IMPROVED ELECTROSPRAY IONIZATION OF SYNTHETIC OLIGODEOXYNUCLEOTIDES

A method is described for rapid purification of synthetic oligodeoxynucleotides to remove sodium counter ions prior to electrospray ionization mass spectrometry. The oligomers, following purification by gel electrophoresis, are precipitated from ammonium acetate to replace sodium ions by ammonium ions, and dissolved in water. Negative-ion electrospray spectra are presented for oligomers with up to 48 residues in which the most intense peaks correspond to the [M - nH]n- ion. The spectrum of 77-mer (M(r) 24 039) shows the predominant peak as due to retention of only a single sodium ion. Changes in the spectra are reported for different instrument orifice voltages and different solution pH. The method should permit rapid, accurate analysis of most typical, synthetic oligodeoxynucleotides.