Atmospheric-pressure chemical ionization

Atmospheric pressure chemical ionization (APCI) is an ionization method used in mass spectrometry (commonly LC-MS) which utilizes gas-phase ion-molecule reactions at atmospheric pressure. It is an ionization method that is similar to chemical ionization (commonly used in GC-MS) where corona discharges on a solvent spray produce primary ions. APCI is mainly used with polar and relatively nonpolar compounds with a molecular weight of less than 1500 Da, generally giving monocharged ions. Because of its ability to run in sequence with HPLC, it has gained a large popularity in trace analysis detection and pharmacology.