High pressure chemical ionization source with coaxial electron entrance and ion extraction apertures

Abstract

A high pressure chemical ionization source operable up to 3 Torr which has good analytical chemical ionization sensitivity (1 x 10/sup -10/ C/..mu..g for methyl sterate) is described. The source has coaxial geometry between electron entrance aperture and ion exit slit, two field shaping rings which lead to parallel equipotential lines over an area of ca. 25 mm/sup 2/ throughout the entire drift region, temperature equillbration of the reactant gas prior to its entry into the reaction by passing it through thermallzing channels in the source block itself, and provisions for cooling and heating to make a temperature range of 175 to 500 K accessible. This source displays characteristics of a drift tube allowing the determination of ion transport properties. Reduced mobilities for He+, Ne+, Ar+, N/sub 2/+, and N/sub 4/+ in their parent gases are within 10% of the accepted literature values. 8 figures, 2 tables.