PTR Method Using H3O+ ( Ionisation of analyte by proton transfer from H3O+ )
Photograph showing the PTR section with its multiple plate electrodes and the electron impact source on the right side.
Close-up photograph of the glow discharge source and PTR section, with cover removed.
Chemical Ionisation by Ion Molecule Reaction
Kr+ ( 13.99 eV ) + CO → CO+ ( 13.98 eV ) + Kr ( Chemical Ionisation by Ion-Molecule Reaction )
Example: SO2 Monioring Argon has an ionisation energy of 15.76eV. SO2 has an ionisation energy of 12.32eV, thus should be ionised in a collision with Ar+.
Adjacent is data acquired from a 50ppm SO2 in Nitrogen sample. 100,000 c/s were at mass 65 for this analyte using Ar+
Electron Impact Ionisation ( EI Mode )
The instrument features a conventional electron impact ionisation source in the high vacuum section. When an analyte of interest cannot be ionised by the proton transfer method, the glow discharge source may be switched off and the electron impact source activated. Electron impact ionisation is a very common method, and a large database of EI spectra exists ( NIST database ). All components are ionised by this method, but the excess of energy does result in fragmentation. At times this can be useful for identifying a compound.