Thermal ionization

When these isotope ratios are measured by TIMS, mass-dependent fractionation occurs as species are emitted by the hot filament.

Fractionation occurs due to the excitation of the sample and therefore must be corrected for accurate measurement of the isotope ratio.

It requires a stable power supply, and is suitable for species with a low ionization energy, such as strontium and lead.

The hot filament reaches a temperature of less than 2,500 °C (2,770 K; 4,530 °F), leading to the inability to create atomic ions of species with a high ionization energy, such as osmium and tungsten.

Although the TIMS method can create molecular ions instead in this case, species with high ionization energy can be analyzed more effectively with MC-ICP-MS.[citation needed]

Surface ionization effect in a vaporized cesium atom at 1500 K, calculated using a grand canonical ensemble . Y-axis: average number of electrons on the atom; the atom is neutral when it has 55 electrons. X-axis: energy variable (equal to the surface work function ) dependent on electron chemical potential μ and electrostatic potential ϕ .