Detection of gamma-hydroxybutyrate in hair: Validation of GC–MS and LC–MS/MS methods and application to a real case

A gas chromatography–mass spectrometry (GC–MS) and a liquid chromatography tandem mass spectrometry (LC–MS/MS) method were validated for quantifying endogenous and exogenous hair concentrations of gamma-hydroxybutyrate (GHB). The GC–MS method is based on overnight extraction of 25 mg hair in NaOH at 56 ◦C, liquid/liquid extraction in ethylacetate and trimethylsylil derivatization; analysis is by electron ionization and single ion monitoring of three ions. The LC–MS/MS method entails a rapid digestion of 25 mg hair with NaOH at 75 ◦C for 40 min, liquid/liquid extraction in ethylacetate and reconstitution of the extract in the LC mobile phase; negative ion electrospray ionization and multiple reaction monitoring (MRM) analysis are employed for the LC–MS/MS detection. In both cases, GHB-d6 is used as an internal standard. The endogenous amount in “blank” hair are estimated by the standard addition method. Limits of detection are 0.4 and 0.5 ng/mg for GC–MS and LC–MS/MS respectively, while the limit of quantification (LOQ) is 0.6 ng/mg for both methods; the GC–MS method proved to be linear in the range 1–50 ng/mg whereas linearity was demonstrated from 0.6 to 50 ng/mg for the LC–MS/MS; imprecision and inaccuracy were always lower than 23% for quality controls samples. The two methods were applied to a real case of a man addicted to GHB; the drug concentration in segments from 17 cm hair strand well correlated with self-reported use of GHB in different periods of his life. Performances of the two methods were similar.