Determination of ibuprofen in capillary and venous plasma by high-performance liquid chromatography with ultraviolet detection.

A high-performance liquid chromatographic (HPLC) method is described which determines ibuprofen in human capillary or venous plasma. Ibuprofen plus the internal standard, flurbiprofen, were extracted from acidified plasma with pentane-ether, back-extracted into base, and then extracted into the pentane-ether solution after acidification of the aqueous phase. A reverse-phase octadecylsilane column with acetonitrile-water-phosphoric acid as mobile phase and UV detection provided a quantifiable peak for 1 microgram/mL of ibuprofen in 0.1 mL of plasma. Capillary and venous plasma level curves were virtually superimposable after administration of 400 mg of ibuprofen to four normal volunteers. No ibuprofen was detected in the saliva of the subjects.