Determination of oligonucleotide deamination by high resolution mass spectrometry

A novel analytical approach capable of measuring deaminated degradation products of oligonucleotide therapeutics is described. The method employs high-resolution mass spectrometry to assess the shift in isotopic distribution that accompanies deamination. Isotopic Distribution Factors (IDF), derived directly from the peak heights of the isotopic pattern, are employed to measure deamination levels of as little as 0.5%. Results obtained from application of the method to a phosphorothioate diester oligonucleotide exposed to various temperatures were used to determine deamination rates.