Atmospheric pressure photoionization (APPI) is a soft ionization technique that is typically preferred for certain polar and non-polar compounds. In APPI, an ion is generated from a molecule when it interacts with a photon from a light source, such as the Syagen™ Technology PhotoMate™ APPI™ light source. APPI generates molecular ions for molecules that have an ionization potential less than the photon energy of the light being emitted by the light source.
Molecules that include steroids, basic-drug entities, and pesticides have ionization potentials below the threshold. APPI reduces fragmentation because only a small amount of energy is deposited in the molecule. Molecules, such as those in the nitrogen, sheath and auxiliary gas and the simple solvents used for LC/MS, are not ionized because their ionization potentials are greater than the photon energy. The result is selective ionization of an analyte versus the background.