Characterization of an internal-surface reversed-phase silica support for liquid chromatography and its application to assays of drugs in serum.

Internal-surface reversed-phase (ISRP) silica supports having N-octanoylaminopropyl phases bound to the internal surfaces of the porous silica and N-(2,3-dihydroxypropyl)aminopropyl phases bound to the external surfaces were synthesized from silica particles differing in nominal pore diameters and specific surface areas. These ISRP supports were characterized with regard to physical and chromatographic properties. The support with an N-octanoylaminopropyl phase coverage of 485 mumol/g and an average pore diameter of 65 A was the most suitable for the direct-injection determination of hydrophilic or hydrophobic drugs in serum or plasma. Non-steroidal anti-inflammatory (acetylsalicylic acid and salicylic acid) and tricyclic antidepressant drugs (desipramine and nortriptyline) in serum were successfully determined with this support and an acidic eluent.