Photoionization used in Py-MS

Photoionization is not a common technique in mass spectrometry, but it was reported to be utilized for both Py-GC/MS [61, 62] and for Py-MS [61]. Compared to El spectra, for which extended mass spectral libraries are available, the photoionization (PI) spectra are not standard and therefore not library searchable. However, the ionization being softer, the molecular ion is commonly more intense providing additional information in certain cases when the El mass spectrum is not diagnostic. 

A photoionization system usually consists of a windowless, differentially pumped rare gas resonance lamp coupled with the ionization chamber of the mass spectrometer. Argon, krypton, or other inert gases are used in the lamp. Energies of 11.6 and 11.8 (Ar I) eV are produced by argon, and 10.0 and 10.6 (Kr I) eV for krypton. The pressure inside the ion source is usually about 10 Torr. 

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