1. Isotopes: HRMS and recognition of isotope patterns
Mass Spectrometry II
Isotopes: HRMS and recognition of isotope patterns

2. High Resolution - HR MS
Determination of exact mass using HR MS has mostly supplanted combustion analysis as a way of proving molecular formula for new compounds.
Selenium

3. Example of HRMS for formula proof
HRMS FAB =
Reviewer Assignment : Does the provided FAB MS data provide acceptable proof of molecular formula? Justify your reasoning quantitatively (show calculation).

4. Example 2
Assignment : Decide whether the ESI-TOF mass spectrum at left provides acceptable proof of molecular formula. Justify your reasoning quantitatively (show calculation).

5. Appendix 1A

6. Isotope Patterns
Notice that in the MS of methane there is a small peak at M+1.

7. Effect of # of C’s on M+1 peak
C6H C10H18

8. Organic Bromides

9. Dibromides

10. Tribromides

11. Organic Chlorides

12. Dichlorides

13. Isotope Patterns in General
N, O, F, I, Si, and P are all essentially monoisotopic (so no isotope patterns)
C is somewhat monoisotopic but with large numbers M+1 peaks become significant.
S is 95% 32S, 5% 34S
Se gives cool patterns
For the presence of >1 of a diisotopic element use polynomial expansion to predict pattern: (a + b)n
Software for isotope pattern and HRMS calculations exist.