Discharge corona, beam source

The APCI interface uses a heated nebulizer to form a fine spray of the HPLC eluate, which is much finer than the particle beam system but similar to that formed during thermospray. A cross-flow of heated nitrogen gas is used to facilitate the evaporation of solvent from the droplets. The resulting gas-phase sample molecules are ionized by collisions with solvent ions, which are formed by a corona discharge in the atmospheric pressure chamber. Molecular ions, M+ or M , and/or protonated or de-protonated molecules can be formed. The relative abundance of each type of ion depends upon the sample itself, the HPLC solvent, and the ion source parameters. Next, ions are drawn into the mass spectrometer analyzer for measurement through a narrow opening or skimmer, which helps the vacuum pumps to maintain very low pressure inside the analyzer while the APCI source remains at atmospheric pressure. 

The formation of molecular beams from nozzles of various shapes has been reported." Campargue ° recommends a short straight capillary with aratio of length to diameter equal to or greater than 2. In our homemade ion source, a 0.3-mm-diameter hole in a flat 1.0-mm-thick stainless-steel disk protected by a gas curtain has proven to be very robust and reliable in experiments with corona discharge ionization and electrospray. 

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