Retention behavior of triglycerides in subcritical fluid chromatography with carbon dioxide mobile phase

The retention behavior of triglycerides (TGs) was studied in subcritical fluid chromatography (SubFC) at 150 atm and in the temperature range of 0 to 25°C using an octadecyl-silica (ODS) column and carbon dioxide as the mobile phase without modifier. Both the retention and selectivity drastically changed with temperature. The contributions of the carbon number and the number of double bonds to the retention were similar to those in reversed-phase liquid chromatography with ODS column, which means that the concept of equivalent carbon number (ECN) can be applied to SubFC. In addition, ECN was expressed as a function of temperature, so that the retention of TGs can be predicted at any temperature. Predicted retentions based on five standard TGs were in good agreement with experimental ones within 2.1% error. Hold-up time was also correlated to the column temperature, so that simulated chromatograms can be produced. This method can be used to optimize the separation of various plant oils. Moreover, separations at different temperatures allowed us to identify each TG in oils.