Measurement of penbutolol and 4‐hydroxypenbutolol in plasma or serum by HPLC

A simple HPLC method for penbutolol and 4‐hydroxypenbutolol assay has been developed. Plasma or serum (200 μl) is vortex‐mixed (30 s) with Tris solution (2 M , pH 10.6) containing an internal standard (50 μl) and methyl t‐butyl ether (200 μl). After centrifugation, the extract (100 μl) is analysed using an unmodified silica column (250 × 5 mm ID) and iso‐octane–methanol–methyl t‐butyl ether (55:25:20) containing ammonium perchlorate (10 m M , pH 5.7) as eluent and with fluorescence detection. No interference has been encountered and the limit of accurate measurement for both compounds is 5 μg/l.