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

Abstract

SummaryThe separation of triglycerides (TGs) was studied by subcritical fluid chromatography (SubFC) with octadecyl packed columns and C02/modifier mobile phases. Two detection systems (UVand 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.

Overview of the retention in subcritical fluid chromatography with varied polarity stationary phases

“…Figure 4 presents the separation of a rapeseed oil composed of numerous TGs using a column length of 120 cm [34]. The retention rule is close to that observed in nonaqueous RP LC (NARP-LC) with ODS stationary phases, i. e. retention follows the partition number PN.…”

Plant Metabolites and Nutritional Quality of Vegetables

“…Compared with HPLC, SFC provides rapid separations without the use of organic solvents. SFC has been applied to the separation of vegetable carotenoids and carotenoid isomers (Schmitz and others 1989), and the isolation of vegetable lipids, tocopherols, and carotenoids (Señoráns and others 1999; Lesellier and Tchapla 2000; Ollanketo and others 2001). Due to lack of toxicity, the method has been extended to supercritical fluid extraction (SFE) of plant nonpolar substances such as essential oils, flavor and fragrance compounds, lipids, carotenes, and alkaloids (Jarvis and Morgan 1997).…”

Supercritical Fluid Chromatography – Theoretical Background and Applications on Natural Products

“…On these stationary phases, coelutions occur frequently, so that a combination with MS might be required. Reversed-phase materials are a more selective option when using packed columns, either with UV-, ELSD, or MS detection [73][74][75]; the described separation conditions were typical for SFC. Lesselier et al investigated the influence of different polar modifiers and obtained the best results with acetonitrile.…”

“…An increase in selectivity was noticed when decreasing the temperature from 30 to 5°C. On the other hand, pressure changes had no big impact on selectivity [73]. A less common approach is the use of SIC in combination with SFC [76].…”