Deconvoluting Isotopic Distributions to Evaluate Parent/Fragment Ion Relationships

Traditionally, the broad isotopic distributions typical of most large molecules are seen as an impediment to the use of tandem mass spectrometry (MS/MS) for the sequencing of large biomolecules because they complicate fragment‐ion spectra making them difficult to interpret. Clearly, if very large molecules are to be analyzed by MS/MS there is a need for methods of analysis that take into account the isotopic distributions of fragment ions. The present paper shows how to rigorously deconvolute the isotopic distribution of a leaving group whose chemical formula is postulated from a parent ion, whose isotopic distribution may be available from an experimental mass spectrum, giving, in the process, the isotopic distribution of a fragment ion. It is not necessary to know the chemical formula of either the parent ion or the fragment ion. This calculation is potentially useful because the deconvoluted spectrum can then be compared with the experimentally acquired fragment‐ion mass spectrum in order to aid in the assignment of the spectrum. © 1997 John Wiley & Sons, Ltd.