Glow-discharge sampling with spectrometries

Applications of glow-discharge sampling in combination with spectrometries... 

S. DeGendt, R.E. Van Grieken, S.K. Ohorodnik and W.W. Harrison, Parameter evaluation for the analysis of oxide-based samples with radio frequency glow discharge mass spectrometry, Anal. Chem., 67 (1995) 1026-1033. 

For analysis of solutions, ICP-mass spectrometry (ICP-MS) is very promising (Houk et al., 1980 Houk, 1986 Bacon et al., 1990). Recent advances in separation and preconcentration techniques are discussed by Horvath et al. (1991). Bacon et al. (1990) report that although ICP-MS is a multi-element technique, recent papers tend to concentrate on a small number of target elements. With isotope dilution mass spectrometry (IDMS), detection limits are further reduced (Heumann, 1988) IDMS is also suitable for accurate speciation in very low concentration levels of elements (Heumann, 1990). For the direct analysis of solid samples, glow discharge mass spectrometry (GD-MS) (Harrison etal., 1986) is of interest. Tolg (1988) has suggested that a substantial improvement in the absolute detection power of GD-MS, as applied to micro analysis, can be expected, at least in comparison with the ICP as ion source. 

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-... 

Many other types of atomization devices have been used in atomic spectroscopy. Gas discharges operated at reduced pressure have been investigated as sources of atomic emission and as ion sources for mass spectrometry. The glow discharge is generated between two planar electrodes in a cylindrical glass tube filled with gas to a pressure of a few torr. High-powered lasers have been employed to ablate samples and to cause laser-induced breakdown. In the latter technique, dielectric breakdown of a gas occurs at the laser focal point. 

Fig. 12. Amplitude noise spectra for a matrix line in glow discharge source (GDS) atomic emission spectrometry. Steel standard sample 218A (Research Institute CKD, Czech Republic) / 50 mA argon pressure 600 Pa burning voltage 900 V 0.35 m McPherson monochromator line Fe I 371.9 nm. (a) Without needle valve between the vacumm pump and the GDS, (b) with needle valve between the pump and the GDS. (Reprinted with permission from Ref. [40].)...

As the sample volatilization is due to cathodic sputtering only, matrix interferences as a result of the thermochemical properties of the elements do not occur. This has been shown impressively in early comparative studies of glow discharge atomic spectrometry and spark emission spectrometry with aluminum samples (Fig. 107) [480]. It must be stated, however, that with advanced sparks, where through the use of fiber optics only those parts of the spark plasma are observed that are not involved in sample ablation, matrix interferences in the case of spark emission spectrometry are also lower. The analysis of similar alloys with different metallographic structures by glow discharge atomic spectrometry can often be carried out with one calibration. 

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