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Advanced Mass Spectrometry for Molecular Formula Determination

Learn about High Resolution Mass Spectrometry (HRMS) and recognition of isotope patterns for exact mass determination, replacing combustion analysis. Explore HRMS examples like Selenium-79 and FAB data analysis. Quantitatively justify molecular formula proof using provided mass spectra data. Understand the impact of different carbon numbers on isotope patterns. Discover software for isotope pattern and HRMS calculations.

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Advanced Mass Spectrometry for Molecular Formula Determination

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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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