Analysis of sterol esters from alga and yeast by high-performance liquid chromatography and capillary gas chromatography-mass spectrometry with chemical ionization.

Sterol esters from the green alga Chlorella kessleri and the yeast Saccharomyces cerevisiae were analysed by tandem high-performance liquid chromatography (HPLC-HPLC). Non-polar lipids were separated by normal-phase HPLC into individual classes and the fraction of sterol esters was subsequently separated by reversed-phase HPLC into intact molecular species. Further separation and identification of the fractions after HPLC were effected by capillary gas chromatography-mass spectrometry (cGC-MS) with positive and/or negative chemical ionization. A technique consisting of direct injection of the sample after its passage through the detector into the on-column injector of the gas chromatograph was used to transfer the sample from HPLC-HPLC to cGC-MS. By means of this method it was possible to demonstrate more than 30 sterols in both the alga and the yeast, and more than 20 new sterol esters were detected.