Triacylglycerol analysis of partially hydrogenated vegetable oils by silver ion HPLC

Abstract

A fast and reliable method was developed for the analysis of positional and geometrical triacylglycerol isomers in partially hydrogenated vegetable oils. A binary gradient of heptane/acetonitrile was employed in silver ion HPLC with evaporative light scattering detection. Good resolution of native and partially hardened oils was achieved within 22 min for palm oil and within 60 min for rapeseed oil. Initial stability problems were found to be caused by decreasing acetonitrile concentration in the solvent mixture, due to selective evaporation of acetonitrile. By tightening the bottle caps and plugging the usual ventilation inlets, this could be prevented; the system then became very stable. A complementary system (heptane/acetone) was used to confirm the absence of 1,2‐Elaidin‐3‐palmitin in the hydrogenated samples. This system shows better resolution in the more saturated region (up to three double bonds). However, for less saturated species, peak‐split problems occurred (e.g. for triolein), and the elution strength of acetone was not sufficient for the elution of the most polyunsaturated triacylglycerols of rapeseed oil. This would have required a ternary gradient with an additional, stronger solvent, e.g. acetonitrile. Hence, the original heptane/acetonitrile system was retained as the method of choice. It is sufficiently fast and accurate over a wide range of unsaturation to make it suitable for hydrogenation process control, especially of continuous processes with rapidly changing product composition.

Stationary phases for silver ion chromatography of lipids: Preparation and properties

“…Application of Ag-HPLC to the separation of FA derivatives, TAG, and complex lipids has been presented in several comprehensive reviews [18,19,90,94,95]. Recently special attention has been attracted by (i) the separation of positionally isomeric unsaturated FA [95] with special emphasis on conjugated dienes (usually denoted as CLA, see [96] and the literature cited therein) and (ii) the regioselective separation of TAG with special emphasis on structured species (see, for example, [92]).…”