Mass Spectrometry.pptx chemistry m. Phil

Mass Spectrometry.pptx chemistry m. Phil

• 1.
  Mass Spectrometry by Dr AbdullahIjaz Hussain
• 2.
  Mass Spectrometry  ADestructive Technique  Important toll for structure elucidation of unknown compounds  Give information about molecular weight  Give information about the fragments  Also coupled with other techniques like GC (GCMS), LC (LCMS), ICP (ICPMS) etc
• 3.
  Coupling GC withMS
• 4.
  Component of MassSpectrometer  Ion source  Mass analyzers  Ion detector  Read out Devices
• 5.
  MS Components
• 6.
  Ion Sources  ElectronImpact Ionization (EI)  Chemical Ionization (CI)  Field Ionization (FI)
• 7.
  EI, CI  EI(hard ionization)  Gas-phase molecules enter source through heated probe or GC column  70 eV electrons bombard molecules forming M+* ions that fragment in unique reproducible way to form a collection of fragment ions  EI spectra can be matched to library stds  CI (soft ionization)  Higher pressure of methane leaked into the source (mtorr)  Reagent ions transfer proton to analyte
• 9.
  EI process  M+ e- M+* f1 f2 f3 f4 This is a remarkably reproducible process. M will fragment in the same pattern every time using a 70 eV electron beam
• 10.
  CI/ ion-molecule reaction 2CH4 + e-  CH5 + and C2H5 +  CH5 + + M  MH+ + CH4  The excess energy in MH+ is the difference in proton affinities between methane and M, usually not enough to give extensive fragmentation
• 11.
  Mass Analyzer  Quardropolemass analyzer  Single focussing magnetic analyzer  Double focussing magnetic analyzer  Ion Trap  Time of flight
• 12.
  Mass Analyzers  Lowresolution  Quadrupole  Ion trap  High resolution  TOF time of flight  Sector instruments (magnet)  Ultra high resolution  ICR ion cyclotron resonance
• 13.
  Quadrupole Mass IonFilter
• 14.
  Types of MassAnalyzers Magnetic Sector: Single Focusing: A magnetic field is used to focus ions based on their momentum as they are ejected from an ion source at high energy. Resolution <2000 Focuses based on momentum
• 15.
  Magnetic sector doublefocusing: An electrostatic analyzer is used serially with a magnet to select monoenergetic ions. High resolution >10,000 mass up to 100,000Da
• 16.
  Ion Trap
• 17.
  Time of Flight-TOF
• 18.
  Where: • mi = massof analyte ion • zi = charge on analyte ion • E = extraction field • ti = time-of-flight of ion • ls = length of the source • ld = length of the field-free drift region • e = electronic charge (1.6022x10-19 C)
• 19.
  Ion Collector
• 20.
  Interpretation of MassSpectra  The peak of highest M/z is the molecular ion peak and it gives the molecular weight of compound.  The peak of highest intensity about 100% is the base peak and it is due to most stable ion.  Meta stable ion peaks appear on some non integral value of M/z and give information about the mechanism of fragmentation
• 21.
  M+ /z M+ /z Fragments Intensity (%)M/z [CH3-CH2-CH2-CH2-CH2-CH3]+ 35 86 [CH3-CH2-CH2-CH2-CH2]+ 10 71 [CH3-CH2-CH2-CH2]+ 100 57 [CH3-CH2-CH2]+ 75 43 [CH3-CH2]+ 40 29 MS spectrum of n-hexane
• 22.
  Applications of GC-MS Determination of mass, molecular formula and structure of compounds  Qualitative and quantitative analysis  In petroleum industry analysis of crude petroleum products  Food industry  Analysis o f pesticides residues  Plastic industry  Fertilizers analysis