Since gamma-hydroxybutyric acid (GHB) is present in hair of the general population under physiological concentrations, special attention has to be given to the hair analysis of GHB and its interpretation. Normal levels of endogenous GHB can vary in each individual. As a result, strands of hair from a subject have to be cut in small segments (0.3-0.5 cm long) with analysis of each segment. As such, each subject can be used as its own control with a continuous endogenous signal. If one segment has a GHB concentration 10 times higher than the others, this suggests possible administration of exogenous GHB according to the UNODC guideline for Drug Facilitated Assault Cases.
Aim: As cosmetic treatments were found to decrease drug concentrations in hair, the aim of the study was to develop an UPLC®-MS/MS method for the analysis of GHB in hair. An in vitro study was then carried out in order to evaluate the impact of a hair straightener or a bleaching treatment on endogenous GHB concentrations.
Method: Hair samples (10 mg) were washed with dichloromethane and water. After drying overnight in an oven at 35 °C the samples were pulverized in disposable plastic tubes. Methanol/acetonitrile/ammonium formate buffer 1 mM (25:25:50, v/v/v) was used to extract the drug from the hair matrix in a water bath for 1.5 h at 37 °C. Thereafter, the samples were filtered and evaporated to dryness. The dried extracts were then reconstituted in mobile phase and injected in a UPLC®-MS/MS (Waters, Winslow, UK) with a BEH C18 column.
Results: The method was validated using untreated hair samples from three healthy volunteers. The calibration curve ranged from 0.06 to 25 ng/mg and the repeatability and intra-batch precision was lower than 20% evaluated in 8 different batches. Processed samples were stable for 3 days in the auto-sampler. To demonstrate the method applicability, 54 hair samples from healthy volunteers were analysed for endogenous GHB resulting in a concentration range from 0.2 to 6 ng/mg. Three different hair treatments experiments were carried out, in which a hair straightener and/or a bleaching treatment were applied. These experiments demonstrated that hair treatments decreased up to 80% of the GHB endogenous concentrations.
Conclusion: This in vitro study showed that hair bleaching or a heat source treatment influences GHB concentrations in hair. For a correct interpretation of GHB results in hair, cosmetic treatments should be considered, certainly in cases where only a part of the hair is treated.
Keywords: Bleaching; GHB; Hair; Heat; Straightening; UHPLC–MS/MS.
Copyright © 2019 Elsevier B.V. All rights reserved.