Modeling of isotopomeric cluster of the molecular ion.

The occurrence of poly-isotopic elements in a molecule or ion can result in complex isotopomeric cluster of an ion. The "isotopomer" better and correctly indicates different isotopic compositions of a molecule (compound) or ion and not a single atom. The ions of organic compounds show in accurate mass spectra single, isolated peaks or narrow sub-clusters regardless of their molecular masses. The occurrence of a PIE makes the molecular ion cluster more complex and significantly influences the location of the most abundant peak and the form of the cluster. The present study is an attempt at answering the following question: what is the mechanism of the molecular ion's isotopomeric cluster formation and is it step-by-step predictable? The accurate mass-resolved isotopomer cluster can be predicted from accurate masses and abundances of the stable isotopes. The cluster consists of several sub-patterns, each of which is composed of near signals (at the same nominal m/z). The range of the sub-cluster usually does not exceed 0.005 u. The low-resolution cluster can be predicted from the high-resolution pattern by addition of all peaks occurring over a given narrow mass range (m/z - 0.5; m/z+0.49). Surprisingly, predicting the accurate mass cluster is simpler than predicting the low-resolution one. A compliance of the model results with the experimental ones suggests a correct prediction.