Editing Chemical ionization (section)

===Atmospheric-pressure chemical ionization===
Chemical ionization in an atmospheric pressure electric discharge is called [[atmospheric pressure chemical ionization]] (APCI), which usually uses water as the reagent gas. An APCI source is composed of a [[Liquid chromatography–mass spectrometry|liquid chromatography]] outlet, nebulizing the eluent, a heated vaporizer tube, a corona discharge needle and a pinhole entrance to 10<sup>−3</sup> torr vacuum.<ref name=":3" /> The analyte is a gas or liquid spray and ionization is accomplished using an atmospheric pressure corona discharge. This ionization method is often coupled with high performance liquid chromatography where the mobile phase containing eluting analyte sprayed with high flow rates of [[nitrogen]] or [[helium]] and the aerosol spray is subjected to a corona discharge to create ions. It is applicable to relatively less polar and thermally less stable compounds. The difference between APCI and CI is that APCI functions under atmospheric pressure, where the frequency of collisions is higher. This enables the improvement in sensitivity and ionization efficiency.<ref name=":1" />