Atmospheric pressure photoionization mass spectrometry of nucleic bases, ribonucleosides and ribonucleotides

Almost all the ionization techniques have been employed for the analysis of the bases, nucleosides and nucleotides in mass spectrometry, except atmospheric pressure photoionization (APPI). The latter has attracted these last years a growing interest for the analysis of biological molecules. In this work, we report a comprehensive study of the ionization mechanisms under APPI conditions of the bases, nucleotides and nucleosides. In-source fragmentations have been studied first with the photoionization lamp switched off, i.e., under thermospray conditions. It is shown that, in this mode of operation, fragmentations are minor and the compounds do not suffer from thermal degradation. The fragmentation patterns of these biomolecules have been further monitored under both direct and dopant-assisted photoionization conditions for three different dopant molecules (toluene, anisole and acetone). Some fragmentation channels appeared to be dependent on the nature of the dopant employed and the versatility of the fragments generated under APPI conditions originates from the formation of a variety of precursor ions in the ion source.