Class separation of lipids and polycyclic aromatic hydrocarbons in normal phase high performance liquid chromatography – A prospect for analysis of aromatics in edible vegetable oils and biodiesel exhaust particulates

• We investigated the retention characteristics of lipids and PAHs on five stationary phases.
• The goal was to optimize sample cleanup of PAHs in lipid matrices by HPLC–GC–MS system.
• A structure–retention model based on PLS was made to find a rationale for retention mechanisms.
• The optimal condition was evaluated by analysis of an extract and a spiked reference material.

The retention characteristics of the major lipid components in biodiesels and edible oils as well as representative polycyclic aromatic compounds (PAHs) have been investigated on five different normal phase HPLC stationary phases, in order to optimize class separation for an automatized online HPLC cleanup of PAHs prior GC–MS analysis. By stepwise comparison of different hexane/MTBE compositions as mobile phases on cyano-, phenyl-, pentabromobenzyl-, nitrophenyl- and amino-modified silica columns, the capacity and selectivity factors for each analyte and column could be calculated. It was concluded that the most suitable column for backflush isolation of PAHs in biodiesel and edible oil matrices was the pentabromobenzyl-modified silica (PBB). A previously described online HPLC–GC–MS system using the PBB column was then evaluated by qualitative and quantitative analysis of a biodiesel exhaust particulate extract and a vegetable oil reference material. The GC–MS full scan analysis of the biodiesel particulate extract showed that the lipids had been removed from the sample and a fraction containing PAHs and oxygenated derivatives thereof had been isolated. Quantified mass fractions of PAHs of the reference material BCR-458 agreed well for most of the certified PAH mass fractions in the spiked coconut oil reference material.