“…Easier assays all use liquid chromatography with fluorescent detection after an ethereal liquid-liquid extraction [7,8], automated solid-phase extraction [9] or on-line extraction [10] procedure. In addition, protein precipitation with acetonitrile was investigated shortly as an alternative for liquid-liquid extraction by Koppel et al [8]. Despite its poorer sensitivity this can be a useful, fast and easy option for pharmacokinetic evaluations.…”