Atmospheric Pressure Chemical Ionisation

APCI allows for higher flow rates typical of standard HPLC. Typically the mobile phase containing eluting analyte is heated to relatively high temperatures, sprayed with high flow rates of nitrogen and the entire aerosol cloud is subjected to a corona discharge that creates ions. APCI is basically a gas phase ionisation. Solvent compatibility is much wider for APCI as the solvent is evaporated prior to ionisation. APCI is regarded as a less "soft" ionisation technique than ESI, i.e. it generates more fragment ions relative to the parent ion. The predominate ion in an APCI experiment is normally the [M+H]⁺.