The combination of laser photodissociation, action spectroscopy, and mass spectrometry to identify and separate isomers

Abstract

The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been deployed to tackle...

Monitoring intramolecular proton transfer with ion mobility-mass spectrometry and in-source ion activation

“…3,4 However, since in the case of intramolecular proton migration, the same molecule acts as both the donor and acceptor species, there are limitations for experimental studies as methods must be able to discriminate between two or more isomers protonated from different sites (i.e., protomeric isomers, or ''protomers''). To this end, spectroscopic and spectrometric techniques such as photodissociation spectroscopy, 5 IR multiphoton dissociation, 6 ion mobility-mass spectrometry (IM-MS), 7 or combination of them 8 have been applied in recent years for experimental discrimination and characterisation of protomers in the gas phase. Furthermore, computational methods are generally used independently or alongside these experimental techniques for investigation of intramolecular proton transfer.…”

“…, protomeric isomers, or “protomers”). To this end, spectroscopic and spectrometric techniques such as photodissociation spectroscopy, 5 IR multiphoton dissociation, 6 ion mobility-mass spectrometry (IM-MS), 7 or combination of them 8 have been applied in recent years for experimental discrimination and characterisation of protomers in the gas phase. Furthermore, computational methods are generally used independently or alongside these experimental techniques for investigation of intramolecular proton transfer.…”

Mechanism of formation and ion mobility separation of protomers and deprotomers of diaminobenzoic acids and aminophthalic acids

“…2,3 Of particular interest is the protonation/ deprotonation of compounds with more than one basic/acidic site leading to the formation of isomers that are protonated/ deprotonated at different sites, so-called prototropic isomers that are frequently referred to as protomers and deprotomers, respectively. 4 Studies of such systems can take advantage of a limited range of techniques including infrared multiphoton dissociation (IRMPD), 5,6 UV-vis photodissociation (PD) spectroscopy, 7,8 and ion mobility-mass spectrometry (IM-MS), 9 which are used in combination with computational methods [10][11][12] to assign the charge location and to perform gas phase analysis. Among these experimental techniques, IM-MS performed in hybrid instrumentation is particularly attractive as it allows both separation of isomeric ions and independent MS and MS/ MS studies to be performed.…”

Protomers of the green and cyan fluorescent protein chromophores investigated using action spectroscopy

“…10,11 In solution and in the gas phase, the protonated forms of these chromophores, pHBDI + and Cyan + , can exist as several protomers (protonation isomers), which may exhibit distinct photophysical properties. 12 Characterisation of protomers (or deprotomers for anions) and probing the impact of protonation site on molecular photophysics is a topical area in gas-phase spectroscopy due to the emerging analytical capabilities to separate and probe protomers; 13 such selectivity is almost always impossible in solution due to rapid proton exchange, with solution experiments measuring some solvent-dependent average.…”

“…12 Isomer selectivity in action spectroscopy experiments is most commonly achieved by incorporating ion mobility as a separation dimension. 13,19 While the occurrence of coexisting protomers is becoming a common theme in gas-phase spectroscopy, general trends or 'rules of thumb' for the preponderance of protomers can be difficult to determine because, aside from the electrospray solvent, relative protomer yields can depend on a vast number of factors including solution pH, electrospray geometry and needle voltage, desolvation conditions, and collisional treatment of ions as they are introduced into vacuum. 20,21 Additionally, because most gas-phase action spectroscopy instruments are custom designed, it can be difficult to know if the protomer distribution generated in one experiment is the same as for another.…”