Thermal surface ionization source double filament

Figure 2.26 a) Experimental arrangement of a single-filament thermal surface ionization source b) Schematic diagram of a double-filament arrangement for thermal surface ionization. (H. Kienitz (ed.), Massenspektrometric (1968), Verlag Chemie, Weinheim. Reproduced by permission of Wiley-VCH.)... 

Single, double and triple filaments have been broadly used in thermal ionization sources. In a single filament source, the evaporation and ionization process of the sample are carried out on the same filament surface. Using a double filament source, the sample is placed on one filament used for the evaporation while the second filament is left free for ionization. In this way, it is possible to set the sample evaporation rate and ionization temperature independently, thus separating the evaporation from the ionization process. This is interesting when the vapour pressure of the studied elements reaches high values before a suitable ionization temperature can be achieved. A triple filament source can be useful to obtain a direct comparison of two different samples under the same source conditions. 

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