Atmospheric-pressure laser ionization

Atmospheric pressure laser ionization is an atmospheric pressure ionization method for mass spectrometry (MS). Laser light in the UV range is used to ionize molecules in a resonance-enhanced multiphoton ionization (REMPI) process. It is a selective and sensitive ionization method for aromatic and polyaromatic compounds. Atmospheric photoionization is the latest in development of atmospheric ionization methods. Atmospheric pressure laser ionization is an atmospheric pressure ionization method for mass spectrometry (MS). Laser light in the UV range is used to ionize molecules in a resonance-enhanced multiphoton ionization (REMPI) process. It is a selective and sensitive ionization method for aromatic and polyaromatic compounds. Atmospheric photoionization is the latest in development of atmospheric ionization methods. The excitation of electrons in atoms and molecules by the absorption of one or more photons can be sufficient for the spatial separation of the electron and the atom or molecule. In the gas phase, this process is called photoionization. The combined energy of the absorbed photons in this process must be above the ionization potential of the atom or molecule. In the simplest case, a single photon has sufficient energy to overcome the ionization potential. This process is therefore called single photon ionization, it is the basic principle of atmospheric pressure photoionization (APPI).For sufficiently high power densities of the incident light also nonlinear absorption processes like the absorption of at least two photons in a rapid sequence via virtual or real states can occur. If the combined energy of the absorbed photons is higher than the ionization potential, this multiphoton absorption process can also lead to ionization of the atom or molecule. This process is called multi-photon ionization (MPI).