Thereby the mixture of materials, which has to be investigated, is injected into a fine capillary column by an injector. This column is out of a material similar to glass and inside coated with chemical modified polysiloxane.
The capillary column has a length of 15 m and an inner diameter of 0.25 mm. The polysiloxane layer has a thickness of only 0.25 µm. The column is mounted in a thermal adjustable oven. Hydrogen is permanent flowing through the column as carrier gas. As soon as the used engine oil gets into the column, it becomes vaporized and it`s single components are carried from the carrier gas trough the column. Depending to their structure and the oven temperature the single components are vaporizing with different speed. Therefore their resistance time at the surface of the column is different and they are going to be split according to their boiling temperature. A detector registers the single components, when they leave the column. The detector draws the single elements into a diagram. As later a component comes to the exit of the column, as higher the boiling temperature is. The area below a peak from the Gas-phase chromatograph is proportional to the amount of the component in the mixture.
It`s also possible to find the comparatively difficult ignitable “biodiesel” as fuel in the motor oil.
If there is too much fuel in the motor oil, it becomes too weak to build up a stable lubrication film.