Mass Spectrometry
-
Upload
cecilia-anthony -
Category
Documents
-
view
52 -
download
0
description
Transcript of Mass Spectrometry
![Page 1: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/1.jpg)
Mass SpectrometryMass spectrometry involves ionizing a compound, separating the ions that result on the basis of mass to charge ratio (m/z) and obtaining a plot of number of ions (abundance) versus m/z.
![Page 2: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/2.jpg)
Example Mass Spectrum
![Page 3: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/3.jpg)
Ionization Methods
![Page 4: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/4.jpg)
EI = Electron ImpactVapor-phase sample molecules are bombarded with high energy electrons (70 eV). This causes the sample molecules to eject an electron forming a radical cation.
Ionization potential of typical compound < 15 eV. Therefore, extensive bond breaking occurs resulting in smaller cations and radicals.
![Page 5: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/5.jpg)
Example of EI MS
![Page 6: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/6.jpg)
CI = Chemical IonizationChemical ionization is a “soft” ionization method. Much less bond breaking occurs than in EI.
Vapor phase sample molecules are mixed with a reagent gas such as CH4, or NH3. The reagent gas molecules are ionized by electron impact and then the resulting molecular ions of the reagent gas molecules react with the sample molecules.
R + e R+. + 2e R+. + RH RH+ + R.
RH+ + S SH+ + R RH+ + S RSH+
(R = reagent, S = sample, e = electron, . = radical electron , H = hydrogen):
SH+ iis the sample molecule plus one proton – m/z = M+1It is not a radical-cation (it is an even-electron species) and was not produced by excess ionizing voltage. It remains relatively intact – does not fragment.
![Page 7: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/7.jpg)
Example of CI MS
![Page 8: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/8.jpg)
FAB = Fast Atom BombardmentUses high-energy (6-10keV) Xe or Ar atoms to bombard samples dissolved in a high-boiling liquid (“matrix” often glycerol). Results in protonated sample molecules (MH+) with little fragmentation. Also see peaks due to matrix ionization and subsequent reactions. Useful for high MW compounds that will not work under CI or EI conditions.
FD = Field Desorption
Carbon microneedles on the surface of a metal emitter with which sample molecules come in contact. High voltage gradients at the tips of the microneedles remove an electron from the sample molecule which is repelled away from the emitter. Molecular ions with little excess energy are generated.
![Page 9: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/9.jpg)
Example of FD MS
![Page 10: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/10.jpg)
ES = Electrospray
![Page 11: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/11.jpg)
ES MS of a Protein
![Page 12: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/12.jpg)
Ionization Methods Summary
![Page 13: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/13.jpg)
Ion Separation Methods
![Page 14: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/14.jpg)
Rotating Sector
![Page 15: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/15.jpg)
Quadrupole
![Page 16: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/16.jpg)
Ion Trap
http://www.chm.bris.ac.uk/ms/theory/qit-massspec.html
![Page 17: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/17.jpg)
Summary of Mass Analyzers
http://masspec.scripps.edu/information/intro/chapter3.html
![Page 18: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/18.jpg)
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
![Page 19: Mass Spectrometry](https://reader031.fdocuments.net/reader031/viewer/2022032206/5681327e550346895d9918db/html5/thumbnails/19.jpg)
PhMe2Si
Ts
SePh
HRMS FAB+ = 542.1203
Example