Atmospheric pressure photoionisation: An ionization method for liquid chromatography-mass spectrometry

Atmospheric pressure photoionization (APPI) has been successfully demonstra ted to provide high sensitivity to LC-MS analysis. A vacuum-ultraviolet lam p designed for photoionization detection in gas chromatography is used as a source of 10-eV photons. The mixture of samples and solvent eluting from a n HPLC is fully evaporated prior to introduction into the photoionization r egion. In the new method, large quantities of an ionizable dopant are added to the vapor generated from the LC eluant, allowing for a great abundance of dopant photoions to be produced. Because the ion source is at atmospheri c pressure, and the collision rate is high, the dopant photoions react to c ompletion with solvent and analyte molecules present in the ion source. Usi ng APPI, at an LC flow rate of 200 mu L/min, it is possible to obtain analy te signal intensities 8 times as high as those obtainable with a commercial ly available corona discharge-atmospheric pressure chemical ionization sour ce.