Use of relationships between retention behaviors and chemical structures in subcritical fluid chromatography with CO2/modifier mixtures for the identification of triglycerides

Satisfactory separations of vegetable oil triglycerides (TG) differing in f atty acid composition are obtained by subcritical fluid chromatography (Sub FC) with octadecyl packed columns and CO2/modifier mobile phases, However, the identification of TG can be sometimes difficult due to the small retent ion differences between the compounds. A method of TG identification in Sub FC was achieved, which does not require calculation of retention pattern bu t uses the differences in retention behavior related to TG structure and to the nature of the subcritical mobile phases. These retention differences w ere produced by the variation of either outlet pressure or modifier percent age or of temperature. Whatever the column aging, this method allows the de termination of the triglyceride total chain length and double bond number. Among numerous structures, these two criteria restrict the structural hypot hesis at worst to three or four possibilities and sometimes only to one. Th e validity of this relative identification method was confirmed by electron ic impact mass spectrometry of triglyceride fractions collected from the an alysis of a peanut oil. The analysis of concentrated fractions is favored b y the spontaneous elimination after the pressure regulator of carbon dioxid e, the main fluid of the subcritical mobile phase.