REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC SEPARATION OF SMALL MOLECULES ON NONPOROUS-C18 SILICA-GEL COLUMN

Reversed-phase high-performance liquid chromatographic (RP-HPLC) separation of small molecules on a nonporous octadecylsilyl (C18) spherical silica gel was compared with the separation on conventional porous packings. Various alkylbenzenes were separated on three different types, nonporous, macroporous (pore diameter, 30 nm), and microporous (pore diameter: 10 nm), C18 bonded silica columns under both isocratic and gradient elution conditions. Under the isocratic conditions, column efficiency of nonporous silica was inferior to that of others. In case of the gradient elution, the nonporous silica column gave the most favorable separation in a short time. Fast separation of small molecules on the nonporous column could be performed by using a conventional HPLC system with a steep gradient condition, because the void volume of the nonporous packing was extremely smaller than the porous ones. Various series compounds such as fatty acid derivatives, phenylthiohydantoin (PTH) amino acids, and vitamins were well separated within 1 or 2 min on the C 18 nonporous silica column under steep gradient conditions.