Separation of diastereomers, i.e., S,S, S,R, R,S, and R,R on a conventional normal or reverse phase column was not possible due to the large distance of both chiral centers . For this reason, chromatography on a chiral column (two columns connected in series) was used to separate standards and real samples. A phospholipid with hydroxyl groups, such as PG, easily reacts with 3,5-dinitrophenyl isocyanate to form the corresponding urethane derivatives that are separable in chiral columns.