Rapid determination of γ-hydroxybutyric acid in human hair by on-line pyrolytic methylation-gas chromatography/mass spectrometry

•Online pyrolytic methylation-GC/MS was developed for the determination of GHB in human hair.•Low consumption of sample was achieved by the method without laborious pretreatment.•It required only one hair (0.3 mg) in every treatment, which can reduce the difficulty of sampling.•The developed method has profound significance for monitoring GHB abuse. A novel method based on on-line pyrolytic methylation-gas chromatography/mass spectrometry was established and applied into rapid determination of γ-hydroxybutyric acid (GHB) in human hair. With the pyrolytic methylation by tetramethylammonium hydroxide (TMAH), GHB was converted into its corresponding methyl ester in the pyrolyzer at 500 °C. Thus, GHB in hair samples could be well determined by GC/MS on a capillary column in SIM mode. To obtain optimum methylation conditions, important factors were investigated and then applied to the following experiments. The results were obtained as following: 500 °C as reaction temperature, 2:1 as the proportion of TMAH to GHB. The achieved calibration curve exhibited good linearity with the correlation coefficient of 0.9997 at the concentraion range of 2−200 ng/mg, and relative standard deviation (n = 3) from 1.3 %–7.7 %. The limit of detection and the limit of quantification were down to 0.3 ng/mg and 1.0 ng/mg, respectively. The precision ranged from 2.0 %–7.9 % and the recovery ranged from 98.5 %–107.4 %. The results of on-line pyrolytic methylation-GC/MS were in agreement with those observed by the referenced off-line silylation-GC/MS method. The method was applied to a real case of a woman addicted to GHB, the drug concentration in hair segments of 0−5 cm and 5−10 cm from the root strand well correlated with the use of GHB in different periods of her life. The proposed method demonstrated significant potential in the application of rapid determination for GHB in human hair.