Separation of vegetable oil triglycerides by subcritical fluid chromatography with octadecyl packed columns and CO2/modifier mobile phase

The separation of triglycerides (TGs) was studied by subcritical fluid chromatography (SubFC) with octadecyl packed columns and C02/modifier mobile phases. Two detection systems (UV and ELSD) were used. In the first part systematic experiments were carried out for studying the retention behavior of characteristic triglycerides. This was done by analysing a simple vegetable oil (argan), which contains triglycerides differing by the methylene group number (between P and S) or by the unsaturation number (between O, L and Ln). The selectivity calculations from these selected triglycerides have enabled better modeling of the effect of chromatographic parameters on separation (modifier nature and percentage, temperature, and oulet pressure). Following eluotropic strength or specific interaction modifications, polar modifiers (methanol and acetonitrile) improve the selectivity between the selected pairs of triglycerides. An increase in these selectivities also occurs when the temperature decreases, but the effect of pressure on the separation is almost negligible. In a second part, the final optimization was studied. Since polyfunctional octadecyl bonded silica fails to separate one of these pairs, a monofunctional one was chosen. An improved isocratic separation was achieved with seven coupled columns (Hypersil ODS) and with a modifier mixture (ACN/MeOH/CO2). The analysis time was 65 minutes. Applied to complex samples, rapeseed, these conditions enabled separation of numerous compounds in comparison to RPLC.