LASER ENHANCED IONIZATION SPECTROMETRY IN ANALYTICAL FLAMES

A new variety of analytical atomic flame spectrometry called laser enhanced ionization (LEI) has been developed. The method relies on the enhanced rate of thermal ionization of the analyte element following photoexcitation with a dye laser tuned to an appropriate transition wavelength. This enhanced ionization rate can be electrically measured directly in the flame, and therefore no optical detection system is required. Detection limits have been measured for 18 elements, showing order-of-magnitude superiority over other flame based spectroscopic methods in many cases. A variety of types of transitions have been successfully utilized, including ground state transitions, thermally excited state transitions, low transition probability transitions, and a two-photon transition. The strong dependence of LEI sensitivity on the ionization potential of the analyte element and the energy of the laser populated excited state is discussed. Other topics discussed include interference problems encountered and the application of LEI to the analysis of real samples. © 1979, American Chemical Society. All rights reserved.