Specific radioactivity determinations of ionic organic compounds of high specific activity by fast atom bombardment and field desorption mass spectrometry

Carbon‐14 and tritium labelled ionic organic compounds such as quaternary ammonium salts, steroid sulphates, bile acid conjugates, and oligopeptides have been analyzed for their label distribution and for their specific radioactivity by fast atom bombardment and field desorption mass spectrometry. No significant differences between the quantitative results with both techniques are found. The minimal specific radioactivities detectable by this approach are about 20 MBq mmol−1 or 10 GBq mmol−1 for compounds labelled with one atom of carbon‐14 or one atom of tritium per molecule, respectively. Specific radioactivity determinations of highly labelled biochemicals are characterized by a precision and an accuracy in the region between 1% and 5%.