LC-MS/MS Determination of Hair GHB: Is Segmental Analysis Useful for Exogenous Discrimination?

Discrimination between endogenous and exogenous Gamma-hydroxybutyrate (GHB) in hair matrix is a major challenge in the forensic context. According to the UNODC, to verify a possible intake, GHB concentration should be compared with the subject's basal level. Most published studies investigated endogenous GHB on a single hair segment, without considering possible intra-individual variation. The present study aimed to detect endogenous GHB in hair using a newly validated method, with a focus on the relevance of segmental analysis. Two hundred subjects were tested. After the removal of the first 0.5 cm from the proximal end, each hair strand was divided into three segments of 1 cm. A water extraction was performed during the pulverization process, and the extract was injected into a LC-MS/MS system. Data have been statistically analyzed. Overall, endogenous GHB concentration ranged from < LOD (0.1 ng/mg) to 6.6 ng/mg, with 27% of samples having a value < LOD in at least two segments. Within the remaining subjects, neither gender nor age significantly influenced the concentration. On the other hand, results confirmed that hair treatment can modify endogenous GHB concentrations. Intra-individual variability was limited, with the highest percentage of cases showing minimal changes in concentration (0-0.1 ng/mg) between contiguous segments. However, in up to 4% of cases, the variation resulted to be higher than 1 ng/mg between contiguous segments. The present study then confirms the need to perform in forensic cases the segmental analysis, to be sure that any potential increase of GHB depends exclusively on external administration.