Enantioselective quantitation of (R)- and (S)-alprenolol by gas chromatography-mass spectrometry in human saliva an plasma

An enantioselective gas chromatographic-mass spectrometric assay is developed for alprenolol and its metabolite, 4-hydroxy-alprenolol, in saliva and plasma. The procedure is based on a two-step derivatization technique with N-heptafluorobutyryl-l-prolylchloride and N-methyl-N-trimethylsilyl-trifluoroacetamide, followed by a gas chromatographic separation with mass spectrometric detection of the diastereomeric derivatives. A selected ion chromatogram extracted from full scan data shows that the respective enantiomers of alprenolol, 4-hydroxy-alprenolol, and the internal standard (ions at m/z 481) are well-separated in saliva and plasma. Linear and reproducible calibration curves are obtained over the concentration ranges 1.67-13.33 ng/mL and 2.50-20.00 ng/mL enantiomer in saliva and plasma, respectively. The performance of the method for alprenolol, in terms of accuracy and precision, fits well within the generally accepted criteria for validation. The enantioselective assay is successfully used in a study involving a single oral dose of alprenolol administered to two healthy volunteers. Stereoselective differences are observed in the saliva and plasma concentrations following an oral dose of 50 mg (R,S)-alprenolol hydrochloride.