Determination of endogenous concentration of γ-hydroxybutyric acid (GHB) in hair through an ad hoc GC-MS analysis: A study on a wide population and influence of gender and age

-Hydroxybutyric acid (GHB) spread for recreational purposes or as “rape drug” represents a hardissue for forensic toxicologists due to its endogenous nature. It is clear that an actual and reliablediscrimination between basal and exogenous levels is mandatory to achieve a correct evaluation ofconscious/unconscious administration. This research aimed to study the GHB baseline in hair samples,collected from 150 volunteers, non-consumers of any drugs of abuse, in order to evaluate if a genericcut-off value could be accepted, also focusing on potential influences of gender and age. The analysisconsisted of an overnight incubation with NaOH at 56◦C, liquid–liquid extraction with ethylacetate andtrimethylsylil derivatization. Detection was carried out through gas chromatography-mass spectrometryin single ion monitoring (m/z 233, 234, 147 for GHB; m/z 239, 240 and 147 for GHB-d6). The endoge-nous amount in “blank” hair was estimated by the standard addition method. Concentration range was0.279–2.839 ng/mg. In males, the average GHB levels were higher than in females (0.829 vs 0.596 ng/mg,respectively), especially in the first age category (<30 years, 1.008 vs 0.606 ng/mg, respectively). Ageinfluences on GHB levels seemed to be different among the two sexes: in male population concentrationswere higher <30 (1.008 ng/mg) and similar in the other age ranges (0.762 ng/mg, 30–50; 0.763 ng/mg,>50); in female, quite similar levels were registered throughout all the age categories (0.606 ng/mg, <30;0.536 ng/mg, 30–50; 0.691 ng/mg, >50). Further study should be performed on GHB physiology in orderto better understand these differences among ages and genders. Moreover, we demonstrated that for hairanalysis a cut-off reference value is not strictly mandatory, underlining the great interpretative valenceof segmental analysis.