Linking lasers and mass spectrometers: Investigating CID+UV as a new fragmentation tool for analytical chemistry of biomolecules

Fragmentation methods in tandem mass spectrometry are of critical importance for the analysis of biomolecular ions, and the development of new tools to effect fragmentation is therefore an area of great current interest. In this thesis, a potential new tool for initiating biomolecule fragmentation is investigated. This method combines low-energy collision induced dissociation, CID, with UV diode (375 nm) irradiation as a single fragmentation tool, named CID+UV. Initial experiments were conducted on the nucleobases uracil, adenine, thymine and cytosine complexed to an iodide ion. The results showed a significant increase in the amount of depletion of I-·uracil and I-·adenine using CID+UV when compared to conventional low-energy CID fragmentation, while I-.thymine and I-·cytosine showed no detectable enhanced depletion. To further investigate the possible fragmentation processes operating, UV laser photodissociation spectra of the I-·uracil and I-·thymine clusters were obtained. These spectra displayed strong absorptions associated with excitation of nucleobase centred chromophores, associated with production of an I- photofragment. CID+UV fragmentation was also tested as a fragmentation tool on the proteins melittin and angiotensin I human acetate. Melittin proved to be unsuitable for the experimental setup due to its m/z being beyond the range of the mass spectrometer. Angiotensin I human acetate showed several peaks unique for the CID+UV mass spectrum against the conventional CID results, demonstrating the potential of the new CID+UV as a new fragmentation tool.