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Molecular Mass Spectrometry

Molecular Mass Spectrometry. Mass Spectroscopy (MS). The elemental composition of matter of samples The structure of inorganic, organic and biological molecules The quantitative and qualitative composition of complex mixture Isotopic ratios of atoms in samples. MS - Components.

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Molecular Mass Spectrometry

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  1. Molecular Mass Spectrometry

  2. Mass Spectroscopy (MS) • The elemental composition of matter of samples • The structure of inorganic, organic and biological molecules • The quantitative and qualitative composition of complex mixture • Isotopic ratios of atoms in samples

  3. MS - Components Components of Mass Spectrometer

  4. GC/MS System Components

  5. MS - Ionization • Gas phase ionization (103 D): • Electron Impact (EI) – Energetic electron beam • Chemical Ionization (CI) – Reagent gaseous ions • Field Ionization (FI) – high potential electrode

  6. MS - Ionization • Desorption Ionization (105 D): • Field Desorption (FD) – High- potential Electrode • Electrospray Ionization (ESI) – High Electric Field (20 kV) • Matrix – Assisted Desorption/Ionization (MALDI) • Plasma desorption (PD) – Fission fragments from 252Cf • Thermospray ionization (TS) – High temperature

  7. MS - Ionization • Hard source – enough energy to rupture bonds and producing fragments (EI) • Soft source – provides always molecular weight of the molecule (CI; ESI, MALDI)

  8. MS – Electron-Impact Ionization

  9. MS – Ionization Chamber

  10. MS – Ring Component Spectrum

  11. MS - Spectra CH2Cl2 MW=84 1-Pentanol MW=88

  12. MS - Chromatogram

  13. MS – Isotopes Abundance Most Other Percentage (%) H1 H2 0.015 C12 C13 1.08 N14 N15 0.37 S32 S33 0.8 S34 4.4 Cl35 Cl37 32.5 Br79 Br81 98.0 Si28 Si29 5.1 Si30 3.4

  14. MS – Effect of Ionization Mode on Spectra EI Field Desorption Field Ionization Glutamic Acid HOOC-CHNH2 -CH2 – CH2 - COOH

  15. MS – Ionization Mode and Spectra Electron- Impact 1- Decanol MW = 158 Chemical Ionization

  16. MS – Chemical Ionization • Most often use reagent is CH4: • Electrons will form several ions: CH4+; CH3+; CH2+ • Reactions (MH – sample molecule): CH4+ + CH4 CH5+ + CH3 CH5+ + MHMH2+ + CH4 (M + 1) CH3+ + CH4 C2H5+ + H2 C2H5+ + MH M+ + C2H6 (M – 1) (M + 29)

  17. GC/MS – Jet Separator

  18. GC/LC/MSSample Transfer

  19. MS – Direct Sample Introduction External Sample Introduction System Direct Sample Probe

  20. MS – Mass Analyzer • Resolution: R = m/Dm Where: m – mass of the first peak Dm – difference between two adjacent peaks Commercial MS have resolution 500 to 500,000 Dm = m/R

  21. MS Analyzer – Magnetic Sector

  22. MS – Electromagnetic Analyzer

  23. Quadrupole MS Analyzer

  24. MS – Quadrupole Filter

  25. MS - Ion Trap Analyzer

  26. MS – Time of Flight Analyser

  27. MS – Reflectron Time of Flight Analyzer

  28. MS – Fourier Transform Analyzer Ion Cyclotron Resonance Magnetic Field

  29. GCMS - Instrumentation

  30. MS - Instrumentation

  31. LCMS – Electrospray Ionization (ESI)

  32. MS – Capillary Electrophoresis

  33. MS – Supercritical Chromatography

  34. MS – Ion Detector

  35. MS/MS

  36. MS/MS Instrumentation

  37. MS - Cost

  38. Mass Spectrum MW 240 5-Ethyl-5n-hexyl barbituric acid

  39. MS - Chromatogram

  40. MS - Quantitative • SIM – single ion monitoring • Spectra mode • Precision – 2% to 10%

  41. MS – Spectra Interpretation • Base peaks and Relative Ion Intensities: • Determine molecular ion mass. CI if needed. • Elemental composition from isotopic abundance: • Look for A+2 pattern elements (Cl, Br, S, Si, O) • Check A+1 ratios for absence/presence of S and Si • Use the nitrogen rule to determine number of N’s (If MW is even N=0 or even number. If MW is odd = odd number of nitrogen atoms • Estimate number of H, F, I, and P from isotopic ratios and MW balance (P is multivalent; F=19; I=127 mass units) • Check allowance for rings and double bonds. Number of double bonds or rings = x – 1/2y +1/2 z +1 (x=C, Si; y=H, F, Br, Cl; z=N, P, O, S)

  42. MS – Spectra Interpretation • Use molecular ion fragmentation mechanism: • Check fragment masses differences for expected losses (Cl = 35; Br=79; Me=15; Et=29 etc…) • Look for expected substructures • Look for stable neutral loss (CH2 == CHR) • Look for products of known rearrangements • Postulate structures: • Search library data base • Run hit compound on the same instrument to confirm • Use MS/MS if further confirmation is needed

  43. MS - Applications

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