IONIZATION METHODS IN MASS SPECTROMETRY
In the JEOL Lcmate, components for the APCI method are standard equipment. Components for the ESI method and the FAB and FritFAB ionization are optional.
In the APCI method, the sample solution is vaporized under atmospheric pressure and ionized by corona discharge.
APCI is a chemical-ionization technique which uses gas-phase ion-molecule reactions at atmospheric pressure. Primary ions are produced by corona discharge on a solvent spray. The chromatographic eluate ( from 0.1 to 1 ml/min) is directly introduced into a pneumatic nebulizer, where it is converted into a thin fog by a high speed air or nitrogen beam. Droplets are then displaced by the gas flow through a carefully controlled heated quartz tube , known as a desolvation/vaporization chamber. The hot gas (120°C) and the compounds leaving this tube and arriving at the reaction area of the source are chemically ionized (under atmospheric pressure) via proton transfer. The evaporated mobile phase acts as the ionising gas and yields (M+H)+ ions. The electrons needed for primary ionization result from corona discharge or negatron emitters. Thermal decomposition is kept to a minimum and ionization of the substrate is very efficient. Differential pumping over several several stages separated by skimmers, maintains a good vacuum and allows entry of as many as ions as possible to the analyzer.
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