Determination of pindolol in biological fluids by electron-capture GLC

An electron-capture GLC method was developed for measuring pindolol in human plasma and urine. The unchanged drug was extracted with benzene from alkalinized plasma or urine using propranolol as the internal standard. Both compounds subsequently were back-extracted into 0.1 M HCl and then into benzene. After evaporation of the organic phase, the compounds were derivatized with trifluoroacetylimidazole to form the trifluoroacetyl ester of pindolol and propranolol. These derivatives then were analyzed by electron-capture GLC. The method allowed the measurement of concentrations as low as 1 ng of pindolol/ml of plasma and was applied successfully to determinations of plasma levels in humans after oral administraton of a single 10-mg dose of pindolol.