using ASG 2901 GC×GC-FID

Paraffinic middle distillates such as hydrogenated vegetable oil (HVO) or synthetic fuels from Fischer-Tropsch processes (XtL) differ significantly from conventional middle distillates in their composition. They are characterized in particular by the low content of aromatic compounds. According to the specification standard DIN EN 15940, the total aromatics content is limited to a maximum of 1.1 %(m/m). As a rule, however, the content is significantly lower. 

Established methods, such as analysis by HPLC with RI or UV detection, can fail to achieve reliable results in this concentration range. An ideal alternative was provided by analysis using comprehensive two-dimensional gas chromatography (GC×GC) with subsequent detection by FID. Information on how GC×GC works can be found in the info letter 01/2019.

This technique is used, among other things, to separate complex petrochemical samples. In principle, substances that have the same boiling point but different polarities can be separated from each other along the second dimension. The thus increased selectivity and higher sensitivity, allows to reliably quantify even low concentrations of total aromatics down to 0.05% (m/m). The standard price of an analysis is 250,00 €.

The following graphic shows a two-dimensional chromatogram of an XtL fuel.

For the separation, a reversed-phase combination was used here with a 50% phenyl-substituted column in the first dimension and a 100% polydimethylsiloxane column in the second dimension. The peaks of the homologous series of n-alkanes are easy to identify.