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Russell Rouseff

mass spectrometry II. FOS 6355 Summer 2005. Russell Rouseff. Isotope Abundances. 16 O (~99.76%) 17 O (0.04%) 18 O (0.20%) 12 C (~98.9%) 13 C (~1.1%) 35 Cl (75.77%) and 37 Cl (24.23%) 35.4527 79 Br (50.50%) and 81 Br (49.50%) 79.904. 12.0107 Amu. High Resolution MS.

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Russell Rouseff

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  1. mass spectrometry II FOS 6355 Summer 2005 Russell Rouseff

  2. Isotope Abundances • 16O (~99.76%) • 17O (0.04%) • 18O (0.20%) • 12C (~98.9%) • 13C (~1.1%) • 35Cl (75.77%) and 37Cl (24.23%) 35.4527 • 79Br (50.50%) and 81Br (49.50%) 79.904 12.0107 Amu

  3. High Resolution MS Molecular ion M+ = 84.0937 C6H12 Possible compounds ?? C5H8O Establishes molecular formula of unknown

  4. IR-MS • Mass spectrometry is also used to determine the isotopic composition of elements within a sample. Differences in mass among isotopes of an element are very small, and the less abundant isotopes of an element are typically very rare, so a very sensitive instrument is required. These instruments are called isotope ratio mass spectrometers (IR-MS) and use a single magnet to bend a beam of ionized particles towards a series of cups which convert particle impacts to electric current.

  5. Menthol Peppermint Oil

  6. Time of Flight MS

  7. Time of Flight MS

  8. Ion Trap MS

  9. Ion Trap Limitations • Requires careful quantitation • Limited dynamic range • Subject to space charge effects and ion molecule reactions • No sensitivity gain using SIM

  10. Vanillin - quadrupole

  11. Vanillin – Ion Trap

  12. Unpasteurized NFC GFJ TIC Intensity 20.5 20.6 20.7 20.8 20.9 21 21.1 21.2 21.3 21.4 21.5 Retention Time (min)

  13. Unpasteurized NFC GFJ TIC Isopropyl Hexanoate o Allo-Ocimene o Intensity 20.5 20.6 20.7 20.8 20.9 21 21.1 21.2 21.3 21.4 21.5 Retention Time (min)

  14. MS/MS

  15. Vanillin – Ion Trap MS/MS

  16. SIM

  17. EIC

  18. Spectral Analysis

  19. Common Fragments

  20. Linear Alkanes • Loss CH3 first - 15 • Then ethene groups – C2H4 (28) or methlene CH2 (14) • branched alkanes from more stable carbocations

  21. Decane

  22. Esters, Acids and Amides • Loss of group attached to carbonyl, X group • forms substituted oxonium ion From carboxylic acids From unsubstituted amides

  23. Alcohols • Lose hydrogen and hydroxyl radical • Also lose a-alkyl (or H) groups, forms oxonium ions R1 and R2 in a position

  24. Aromatic Hydrocarbons • forms “aromatic cluster”, m+, m-1, m/e = 65 • benzyl carbocation forms tropylium ion, then loss of acetylene = m/e 65 benzyl carbocation

  25. Aldehydes and Ketones • Major cleavage – loss of one side chain (ketones) • generates substituted oxonium ion • McLafferty rearrangement • loss of neutral ethene – C2H4

  26. Ethers • Lose methyl group – CH3 M-15 • forms substituted oxonium ion

  27. Halides • Simple loss of halogen • molecular ions of Cl and Br show “halide pair” • 35Cl/37Cl ratio is roughly 3.08:1 • 79Br/81Br ratio is 1.02:1

  28. 64 100 28 29 27 50 66 26 49 51 63 65 35 48 61 30 50 37 59 67 32 41 39 44 52 0 20 24 28 32 36 40 44 48 52 56 60 64 68 Ethyl Chloride Unknown Halide Spectrum

  29. Unknown Formula = C5H12O

  30. Examples • Vanilla comparison • Identification of rose oil volatiles

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