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- Research Support Building (CACTUS)
- Rúa de Constantino Candeira, 1. Campus Vida , 15782Santiago de Compostela
- Phones
- 881 816 242
These photons do not have sufficient energy to ionise background molecules such as oxygen, nitrogen or common HPLC/UHPLC solvents. The ionisation process is controlled by the energy of the incident photons (hν) and the ionisation energy of the analyte, hence the name of the technique.
The APPI mechanism, in positive mode, can be of two forms:
- Direct APPI: takes place when the energy of the incident photons is higher than the ionisation energy of the analyte (A), making direct photoexcitation possible.
The same ionisation is also possible in the presence of solvent molecules (M) through proton extraction.
Photodissociation, radioactive decay and collisional quenching can also take place. The APPI technique is not restricted to the positive ionisation mode; negative ions can be produced through charge transfer in secondary ion reactions.
- APPI with dopant: A dopant (toluene, benzene, acetone...) whose ionisation energy is lower than the energy of the incident photons can be used, generating D+. In this way, the analytes are ionised by proton or electron transfer.
In the presence of protic solvents, the dopant often produces [A+H]+ ions, these being essentially predominant.
Like ESI and APCI, it is compatible with LC separation techniques; it also produces little fragmentation. APPI is a technique for thermally stable non-polar analytes that have difficulty ionising in ESI or APCI, such as polycyclic aromatic hydrocarbons (PAHs). In fact, analytes containing benzene rings or conjugated double bonds are suitable samples to be photoionised with this technique and have the advantage of having a relatively low susceptibility to ion suppression and matrix effect.
Mass Spectrometry and Proteomics Unit
- Research Support Building (CACTUS)
- Rúa de Constantino Candeira, 1. Campus Vida , 15782Santiago de Compostela
- 881 816 242