The identification of dipalmityl zeaxanthin as the major carotenoid in Gou Qi Zi by high pressure liquid chromatography and mass spectrometry

The carotenoid in Gou Qi Zi was extracted by hexane, followed by repeated chromatography on a silica column. The major carotenoid recovered from the chromatographic step was subjected to hydrolysis in potassium hydroxide (KOH). The hydrolytic products were separated on a silica column followed by analysis for their molecular sizes by a Micromass Platform LCZ. The retention time of the carotenoid in Gou Qi Zi is 2.3 min. Upon hydrolysis, new carotenoid peaks appeared. The molecular ions detected by APCI^- of the carotenoid at 2.3, 6.8 and 28 min are 1044, 806 and 568, respectively. The molecular sizes matched to that of dipalmityl zeaxanthin, monopalmityl zeaxanthin and zeaxanthin, respectively. The monopalmityl zeaxanthin peak appeared first and faded away as the free zeaxanthin peak reached the maximal size.