“…This would be of benefit not only for clinical research, but also for forensic analysis. Several methods have been reported for the determination of K and metabolites in various biological fluids, namely plasma [3,7,18,26] and urine [2,17,18,24,25,27,[28][29][30], using gas chromatography (GC) coupled to either mass spectrometry (MS) [2,18,24,30,31], tandem mass spectrometry (MS/MS) [11,12] or flame ionization detector (FID) [32]; or liquid chromatography (LC) with UV [3,5], MS [6] or MS/MS [22,23,25,27,33,34] detection. Sample preparation is usually performed by means of liquid-liquid extraction (LLE) [5,10,35] or solid-phase extraction (SPE) [7,17,23] procedures.…”