Enantiospecific High-Performance Liquid Chromatographic (HPLC) Determination of Baclofen and Its Fluoro Analogue in Biological Material

A method is described for the quantification of baclofen enantiomers in biological material (urine, plasma, and cerebrospinal fluid). The samples were extracted by liquid–solid extraction using Sep-Pak CIS cartridges. The subsequent derivatization procedure contained two separate steps. (1) The butyl esters of the enantiomers were formed using butanolic hydrochloric acid (followed by ion-pair extraction of the intermediate products). (2) A chiral derivatization was then performed using S-( + )-naproxen chloride as reagent. S-( + )-Benoxaprofen chloride can also be used. The diastereomeric amides were separated by high-performance liquid chromatography (HPLC) on a silica gel column (mobile phase, n-hexane/dichloromethane/ethanol; detection, fluorescence measurement at 335/365 nm). The described procedure was also used for the quantification of the fluoro analogue of baclofen. Urinary excretion of baclofen enantiomers was investigated in two healthy volunteers after p.o. administration.