CHIRAL CHROMATOGRAPHY OF AMINO-ACIDS AND HYDROXY-ACIDS ON SURFACE-MODIFIED POROUS GRAPHITE

A new type of chiral stationary phase has been prepared by coating por ous graphite with a near-monolayer of an adsorbed enantiomeric modifie r which then acts as an adsorbed stationary phase. The most effective modifiers are L- or D-isomers of N-(2-naphthalene-sulphonyl)-phenylala nine (NS-Phe). Conveniently 80% of monolayer coverages, corresponding to 1.2 mu mol m(-2), are achieved by adsorption of NS-Phe from methano lic solution. Enantiomeric separations by complexation with cupric ion shaw base-line resolution of alpha-amino and alpha-hydroxy acids with separation factors up to 2. Identical separations are achieved with c hiral phases made from the L- and D-isomers of NS-Phe except that the elution orders of enantiomers are inverted. Reduced plate heights are around 5 and the adsorbed chiral phases are extremely stable, retentio n ratios being unchanged after passage of 7000 column volumes of eluen t. A mechanism of retention is proposed, which fits the experimental o bservations.