Liquid-phase microextraction as a sample preparation technique prior to capillary gas chromatographic-determination of benzodiazepines in biological matrices

Liquid-phase microextraction (LPME) and gas chromatography were applied to determine diazepam and the main metabolite N-desmethyldiazepam in human urine and plasma. The analytes were extracted from 3.0–3.5 ml sample volumes directly into 25 μl of extraction solvent. The microextraction device consisted of a porous hollow fiber of polypropylene attached to two guiding needles inserted through a septum and a 4 ml vial. The hollow fiber filled with extraction solvent was immersed in sample solution. The extraction device was continuously vibrated at 600 rpm for 50 min. An aliquot (1 μl) of the extraction solvent with preconcentrated analytes was injected directly into the capillary gas chromatograph. Thirty samples were extracted simultaneously on the vibrator, providing a high sample capacity. The limits of detection were from 0.020 to 0.115 nmol/ml for diazepam and N-desmethyldiazepam in plasma and urine using a nitrogen–phosphorus detector (NPD).