Abstract
Negative chemical ionization(NCI) mass Spectra of a number of nucleosides, halogenonucleosides and purine and pyrimidine bases have been studied using a H2/N2O mixed gas as a reagent gas. In most of the nucleosides, each base fragment ion (b)- peak was the strongest, (M-H)- ion peak was weak or non-existent, and a significant (b+O)- ion was found. It seems that formation of the (b+O)- ion roughly correlates to the LUMO energy of corresponding base. A group of low mass ions (m/z 71, 58, 45) which was attributed to the sugar moiety cleavage was clearly found in ribonucleosides, but not in 2′-deoxyribonucleosides. NCI spectra of the halogenonucleosides showed the prominent peaks of halogen ions (often the base peak). Molecular ion M- was formed from these halogenonucleosides. The process of negative ion production of nucleosides was discussed.
