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Mass Spectrometry II

Mass Spectrometry II. Isotopes: HRMS and recognition of isotope patterns. 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 79.916250. Example of HRMS for formula proof.

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Mass Spectrometry II

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  1. 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 79.916250

  3. Example of HRMS for formula proof HRMS FAB = 542.1203 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 C6H14 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.

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