guided reference protocol for obtaining routine IM-MS spectra on a commercially available uniform-field IM-MS.

Keywords: Conformation; Drugs; IM-MS; Ion mobility spectrometry; Ion mobility-mass spectrometry; Isomers.

Fig. 1

Structures related to four constitutional isomers of chemical formula C₈H₉NO₂ and corresponding function or typical use

Fig. 2

(a) Block diagram of a typical IM-MS instrument. Ions are separated in the presence of a neutral drift gas by (b) a linear electric field along a series of ring electrodes (DTIMS) or (c) by a pulse wave generated by applied sequential voltage along a series of ring electrodes (TWIMS)

Fig. 3

(a) Leucine/isoleucine isomers with chemical formula C₆H₁₃NO₂ examined in this study. Experimental cross sections with respective standard deviations are shown at the right with corresponding stereochemistry. (b) (I) Experimental IM spectrum overlays for all isomer compounds (standard error bars omitted for clarity). (II) Overlay of the IM spectra corresponding to N,N-dimethylglycine ethyl ester, l-tert-leucine, and l-norleucine and the IM spectrum corresponding to the mixture (black). (III) Overlays of l-isoleucine and l-leucine in addition to the equal ratio mixture. (IV and V) Overlays of diastereomers and enantiomers, respectively. Adapted with permission from ref. , Copyright 2017 American Chemical Society

Fig. 4

Complexity of carbohydrate isomers represented graphically pertaining to both constitutional isomers (connectivity isomers) and stereoisomers (axial/equatorial substitutions, chair/boat conformations, and α/β glycosidic linkage orientation)

Fig. 5

Drift time profiles of (R) and (S) thalidomide enantiomers with corresponding CCS observed in both positive and negative mode (a and b, respectively) for nitrogen drift gas. Structures are illustrated at the bottom for chiral reference

Fig. 6

Agilent MassHunter Workstation Data Acquisition Program tune page with callouts for various commands

Fig. 7

Sample run dialogue box including file directory information and sample name

Fig. 8

Agilent MassHunter IM-MS Browser interface. (a) Mass spectrum of thalidomide, (b) drift spectra window with expanded window for thalidomide drift profile, and (c) 2-D IM-MS window with callout of the thalidomide [M+H]⁺ ion species