Screening Procedure for Detection of Stimulant Laxatives and/or Their Metabolites in Human Urine Using Gas Chromatography-Mass Spectrometry after Enzymatic Cleavage of Conjugates and Extractive Methylation

Abstract

A gas chromatography-mass spectrometry (GC-MS)-based screening procedure was developed for the detection of stimulant laxatives and/or their metabolites in human urine after enzymatic cleavage of conjugates followed by extractive methylation. The part of the phase-transfer catalyst remaining in the organic phase was removed by solid-phase extraction on a diol phase. The compounds were separated by capillary GC and identified by computerized MS in the full scan mode. By use of mass chromatography with the ions m/z 305, 290, 335, 320, 365, 350, 311, 326, 271, and 346, the possible presence of stimulant laxatives and/or their metabolites could be indicated. The identity of positive signals in such mass chromatograms was confirmed by comparison of the peaks underlying full mass spectra with the reference spectra. This method allowed the detection of the diphenol laxatives bisacodyl, picosulfate, and phenolphthalein and of the anthraquinone laxatives contained in plant extracts and/or their metabolites in human urine samples. The overall recoveries of the stimulant laxatives and/or their metabolites ranged between 33% and 89% with a coefficient of variation of less than 15%, and the limits of detection ranged between 10 and 25 ng/mL (S/N 3) in the full scan mode. After ingestion of the lowest therapeutic dose of sodium picosulfate, its main metabolite, bisacodyl diphenol, was detectable in urine samples for 72 hours. After ingestion of the lowest therapeutic dose of a senna extract, the main metabolite of sennosides, rhein, was detectable in urine samples for 24 hours. This procedure is part of a systematic toxicological analysis procedure for acidic drugs and poisons with the modification of enzymatic cleavage of conjugates.