Internal-surface reversed-phase silica support for direct injection determination of drugs in biological fluids by...

A new internal-surface reversed-phase (ISRP) silica support has been designed for direct injection analysis of drugs in biological fluids by liquid chromatography. The support, prepared by using a new enzyme, polymyxin acylase, has N-octanoylaminopropyl phases, bound only to the internal surfaces of the porous silica, and N-(2,3-dihydroxypropyl)-aminopropyl phases on the external surfaces in order to be nonadsorptive to proteins. The average pore diameter of the prepared ISRP silica support was 50 A, which is small enough to exclude macromolecules such as serum proteins from the pores. The new ISRP support can be used for the direct injection analysis of hydrophilic and hydrophobic drugs in serum or plasma without destructive accumulation of proteins over the eluent pH range of 3 to 7. The recovery of drugs from serum was almost 100%, regardless of the difference in their protein bindings.