M+2 and M+4 Peak Calculator: Isotope Pattern of Chlorine, Bromine and Sulfur Compounds
Isotope Pattern of the Molecular Ion Peak: Chlorine, Bromine and Sulfur
This calculator shows the isotope pattern of the molecular ion peak in a mass spectrum when a compound contains chlorine, bromine or sulfur. Choose the number of atoms, and it draws the M, M+2, M+4 and M+6 peaks and gives the ratio of their heights.
Chlorine, bromine and sulfur each have a heavier isotope that is two mass units above the lighter one, so a compound containing them gives more than one molecular ion peak.
Chlorine, Bromine and Sulfur Isotope Pattern Calculator: M, M+2 and M+4 Peaks
What it is for: this calculator shows the shape of the molecular ion peak in a mass spectrum when a compound contains chlorine, bromine or sulfur atoms. It draws the M, M+2, M+4 and M+6 peaks and gives the ratio of their heights.
How to use it
- Choose a common case, such as 1 Cl, 2 Br or 1 Cl + 1 Br, with one click.
- Or set the number of chlorine, bromine, sulfur and carbon atoms yourself with the plus and minus buttons.
- Look at the graph: the purple bar is the M peak and the orange bars are the isotope peaks.
- Read the observation below the graph for the ratio of the peaks, and the table for the exact heights.
Step 1Choose a common case
Step 2Or set the number of atoms yourself
Step 3Look at the isotope pattern
Step 4Read the observation
| Peak | Relative height (%) | Main isotopes in this peak |
|---|
Heights are calculated from the natural abundance of the isotopes: chlorine-35 75.8% and chlorine-37 24.2%; bromine-79 50.7% and bromine-81 49.3%; sulfur-32 95.0%, sulfur-33 0.75% and sulfur-34 4.25%; carbon-13 1.07%. The tallest peak of the group is set to 100%.
Summary: The isotope pattern of the molecular ion peak shows which of these elements a compound contains. One chlorine atom gives M and M+2 peaks in a ratio of about 3:1, one bromine atom gives them in a ratio of about 1:1, and one sulfur atom gives a small M+2 peak of about 4.5%. Two or three halogen atoms add M+4 and M+6 peaks. For the full explanation, read the article on the M+2 peak and isotope patterns in mass spectrometry.
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