The present disclosure is related to the six isomer structures (OBI-821-1990-V1A, OBI-821-1990-V1B, OBI-821-1990-V2A, OBI-821-1990-V2B, OBI-821-1858-A, and OBI-821-1858-B) of isolated OBI-821 adjuvant and the method for evaluating the quality thereof. The method of the present disclosure adopts hydrophilic interaction liquid chromatography (HILIC) and reverse phase high performance liquid chromatography (RP-HPLC) either alone or in tandem and is able to separate the isomers of OBI-821 adjuvant in the consequent chromatography. Accordingly, the quality of OBI-821 adjuvant can be further evaluated.