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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.

Additional recommended knowledge

Recognize and detect the effects of electrostatic charges on your balance

Weighing the right way

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]

$\frac{Y_1}{Y_0} = \frac{g_1}{g_0} \exp \Bigg(\frac{\phi-IP}{kT}\Bigg)$

$\frac{Y_1}{Y_0}$ = ion to neutral ratio

$\frac{g_1}{g_0}$ = statistical weights of ion and neutral states

φ

= surface work function

IP = element ionization potential

k = Boltzmann's constant

T = surface temperature

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

^ 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 on 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. PMID 8049033.