²⁵²Cf-plasma desorption mass spectrometry of chemically protected ribo- and deoxyribooligonucleotides

Abstract

A new method of determining the base sequence, the purity and the molecular weight of a chemically protected ribo- or deoxyribooligonucleotide is described. Using the method ²⁵²Cf-plasma desorption mass spectrometry positive and negative ion mass spectra have been obtained of a variety of protected oligonucleotides ranging from the simplest mononucleotide unit to the tetradecanucleotide level. The ²⁵²Cf-PD positive ion spectrum is generally dominated by the presence of molecular ion species in the mass range above 350 M/z. The negative ion spectrum is characterized by the presence of two nested sets of fragment ions formed by the random cleavage of C3'-03' and C5'-05' internucleotidic bonds. Each set therefore contains ions which extend from the 3'- or 5'-terminal mononucleotide to the level of the intact molecular ion. It is thereby possible from an analysis of the ²⁵²Cf-PD negative ion spectrum to unequivocably determine the base sequence of the fully protected oligonucleotide. These results have also demonstrated that ²⁵²Cf-PDMS can be used to produce and detect ions up to 12,600 M/z.