Advantages of total lipid hydrogenation prior to lipid class determination on chromarods-SIII

The changes in detector responses of lipid classes for standards and natural lipid samples after hydrogenation were investigated with the TLC/FID Iatroscan system using Chromarods-SIII (Newman-Howells Associates, Ltd., Midwales, U.K.). Samples included lipids of human plasma and erythrocytes, egg lipids, a fish oil concentrate and triacylglycerols of sea scallop, as well as standards (mono-, di- and triacylglycerols, phosphatidylcholines, phosphatidylethanolamines, lysophosphatidylcholines, free fatty acid, and sterol). The duration of hydrogenation was increased from 45 min to 90 min for some samples to bring hydrogenation to completion. Since the detector response of a lipid class is known to depend on its relative position on the Chromarod, different solvent systems which would vary the migration rate were investigated. The increases in response after hydrogenation, given as relative percent increase (RI), were significant for all compounds examined (p<0.05), and ranged from 7 to 45%. Among the triacylglycerols, the fish oil and the sea scallop triacylglycerols with wide ranges of fatty acid composition had the highest RI while the other lipid classes did not differ from each other. Differences in the solvent systems did not affect the RI except for fish oil triacylglycerols. The precision of peak area measurements was usually better after hydrogenation. The combination of greater sample stability, greater response, improved resolution, and simpler choice of standards make hydrogenation a significant advance in TLC/FID quantification.