Isotoppatterner

Isotoppatterner, or isotopic patterns, describe how the signals of a molecule in mass spectrometry are distributed among a series of peaks that arise from different isotopic compositions. The main peak (M) corresponds to the all-light-isotope molecule, while additional peaks (M+1, M+2, etc.) reflect substitutions of atoms by heavier isotopes such as 13C, 15N, 17O or 18O. The shape and height of the pattern depend on the element composition and their natural abundances.

Each element contributes its own characteristic distribution. Carbon, for example, creates an M+1 peak roughly proportional to the number of carbon atoms, since about 1.1% of carbon is 13C. Elements with multiple stable isotopes can create more pronounced shoulders or shoulders at higher mass differences. Chlorine and bromine are particularly notable: chlorine produces an M+2 peak about one-third the height of the main peak due to the 35Cl/37Cl pair, while bromine yields nearly equal M and M+2 peaks because its isotopes 79Br and 81Br occur in similar abundances. Sulfur, nitrogen, and oxygen contribute additional M+2 and higher peaks depending on their isotopic compositions.

Theoretical isotopic patterns are generated by combining, or convolving, the isotope distributions of all elements in the molecule. In high-resolution mass spectrometry, comparing observed patterns with calculated ones aids in determining or validating molecular formulas and can help identify the presence of specific elements or functional groups. Limitations include peak overlap, noise, and instrument calibration, which can complicate interpretation. Software tools can simulate and fit isotopic patterns to proposed formulas to assist analysis.