Phase I metabolites (organic acids) of gamma-hydroxybutyric acid-validated quantification using GC-MS and description of endogenous concentration ranges.

Gamma-hydroxybutyric acid (GHB) is a sedative drug used in drug-facilitated crimes. Its detection window is very short. GHB undergoes intensive phase I metabolism to organic acids (glycolic acid, succinic acid, dihydroxybutyric acids). These could be potential analytical targets to broaden the detection window. The aim of the present study was to enable the detection of endogenous levels of these metabolites in biological samples (blood and urine). A gas chromatographic-mass spectrometric method using liquid-liquid extraction and derivatization with N-methyl-N-tri-methylsilyltrifluoracetamide was developed for the quantification. Validation results were consistent with international guidelines, and the method was able to quantify endogenous levels of the substances in both urine and blood. Endogenous concentrations were shown to be <0.03-4.92 mg/L for glycolic acid, <0.03-1.28 mg/L for GHB, <0.28-18.1 mg/L for succinic acid, <0.12-1.38 mg/L for 2,4-dihydroxybutyric acid, and <0.13-2.59 mg/L for 3,4-dihydroxybutyric acid in serum samples of 101 volunteers. Urinary endogenous concentrations were shown to be 1.30-400 mg/L for glycolic acid, <0.03-1.94 mg/L for GHB, 1.17-2.73 mg/L for succinic acid, 0.72-26.2 mg/L for 2,4-dihydroxybutyric acid, and 1.88-122 mg/L for 3,4-dihydroxybutyric acid in urine samples of 132 volunteers. These endogenous concentrations represent a basis to which concentrations after the intake of GHB can be compared to in order to prove the intake of this substance.