Mass spectrometry protonated aromatic molecule

Recent experimental developments in coupling IR spectroscopy techniques with mass spectrometry, which allow the structural characterization of isolated and microsolvated protonated aromatic molecules in the gas phase have been summarized.64 Hydrogen-deuterium exchange has been observed at Ha in (59) and some closely related substrates when this ligand is complexed to Cu1 in [2Hg]acetone.65 The process is finely controlled by the precise coordination distance required to form agostic interaction between Cu(I) and the C-H bond and is believed to involve the enol form of [2H6]acetone and a reversible Cu(I) to Cu(III) interconversion. 

Mass spectrometry is a fairly universal technique it is a label-free detection technique and can be applied to any molecule as long as it can be ionized (i.e. that it presents a protonation site for instance). Optical techniques (e.g. UV absorbance and fluorescence-based techniques) require that the analytes present given properties to be detected. They must absorb or emit in the UV or in the fluorescence range. If they do not, they must be coupled to an external moiety (aromatic group, fluorophore) that presents such absorption/emission properties, and this imposes an additional derivatization of the analytes before their detection, but after their separation for instance... 

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