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Mass Spectroscopy (MS) Separation of ions in gas phase based on different mass to charge ratios (m/z) Differing movement in electric (E) and/or magnetic.

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Presentation on theme: "Mass Spectroscopy (MS) Separation of ions in gas phase based on different mass to charge ratios (m/z) Differing movement in electric (E) and/or magnetic."— Presentation transcript:

1 Mass Spectroscopy (MS) Separation of ions in gas phase based on different mass to charge ratios (m/z) Differing movement in electric (E) and/or magnetic (B) fields Molecular ion gives molecular weight Fragmentation to identify molecule (fingerprint); or high-resolution Peaks for different isotopes are easily observed even at low-res

2 MS originated with cathode ray experiments in late 1800’s; electrical discharge (plasma) in a sealed tube ~1900 Wien showed cathode rays could be deflected by a magnetic field 1913 JJ Thomson (1897 proved existence of electron using cathode ray exps) did 1 st mass spec Ne—1 st proof of isotopes

3 ESA Electrostatic analyzer (KE filter) -2 curved metal plates w DC voltage (+) ion sees two forces, electrostatic force and centripetal force -separates by KE

4 FW Aston (student of Thomson) won Nobel Prize for compiling data of isotopes and abundances for elements Said “MS is dead” once he finished isotopes ~1919 double focussing MS

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9 Electron impact vs chemical ionization

10 Ion Sources: 1. Electron Impact (EI) M + e -  M  e - ~1 in a million ionized Lots of fragmentation—advantage in i.d. Sometimes no molecular ion 2. Chemical Ionization (CI) Methane in EI source CH 4 + e -  CH e - (same as EI); also CH 3 + formed Lots of ion-molecule rxns CH CH 4  CH CH 3 CH CH 4  C 2 H H 2 Lots of CH 5 + and C 2 H 5 + C 2 H M  MH + + C 2 H 4 (proton transfer; get peak at (M+1) + ) C 2 H M  (M-H) + + C 2 H 6 (hydride transfer; get peak at (M-1) + ) Soft ionization source, less fragmentation, molecular ions at (M+1) + and (M-1) +


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