Determination of γ-hydroxybutyric acid (GHB) in plasma and urine by headspace solid-phase microextraction and gas chromatography/positive ion chemical ionization mass spectrometry

A new method for the qualitative and quantitative analysis of γ‐hydroxybutyric acid (GHB) in plasma and urine samples is described. It involves the conversion of GHB to γ‐butyrolactone (GBL), its subsequent headspace solid‐phase microextraction (SPME), and detection by gas chromatography/positive ion chemical ionization mass spectrometry (GC/PICI‐MS), using D6‐GBL as internal standard. The assay is linear over a plasma GHB range of 1–100 µg/mL (n = 5, r = 0.999) and a urine GHB range of 5–150 µg/mL (n = 5, r = 0.998). Relative intra‐ and inter‐assay standard deviations, determined for plasma and urine samples at 5 and 50 µg/mL, are all below 5%. The method is simple, specific and reasonably fast. It may be applied for clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring. Copyright © 2000 John Wiley & Sons, Ltd.