ADVANCED TECHNIQUES FOR THE DIFFERENTIATION OF ISOMERS BY MASS SPECTROMETRY

Mass spectrometry (MS) is a powerful and widespread technique but is inherently uncapable to differentiate species with same m/z ratio. For this reason, many classical approaches were developed based on differential fragmentation patterns in tandem MS. More recently, new techniques for isomer identification in MS were developed, and we highlight the photodissociation techniques that will be discussed in this review. This photodissociation techniques explore the selective activation of isomers to induce isomer specific dissociations in the gas-phase that depend on the spectroscopic features of the isomers. If tunable radiation sources are available, this selective activation may be monitored as a function of the radiation wavelength, allowing the acquisition of vibrational or UV-Vis spectra of the isolated ions, making it possible to evaluate different isomers, protomers and even conformers by MS. These photodissociation techniques are even more powerful when coupled to ion mobility techniques, that will be briefly discussed. Because these techniques enhance the fields and analytical applications where MS can be used, this review will discuss the classical MS methods for isomer differentiation that lead to the fundamentals of ion spectroscopy and selective ion activation, with emphasis on the vibrational ion spectroscopy.