Photoelectron Induced Atmospheric Pressure Ionization (PAPI) - a Selective Ionization Method for Molecules with High Electron Affinities

摘要

A new ionization method for analytes with high electron affinity/gas phase acidity based on the photoelectric effect is introduced. Benefits: (1) sensitive: detection limit <= ppbV. (2) selective: outstanding signal-to-noise ratios. (3) fast: real time analysis, no sample preparation necessary. (4) cheap: only PenRay-lamp and modified quartz capillary necessary. (5) easy to handle: no consumables (gases etc.) or adjustments necessary. (6) soft: hardly any fragmentation of the analyte; [M]~(-) or [M-H]~(-) is the dominant signal. Ionization inside the transfer capillary reduces ion transformation processes. Ionization of the analyte without exposure to UV light is possible. Work functions in ambient air are comparable to those at high vacuum. For some metals, the electron yield is highly surface dependent, oxide layers decrease the electron yield by several orders of magnitude. Silver surfaces give relatively constant high electron yields at 254 nm.