HIGH-PERFORMANCE CHIRAL DISPLACEMENT CHROMATOGRAPHIC SEPARATIONS IN THE NORMAL-PHASE MODE .1. RETENTION AND ADSORPTION STUDIES OF POTENTIALDISPLACERS DEVELOPED FOR THE PIRKLE-TYPE NAPHTHYLALANINE SILICA STATIONARY-PHASE

Three families of potential displacers have been designed and synthesi zed for use with the Pirkle-type naphthylalanine silica stationary pha ses operated in the normal-phase mode. The displacers contain a pi-aci d head group (3,5-dinitrobenzoate, 3,5-dinitrobenzamide or 3,5-dinitro phenylcarbamate groups), an H-bonding mid-section (C=O and/or NH group s) and a solubility adjusting tail section (n-alkyl groups). By varyin g the length of the alkyl chain between methyl and tetracosanyl, a lar ge number of homologous compounds were synthesized in each family. The capacity factors of the homologues were measured in n-hexane-tetrahyd rofuran eluents; the k' values vary regularly with both the tetrahydro furan concentration of the eluent and the length of the alkyl chain. T he individual excess adsorption isotherms of the homologues were also determined and the isotherm parameters were correlated with the length of the alkyl chain. Because the capacity factors and the adsorption s trengths of these compounds cover a broad range, they can serve as dis placers in a variety of normal-phase chiral displacement chromatograph ic separations.