ELECTROSPRAY COLLISION-INDUCED DISSOCIATION MASS-SPECTRA OF POSITIVELY CHARGED OLIGONUCLEOTIDES

Positive ion collision-induced dissociation (CID) mass spectra of olig onucleotides provide qualitatively similar fragmentation patterns td C ID mass spectra generated from negative ion precursors. The major sequ ence ion series w and a-base are still abundant enough to be useful fo r the determination of the sequence of an oligonucleotide. The applica tion of sequencing to both positively and negatively charged precursor ions up to the 20-mer level are shown. The positive ion electrospray charge-state distributions are found to be sensitive to the base compo sition of the oligonucleotide. In the case of homopolymers containing the bases adenine, guanine and cytodine the average charge state is fo und to be similar. However, the average charge state of a homopolymer containing the base thy-mine is significantly lower, In addition, the CID mass spectra of this oligonucleotide results in the formation of x -2H and z-2H type ions exclusively, These differences are thought to b e caused due to the phosphate backbone being the site of protonation r ather than the base. (C) 1997 by John Whey & Sons, Ltd.