Using supercritical fluid chromatography to determine diffusion coefficients of lipids in supercritical CO2

Supercritical fluid chromatography was used for the determination of diffus ion coefficients by the Taylor-Aris peak broadening technique. Binary diffu sion coefficients of pure lipids, such as fatty acids and their esters, tri glycerides and a diglyceride in supercritical carbon dioxide, were determin ed and the effect of pressure (25.0-36.0 MPa), temperature (40-60 degrees C ) and number and position of double bonds on the diffusion coefficient was studied. Addition of a secondary solvent such as ethanol indicated an appar ent enhancement in the diffusion coefficient of oleic acid. Diffusivity of oleic acid decreased with pressure and increased with temperature. Increasi ng the number of double bonds reduced the diffusion coefficient of fatty ac ids. A shift in the position of double bond from omega-3 to omega-6 resulte d in an increase in the diffusion coefficient of linolenic acid. The diffus ion coefficient of methyl oleate was higher than that of ethyl oleate, indi cating an alkyl effect in the esters of fatty acids. Diffusion coefficients of free fatty acids were lower than those of their eaters. Knowledge of tr ansport properties such as diffusion coefficients in supercritical fluids i s of great importance to the design of extraction, fractionation and reacti on systems involving lipids using these media. (C) 2000 Elsevier Science B. V. All rights reserved.