Glow discharge secondary cathodes

This chapter deals exclusively with the methods that have been developed for the direct solids analysis of nonconductive samples by glow discharge mass spectrometry. The basic approaches to operation and sample preparation for the three primary methodologies of compaction, secondary cathode, and radio frequency powering are described. Examples of source performance and practical applications of each are taken from the analytical literature. Whereas this chapter de-... 

Figure 3 Schematic representation (not to scale) of the source assembly used in the secondary cathode approach to glow discharge mass spectrometry (GD-MS) analysis of nonconductive samples. (From Ref. 21.)...

Schelles W., De Gendt S., Muller V. and Van Grieken R. (1995) Evaluation of secondary cathodes for glow discharge mass spectrometry analysis of different nonconducting sample types, Appl Spectrosc 49 939— 944. 

Schelles W. and Van Grieken R. E. (1996) Direct current glow discharge mass spectrometric analysis of macor ceramic using a secondary cathode, Anal Chem 68 3570-3574. 

Fig. 11. Ranges of kinetic energies and densities of species typically present in glow discharge plasmas. A=secondary electrons accelerated through the sheath, B=ions backscattered from cathode (most likely neutralized), C=ions accelerated towards cathode, D=electrons in bulk plasma, E=hot ions and neutrals formed in dissociation reactions (Frank-Condon effect), F=ions in bulk plasma, and G=neutral atoms and molecules. After [39].

Pajo et al. (2001a) used GD-MS to measure impurities in uranium dioxide fuel and showed that these impurities could be used to identify the original source of confiscated, vagabond nuclear materials. De las Heras et al. (2000) used GD-MS to determine neptunium in Irish Sea sediment samples. The sediment samples were compacted into a disk that was used with a tantalum secondary cathode in the glow discharge. Using a doped marine sediment standard for calibration, detection limits down to the mid pg/g level were determined. 

Schelles, W, De Gendt, S., Maes, K., Van Grieken, R.V. (1996) The use of a secondary cathode to analyse solid non-conducting samples with direct current glow discharge mass spectrometry potential and restrictions. Fresenius Journal of Analytical Chemistry, 355, 858-860. 

---