Determination of low plasma timolol concentrations following topical application of timolol eye drops in humans by high-performance liquid chromatography with electrochemical detection.

A simple and sensitive high-performance liquid chromatographic assay was developed for determination of timolol in human plasma following administration of two drops of a 5% timolol ophthalmic solution. A 4% butyl alcohol-hexane extract of an alkalized sample of plasma was chromatographed on a reversed-phase column and the components in the column effluent were monitored by coulometric detection. The extraction efficiency of timolol was 69.02 +/- 4.16% (mean +/- S.D.) and its detection limit was 107.2 pg/ml. The effect of mobile phase pH, buffer concentration and the working potential of the detector on column performance and the electrochemical response are described.