Variation of intraindividual levels of endogenous GHB in segmented hair samples

Gamma-hydroxybutyrate (GHB) belongs to a group of substances that may be used in drug-facilitated crime (DFC). It is also an endogenous substance. There is a dispute whether or not a single exposure to GHB can be detected in hair. The first aim of this study was to develop and validate a method for the sensitive detection of base levels of GHB in hair. The second aim was to collect analytical data of 88 volunteers (62 females/26 males) not claiming any exposure to GHB and discuss the results in the context of the identification of a potential single exposure in cases of DFC. Furthermore hair samples from a male volunteer, who took GHB twice within 8 weeks, were analysed and the results were discussed with regard to mean values of endogenous GHB analysed in this study. Hair was digested under alkaline conditions, and GHB was isolated using liquid-liquid extraction. LC-MS/MS was performed using Electrospray ionization in the negative mode, multiple reaction monitoring, and a deuterated internal standard (GHB-D6). Segmental hair analysis revealed mean concentrations of 0.673ng/mg or 0.676ng/mg (without first segment) in females and 0.935ng/mg or 0.932ng/mg (without first segment) in males. Combined mean values were 0.751ng/mg and 0.752ng/mg (without first segment). In one individual's hair single doses of 2g GHB did not lead to an increase compared to his base levels. The limits of detection and quantitation in human hair were 0.1ng/mg and 0.3ng/mg, respectively. Accuracy at 0,25ng/mg, 2,5ng/mg and 25ng/mg was determined to be 94% or higher for all levels and intra-assay CVs at these concentrations were always lower than 7% (n=5). β-hydroxybutyrate (BHB) and glycine did not produce an interference. Recovery at 1ng/mg and 25ng/mg GHB was 23% and 13% and Matrix effects were calculated to be 77% and 89% respectively.