Simultaneous separation of sixteen positional and optical isomers of the tryptophan family by ligand-exchange micellar electrokinetic chromatography

Ligand-exchange micellar electrokinetic chromatography has been used for the simultaneous separation of 16 positional and optical isomers of the tryptophan family. The Cu(II) complex with L-hydroxyproline was used as the chiral selector. Two groups of anionic surfactant,linear alkylbenzenesulfonates (LAS) and straight-chain alkyl sulfates such as sodium n-decyl sulfate (SDeS), sodium dodecyl sulfate (SDS) and sodium n-tetradecyl sulfate (STS), were used for simultaneous separation. The best result was obtained by use of SDS. The influence of SDS concentration and of pH on the separation was investigated. The separation behavior in the absence of the Cu(II) complex with L-hydroxyproline was also examined. Use of organic modifiers causes the resolution to decrease. Relationships between the logarithm of the octanol-water partition coefficient (log P-OW) and resolution, and between log P-OW and migration time are discussed.