GCMS of Kerosene

1
GC/MS of Kerosene

• Basic Principles of MS with an Application to
  GC/MS of Kerosene

2
MS PRINCIPLES IFundamental Molecular Processes

• Ionization
• RR' e- ---gt R?R 2e-
• parent ion
• Fragmentation
• R?R' ---gt R ?R'

3
MS PRINCIPLES IIParent Peak

• Parent Peak
• Mass of parent ion is molecular mass, not
  molecular weight.
• Except for isotope peaks, parent peak is usually
  peak of highest mass number. MH for P 1
  possible if heteroatom is present.
• Prominent parent peaks
• Aromatics
• Conjugated olefins
• Short-chain hydrocarbons
• Poor parent peaks
• Aliphatic alcohols, amines, nitrites, nitrate,
  nitro compounds, nitriles, highly branched
  compounds

Mass spectra of a normal alkane and a branched
alkane (Click on the icon)
4
MS PRINCIPLES III Fragmentation Patterns for
alkanes

• Unimolecular decompositions (low P)
• Peaks at 14n 1
• Most intense fragments at C3 and C4
• Branched alkanes show different fragmentation
  patterns due to stability of sec and tert
  carbonium ions.
• Branch alkanes exhibit smaller parent ion peak.

5
MS PRINCIPLES IVFragmentation Rules

• Relative height of parent peak is greatest for
  straight chain, decreases with branching.
• Relative height of parent peak usually decreases
  with increasing molecular weight in homologous
  series.
• Cleavage is favored at branched carbon atom

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Sample Data for Standards and Kerosene

• Click on the Acrobat icon to view the following
  pages
• Total ion chromatograms for C11-C14 standard and
  kerosene
• Mass spectra for C13H28 and C14H30. Note that
  retention times correspond to peaks in standard
  run
• Peak report for standard
• Peak report for kerosene
• Table showing calculation of response factors