Analytical glow discharge

Analytical glow discharges have conventionally operated with a constant negative dc potential applied to the cathode. There is no reason, however, that they can t be operated through the application of a pulsed potential, an applied rf potential, or a positive potential applied to the cathode. Many variations have been tried alone and in combination with one another. Perhaps the most interesting among these (because of the unique capabilities that it provides) is the radio-frequency-powered discharge. The analysis of nonconductors is covered extensively in a later chapter, but a brief overview is in order here. 

The four 4s levels play a key role in analytical glow discharges (e.g. for Penning ionization of the sputtered atoms) and they cannot easily be depopulated by radiative decay (due to forbidden transitions for the metastable levels, and to radiation trapping for the resonant levels). Therefore some additional loss processes are incorporated for these levels, in order to describe them with more accuracy ... 

Jakubowski N. and Stuewer D. (1988) Comparison of Ar and Ne as working gases in analytical glow discharge mass spectrometry, Fresenius Z Anal Chem 331 145-149. 

Martin, A., Pereiro, R., Bordel, N., Sanz-Medel, A. (2007) Microsecond pulsed versus direct current glow discharge as ion sources for analytical glow discharge-time of flight mass spectrometry. Journal of Analytical Atomic Spectrometry, 22,1179-1183. 

Many studies have been performed on volatilization by cathodic sputtering in analytical glow discharges used as sources for atomic emission, atomic absorption, and mass spectrometry [152]. Also, studies on the trajectories of the ablated material have been performed, as described, e.g., for a pin glow discharge [153]. 

Figure 7 Mass spectra of a pure Fe sample in argon and in neon (miz 90-100 range). The difference between argon and neon is caused by ArFe+ interferences. Reprinted from Jakubowski N and StUwer D (1989) Comparison of Ar and Ne as working gases in analytical glow discharge mass spectrometry. Fresenius Journal of Analytical Chemistry 355 680-686, with permission of Springer-Verlag, Berlin.

Comparison of Ar and Ne as working gases in analytical glow discharge mass spectrometry,... 

Use of glow-discharge and the related, but geometrically distinct, hoUow-cathode sources involves plasma-induced sputtering and excitation (93). Such sources are commonly employed as sources of resonance-line emission in atomic absorption spectroscopy. The analyte is vaporized in a flame at 2000—3400 K. Absorption of the plasma source light in the flame indicates the presence and amount of specific elements (86). 

In conclusion, GD-OE S is a very versatile analytical technique which is still in a state of rapid technical development. In particular, the introduction of rf sources for non-conductive materials has opened up new areas of application. Further development of more advanced techniques, e. g. pulsed glow discharge operation combined with time-gated detection [4.217], is likely to improve the analytical capabilities of GD-OE S in the near future. 

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

In AFS, the analyte is introduced into an atomiser (flame, plasma, glow discharge, furnace) and excited by monochromatic radiation emitted by a primary source. The latter can be a continuous source (xenon lamp) or a line source (HCL, EDL, or tuned laser). Subsequently, the fluorescence radiation is measured. In the past, AFS has been used for elemental analysis. It has better sensitivity than many atomic absorption techniques, and offers a substantially longer linear range. However, despite these advantages, it has not gained the widespread usage of atomic absorption or emission techniques. The problem in AFS has been to obtain a... 

R.K. Marcus (ed.), Glow Discharge Plasmas in Analytical Spectroscopy, John Wiley Sons, Inc., New York, NY (2002). 

W. W. Harrison, C. M. Barschick, J. A. Khngler, P. H. Ratliff, and Y. Mei. Glow Discharge Techniques in Analytical Chemistry. Anal. Chem., 62(1990) 943A-949A. 

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