Townsend discharge

Figure 10. Corona (or Townsend) discharge in nitrogen containing 1 X 10 2 mole % of water vapor...

The disadvantage of the fluid model is that no kinetic information is obtained. Also, transport (diffusion, mobility) and rate coefficients (ionization, attachment) are needed, which can only be obtained from experiments or from kinetic calculations in simpler settings (e.g. Townsend discharges). Experimental data on... 

FIG. 25. Simulation results for quasi-Townsend discharges (a) ionization coefficients for SiHa, H2, and Ar (b) attachment coefficients for SiHa and CFa-... 

P.J. Arpino, J.P. Bounine, M. Dedieu, G. Guiochon, Optimization of the instrumental parameters of a combined LC-MS, coupled by an interface for DLL IV. A new desolvation chamber for droplet focusing or townsend discharge ionization, J. Chromatogr., 271 (1983)43. 

In Townsend discharges, free electrons ionise the gas molecules. Several processes for gas ionisation are known. Table 2.1 lists the most important ones. The ionisation of a neutral gas molecule A takes place if the kinetic energy of the electron e is greater than the ionisation potential Vt of the gas molecule (see Table 2.2) ... 

Let us now discuss whether electrochemical discharges could be Townsend discharges. Electrochemical discharges take place through a gas film formed... 

For electrochemical discharges produced at an anode, the situation is more complex and is discussed later in the chapter. As will be discussed, chemical and electrochemical reactions taking place in the gas film play an important role and are responsible for the formation of hydrogen and the behaviours similar to arc and Townsend discharges observed by Morse. 

Ionization by collision of pairs of excited helium atoms was first proposed by Schade on the basis of observations of the pressure dependence of additional ionization that was in excess of that due to avalanche electrons in a Townsend discharge. Further studies by Schade " and Buttner confirmed the original observations " and lead to the conclusion that the reaction... 

It is possible to include a Townsend discharge or a filament and a repeller electrode to allow plasma chemical ionization to be performed. For some compounds, the sensitivity, selectivity, and fragmentation behavior can be modified. The advantage of the technique is the simplicity of transferring previou.sly developed LC procedures since the normal flow rales and some of the common buffers (e.g., ammonium acetate, formate) can be used. 

McAfee, K. B., fr., Edelson, D. (1963) Identification and mobility of ions in a townsend discharge by time-resolved mass spectrometry, Proc Phys Soc Land, 81, 382-384. 

Meuldermans et al. [12] presented a complete study on the metabolic pathways of SUF and ALF from the excreta of rats and dogs. Among other techniques, they used GC MS in El and PCI modes for the characterization of major metabo lites after derivatization by silylation or acylation. The same laboratory [13] has identified the two major metabolites of ALF in human urine. Lavrijsen et al. [14] have studied the biotransformation of SUF in vitro in different species using GC-MS in El mode, but also with desorption Cl and Townsend discharge ionization. Several metabolites were identified unambiguously on the basis of their MS data, in comparison with the mass spectra of authentic reference compounds. 

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