Thermal ionization
In thermal ionization, also referred to as surface ionization, chemically-purified material loaded onto a filament which is then heated to cause some of the material to be ionized as it boils off the hot filament. Filaments are generally flat pieces of metal around 1-2mm wide, 0.1mm thick, bent into an upside-down U shape and welded to steel posts that supply a current.
Saha-Langmuir equation
Saha-Langmuir equation
The likelihood of ionisation is a function of the filament temperature, the work function of the filament substrate and the ionization energy of the element.
This is summarised in the Saha–Langmuir equation:[1]
- <math>\frac{Y_1}{Y_0} = \frac{g_1}{g_0} \exp \Bigg(\frac{\phi-IP}{kT}\Bigg)</math>
- <math>\frac{Y_1}{Y_0}</math> = ion to neutral ratio
- <math>\frac{g_1}{g_0}</math> = statistical weights of ion and neutral states
- <math>\phi</math> = surface work function
- IP = element ionization potential
- T = surface temperature
Thermal ionization mass spectrometry
Thermal ionization mass spectrometry
One application of thermal ionization is thermal ionization mass spectrometry (TIMS). The ions being produced at the filament are directed into a mass spectrometer to analyze the elements or isotopes present in the sample.[2]
References
References
- ↑ Dresser, M. J. (January 1968). “The Saha-Langmuir Equation and its Application” (PDF). Journal of Applied Physics. 39 (1): 338–339. doi:10.1063/1.1655755. Retrieved 2007-10-11.
- ↑ Aggarwal SK, Kinter M, Fitzgerald RL, Herold DA (1994). “Mass spectrometry of trace elements in biological samples”. Critical reviews in clinical laboratory sciences. 31 (1): 35–87. doi:10.3109/10408369409084673. PMID 8049033.
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