Rapid baseline separation of enantiomers and a mesoform of all-trans-astaxanthin, 13-cis-astaxanthin, adonirubin, and adonixanthin in standards and commercial supplements.

Astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione) is widely used as important colorant in the aquaculture feed industry, and as nutraceuticals in human health products. Synthetic all-trans-astaxanthin consists of a mixture of a pair of enantiomers (3R,3'R and 3S,3'S) and a mesoform (3R,3'S). A high-performance liquid chromatography (HPLC) method for direct, rapid, and baseline separation of three stereoisomers of all-trans-astaxanthin is described for the first time on an immobilized cellulosic column (Chiralpak IC). Enantiomers of two important precursors in the biosynthetic pathway of astaxanthin, adonirubin and adonixanthin, were also directly separated. In addition, the major cis form of astaxanthin (13-cis-astaxanthin) resulted from isomerization was isolated with preparative C18 separation, and the separation of all four stereoisomers of 13-cis-astaxanthin is achieved. Finally, a stereoisomeric purity test of commercial astaxanthin supplements confirmed that they were from a natural source, although their levels were quite low.