Boosted glow discharges for atomic spectroscopy—analytical and fundamental properties

Low pressure glow discharge sources with plane or hollow cathodes are frequently used in spectrochemical analysis, either as sources for optical emission spectroscopy or as primary sources for atomic absorption spectrometry. Increasingly they are also used as ion sources for mass spectrometry. The analytical performances may frequently be improved by “boosting” the intensity of the source by using an auxiliary discharge (dc radio frequency or microwave), by using a magnetic field or by modifying the structure of the source. This review concentrates on sources for optical spectroscopy, discusses the various types of boosted source, the extent to which they have been adopted and the improvement obtained in analytical performance. The amount of work published on the fundamental properties of these sources is limited. Lines of analytical interest increase greatly in intensity; other modifications to the spectra are very complex, but a study of the literature shows that similar changes in the electrical and spectral properties of the source are observed in widely different forms of boosted discharge. These changes are described and some are interpreted in terms of fundamental excitation processes, but much further work will be required before a full understanding of boosted discharges is obtained.