An alternative approach for preparation of amide-embedded stationary phase for reversed-phase liquid chromatography.

Polar-embedded stationary phases are superior to conventional alkyl stationary phases in terms of water-wettability, silanol activity and polar selectivity. A novel method was proposed for efficient preparation of amide-embedded stationary phases bearing extended aliphatic chain and large aromatic ring. The present approach, which simply required isocyanate and desired carboxylic acid, rather than the normal combination of amine/acyl chloride/proton scavenger, produced aromatic pyrenyl amide-embedded (PYE-Amide) and aliphatic docosanyl amide-embedded (C22-Amide) stationary phases. The as-synthesized packing materials were characterized and evaluated in comparison with conventional octadecyl stationary phases in terms of bonding density, aromatic and hydrophobic natures, charge-transfer capability, and selectivity towards isomers of various unsaturated compounds. A high affinity of the unsaturated ligand for the unsaturated solutes, especially the electron-deficient ones, was observed. The PYE-Amide stationary phase exhibited unique aromaticity-dependent shape selectivity, which was beneficial to the resolution of certain geometric isomers of polycyclic arenes. The applicability of such stationary phases was demonstrated by effective separations of estrogens and sulfonamide drugs.