A systematic comparison of four different workup procedures for systematic toxicological analysis of urine samples using gas chromatography–mass spectrometry

Abstract

Sample preparation for systematic toxicological screening analysis (STA) in urine by gas chromatography-mass spectrometry (GC-MS) generally involves cleavage of conjugates by acid hydrolysis (Hy) or enzymatic hydrolysis (Gluc) followed by liquid-liquid extraction (LLE) or solid-phase extraction (SPE), and derivatization, e.g., acetylation (Ac). LLE and derivatization can be performed simultaneously, e.g., in extractive methylation (ExMe). The work presented consisted of two separate studies. In study I, 350 urine samples from 168 inpatients from an internal medicine ward were worked up by Hy-LLE-Ac, the standard workup in the authors' laboratory, Gluc-SPE-Ac, and Gluc-ExMe. In study II, 100 urine samples from psychiatric inpatients were worked up by Hy-LLE-Ac and Hy-SPE-Ac. The samples prepared were analyzed by full-scan GC-MS, and the drugs and/or their metabolites/artifacts detected after the different workup procedures were compared. The results obtained after Hy-LLE-Ac and Gluc-SPE-Ac showed only little differences, e.g., salicylic acid not being detectable with the latter. Hy-SPE-Ac covered a similar range of analytes as Hy-LLE-Ac but was much more time-consuming. Comparison of Hy-LLE-Ac and Gluc-ExMe showed that the former was better suited for basic drugs and the latter for acidic drugs, but the overlap was considerable. In conclusion, Hy-LLE-Ac remains the method of choice for STA in clinical toxicology owing to its wide analyte spectrum and short workup time. Gluc-ExMe is an ideal complementary method when acidics need to be covered. Gluc-SPE-Ac can be used as an alternative to Hy-LLE-Ac when turnaround is not critical or when automated analysis is required.