Isothermal gas chromatographic analysis of diphenhydramine after direct injection onto a fused-silica capillary column.

The packed column injector of a gas chromatograph was modified to accommodate direct injection by syringe onto a wide-bore fused-silica capillary column. No changes were made to the nitrogen-phosphorus detector. The resultant configuration combines fast separations with precise quantitations. The analysis of diphenhydramine in serum is presented as an application. Chromatographic separation of diphenhydramine and orphenadrine (internal standard) from caffeine and other endogenous material takes 2 min. Serum diphenhydramine concentrations are presented for six volunteers following a 50-mg oral dose.