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OnCampusRates2002.pdf
OffCampusRates2002.pdf
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The Finnigan MAT95, a double focusing high resolution instrument, is located
in room 1203 of the Henry Eyring Building (North). This instrument is used for
the majority of the analyses.
Features
- Nominal Mass Scanning - up to 3500 amu
- Accurate Mass Analysis - Electrical Scanning or Peak Matching
- Electron Impact Ionization
Electron impact ionization (EI) is the classical ionization
method used in mass spectrometry. Samples are thermally desorbed (standard
solids probe, high temperature probe) or introduced through a gas
chromatograph and thus must be thermally stable. EI is a highly informative
method as it provides fragmentation information in addition to molecular
weight. In may cases a library search can be used to assist in structural
identification.
- Chemical Ionization (Methane or Isobutane)
Chemical ionization (CI) is a complementary technique to EI.
Sample introduction is that same of EI so this method is limited to thermally
stable compounds. The ion source is maintained at high pressure with a CI
reagent gas such as methane or isobutane and the spectrum shows a
quasimolecular ion with little or no fragmentation. CI is a soft ionization
method used to get the molecular weight of a thermally stable, volatile
compounds.
Fast atom bombardment (FAB) is a soft ionization method, and
like CI provides quasimolecular information with little or no fragmentation.
FAB is used for many thermally unstable, non-volatile compounds. The sample is
dissolved in a solvent and matrix a placed on a FAB probe target. The target
is introduced into the ion source and the sample, solvent, matrix combination
is bombarded with energetic Cs ions often with the result of protonation of
the sample. After desolation and removal of the matrix in the vacuum system
the analyte is detected and analyzed. FAB is used to get the molecular weight
of polar, often large molecular weight, non-volatile compounds. Caution must
be taken to clean up the sample including removal of salts.
- Positive and Negative Switching (CI and FAB)
[ LCQ Classic (new!) ] [ Micromass Quattro II ] [ HP MS Detector ] [ Finnigan MAT 95 ]
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