Adduct ion formation as a tool for the molecular structure assessment of ten isomers in traveling wave and trapped ion mobility spectrometry

Abstract

Rationale The separation of isomeric compounds with major differences in their physiochemical and pharmacokinetic properties is of particular importance in pharmaceutical R&D. However, the structural assessment and separation of these compounds with current analytical techniques and methods are still a challenge. In this study, we describe strategies to separate the various structural and stereo‐isomers. Methods The separation of ten structural and stereo‐isomers was investigated using Trapped and Travelling Wave ion mobility spectrometry (TIMS and TWIMS). Different strategies including adduct ion formation with Na, Li, Ag and Cs as well as fragmentation before and after the ion mobility cell were applied to separate the isomeric compounds. Results All the counter ions (in particular Na) strongly coordinated with the test analytes in all the IMS systems. The highest resolving power was achieved for the sodium and lithium adducts using TIMS‐time‐of‐flight (TOF). However, some separation was attained on a Synapt HDMS system with its unique potential to monitor the ion mobility of the product ions. The elution order of the adduct ions was the same in all instruments, in which, unexpectedly, the para‐substituted isomer of the [M + Na]+ species had the lowest collision cross section followed by the meta‐ and ortho‐isomers. Conclusions The formation of adduct ions could facilitate the separation of structural and even stereo‐isomers by generating different molecular conformations. In addition, fragmenting isomers before or after the ion mobility cell is a valuable strategy to separate and also to assess the structures of adducts and different conformers.

Enantio‐separation of pregabalin by ternary complexation using trapped ion mobility spectrometry

“…Unfortunately, pregabalin enantiomers were not recognized by TIMS‐TOF MS (Figure S1, supporting information). Based on the literature, 22,26,30,38,39 the addition of alkali or transition cations could greatly increase the separation efficiency of isomeric compounds, prompting us to enhance the resolution of pregabalin enantiomers by preparing the ternary complexes of CD with pregabalin enantiomers and alkali‐earth cations.…”

“…Over the past decades, ion mobility mass spectrometry (IM‐MS) has been developed as a promising method for differentiating isomer molecules due to the differences in ion mobility of different isomers 20–24 . To separate multiple pairs of enantiomers, Dwivedi et al 25 employed (S)‐(+)‐2‐butanol as a chiral modifier using drift tube ion mobility mass spectrometry (DTIM‐MS).…”

“…[16][17][18][19] Over the past decades, ion mobility mass spectrometry (IM-MS) has been developed as a promising method for differentiating isomer molecules due to the differences in ion mobility of different isomers. [20][21][22][23][24] To separate multiple pairs of enantiomers, Dwivedi et al 25 employed (S)-(+)-2-butanol as a chiral modifier using drift tube ion mobility mass spectrometry (DTIM-MS). After that, a more powerful IM-MS tool, trapped ion mobility spectrometry (TIMS), was introduced by Femandez-Lima et al 20 In 2018, Pérez-Míguez et al 26 successfully distinguished amino acid enantiomers by TIMS after derivatization of chiral amino acids with (+)-1-(9-fluorenyl) ethyl chloroformate.…”

“…Unfortunately, pregabalin enantiomers were not recognized by TIMS-TOF MS (FigureS1, supporting information). Based on the literature,22,26,30,38,39 the addition of alkali or transition cations could greatly increase the separation efficiency of isomeric compounds, prompting us to enhance the resolution of pregabalin enantiomers by preparing the ternary complexes of CD with pregabalin enantiomers and alkali-earth cations.Thus, the Ca 2+ ternary complexes, including [α-CD + pregabalin + Ca − H] + , [β-CD + pregabalin + Ca − H] + , and [γ-CD + pregabalin + Ca − H] + , were analyzed by TIMS-MS TOF. The mobilograms are shown in Figure 4.…”

Ion mobility spectrometry-tandem mass spectrometry strategies for the on-line monitoring of a continuous microflow reaction

“…The IMS can surpass the limitations of LC by rapid (millisecond timescale) separation of isomeric compounds with high selectivity and improved signal-tonoise ratio [13]. Moreover, the separation of molecular ions based on their Collision Cross Section (CCS), size, shape, and charge by IMS enables elucidating structural information [14,15]. Combined with MS/MS, the fragmentation pathways add to the potential to unambiguously assign the molecular structure of unknowns.…”