A program is described, which allows the intensity contributions from naturally occurring heavy isotopes to be eliminated from the mass spectrometric ions of an artificially labelled compound. This allows the accurate measurement of the isotopomer distribution of the compound and hence its percentage isotopic abundance. In the case of radioactively labelled compounds the specific radioactivity can then be derived from the abundance data. The program utilizes a graphical user interface based upon the C++ Builder 6.0 environment and VCL library.