Simultaneous determination of barbiturates in human biological fluids by direct immersion solid-phase microextraction and gas chromatography–mass spectrometry

Simultaneous determination of seven barbiturates in human whole blood and urine by combining direct immersion solid-phase microextraction (DI–SPME) with gas chromatography-mass spectrometry (GC–MS) is presented. The main parameters affecting the DI–SPME process, such as SPME fibers, salt additives, pHs, extraction temperatures and immersion times were optimized for simultaneous determination of the drugs. The extraction efficiencies were 0.0180–0.988 and 0.0156–2.76% for whole blood and urine, respectively. The regression equations of the drugs showed excellent linearity for both samples; the correlation coefficients (r2) were 0.994–0.999. The detection limits for whole blood were 0.05–1 μg ml−1, and those for urine 0.01–0.6 μg ml−1. Actual quantitation could be made for pentobarbital in whole blood and urine obtained from volunteers, who had been orally administered a therapeutic dose of the drug. The DI–SPME/GC–MS procedure for barbiturates established in this study is simple and sensitive enough to be adopted in the fields of clinical and forensic toxicology.