Assay of total and free propranolol in plasma by liquid chromatography with fluorometric detection

We report a liquid-chromatographic method for assay of total and free propranolol and its metabolite, propranolol glycol, in plasma. An ultrafiltration device is used to separate the free drugs from the protein-bound drugs. The total and free drugs are isolated from plasma or ultrafiltrate by liquid-solid extraction on a Waters C18 SEP-PAK and the drugs are quantified on a C18 mu-Bondpak radial-compression column. The mobile phase consists of equal parts of methanol and a solution of potassium 50 mmol/L phosphate and 2.5 mmol/L 1-pentane-sulfonic acid, pH 5.0. Detection was by fluorescence, with excitation at 296 nm and emission at 338 nm. Time required for sample preparation for total-propranolol assay is 40 min per eight samples. Sample preparation for free-propranolol assay requires an additional 1 h per eight samples. Chromatography requires 15 min per sample. The extraction recovery is approximately 75% and the assay curve is linear from 5 to 400 micrograms/L. The run-to-run CV is 4% for total propranolol, 15% for free propranolol.