Exploring Novel Separation Mechanisms for MOHs Using Supercritical Fluid Chromatography: Preliminary Results

Mineral oil hydrocarbons (MOH) are a complex mixture of hydrocarbons derived from crude oil of petrogenic origin. This complex mixture of isomers is mainly related to two classes of compounds, namely MOSH and MOAH (primarily alkyl-substituted (poly)aromatic hydrocarbons). The conventional analysis couples the use of an HPLC system with GC-FID and often the use of two-dimensional GC (GC×GC) for more detailed elucidation of complex samples.
The selectivity of a silica LC column is exploited to group type separate MOSH from MOAH, and both from the bulk of triglycerides or more polar compounds. Nevertheless, the conventional methods fails to separate naturally occurring interferences, such as terpenes, carotenoids, and olefins in the case of MOAH, hindering a correct quantification of this fraction in some samples. Supercritical fluid chromatography (SFC) has been thus explored to evaluate possible alternative selectivities to separate MOSH and MOAH from the naturally occurring interferences. The elution behaviour of different columns was investigated by SFC-PDA using a motor oil. The detectability of MOH in PDA is limited, but different profiles could be detected, leading to the interest in a more detailed investigation. The different elution fractions were collected and are now under characterization by GC×GC-ToFMS/FID to understand the elution behaviour.
Preliminary results obtained on a Pyrenylethyl (PyE) column are shown, showing a peculiar elution mechanism compared to what is usually obtained using a silica column in LC. Further investigation will be performed to optimize the separation of MOSH and MOAH first and then from the interferences.