Spectrus: Evaluating isotope patterns to support molecular formula assignment in xC/UV/MS data

Description
Isotope patterns in MS spectra (e.g., for Cl, Br, S) help confirm proposed molecular formulas. Spectrus supports viewing and comparing theoretical and experimental isotope patterns.

Solution

1. In Spectrus, display the mass spectrum for the ion of interest.
2. Identify the isotopic cluster (e.g., M, M+2, M+4 peaks).
3. Right click on the parent peak and select Formulae Generator:
   • Set elemental composition constraints (C, H, N, O, halogens, etc.).
   • Include an accurate mass (if available) and set tolerances.
   • Select Run. A Table of Formulae will appear. Close the Formulae Generator window.
4. Compare generated formulae to experimental isotope patterns:
   • Right click in the active spectrum and ensure the Calculate Isotope Clusters option is checked.
   • Zoom into the region of interest in the mass spectrum.
   • Select a proposed formula from the Table of Formulae and compare the generated isotope clusters (overlayed in red) to the experimental spectrum.
5. Assess agreement:
   • Choose the formula whose theoretical pattern best matches the experimental data.