* Thermal desorption: the adsorbent material is flash-heated so that all adsorbed VOCs are carried away from the adsorbent and injected into the separation system. This is how work injectors in gas chromatography machines, which literally volatilize introduced samples. For VOCs adsorbed on bigger amount of adsorbent material such as  cartridges, thermal desorption may require the use of a specific machine, a thermal desorber, connected to the separation system.
* Desorption by solvent: VOCs adsorbed on the adsorbent material are carried away by a small quantity of solvent which is volatilized and injected in the separation system. Most commonly used solvents are very volatile molecules, such as methanol, to avoid co-elution with slightly heavier VOCs