Abstract

Common mass spectrometry utilizing non-selective ionizationprocesses, like electron bombardment, has an excellent isotopic selectivity, but is unable to distinguish different isobars. For example, the ⁹⁰Sr signal would interfere with the ⁹⁰Rb signal in a mass spectrometer based on electron impact ionization. The introduction of tuneable dyelasers in the mid 70's made it possible to selectively excite and/or ionize free atoms. A method based on resonance excitation of atoms, laser enhanced ionization (LEI), have been developed and used for trace element analysis in flames (1) and recently also in atmospheric pressure graphite furnaces (2). Sensitivities in the ppb and even in the subppb range have been reported for many elements. The selective excitation of the atoms eliminate the isobaric interferences confronted in mass spectrometry, but unless a very narrow band-width laser is used, the method will suffer from an unability of distinguishing different isotopes. For example ⁹⁰Sr can not be distinguished from ⁹¹Sr or ⁹²Sr in LEI.

© 1990 Optical Society of America