Simulated distillation, GC

Chromatographic procedures are used to break complex mixtures of substances down into their components.

In gas chromatography, the mixture for investigation is injected into a narrow capillary column using an injector. 

The column is placed in a thermally adjustable oven. Hydrogen, as a carrier gas, is flowed through it continuously. If the sample enters the column, it evaporates and the individual components are flushed through the column in gaseous form by the carrier gas.

Depending on their structure and the temperature in the oven chamber, the individual components remain on the surface of the column for different lengths of time. They are therefore broken down based on their boiling temperature. As the individual components leave the column, a detector identifies them. It records them in a chromatogram.

The later a component is detected at the column outlet, the higher its boiling point. The area under a peak in the chromatogram is proportionate to the amount of the component in the mixture.

For diesel fuel, conclusions can be drawn regarding the boiling process, initial boiling point, the amount of steam in %(V/V) at 250 °C and 350 °C, the temperature at which 95% (V/V) has evaporated, and the final boiling point. Biodiesel content and other mixtures can also be determined.

In oils, this method also enables the detection of mixtures (e.g. vegetable oil in engine oils) or short-chain, more volatile products of cracking in heat transfer oils. Yet for the other uses, questions always come up that can be answered with the help of the boiling profile.