Determination of Diazepam in Human Plasma by Solid-Phase Microextraction and Capillary Gas Chromatography-Mass Spectrometry

A simple, sensitive, and reproducible solid-phase microextraction and capillary gas chromatography-mass spectrometry (SPME-GC-MS) method for determination of diazepam in human plasma is described. The optimum conditions for the SPME procedure were as following: direct extraction mode with a polydimethylsiloxane (PDMS) fiber (100 μm film thickness), 250 μL of sample plasma matrix modified with a solution containing sodium chloride (10% weight by volume) and 4.25 mL of a phosphate buffer solution (0.1mol L⁻¹, pH 6.9), extraction temperature 55°C under a magnetic stirring rate of 2500 rpm for 30 min, followed by the drug thermal desorption (250°C) in a GC injection port for 10 min. The limit of quantification of diazepam in plasma was 10.0 ng mL⁻¹, with a coefficient of variation lower than 14.0% and linearity from 10.0 to 1000.0 ng mL⁻¹, which allows diazepam analyses from sub to therapeutic levels.