Development of Solid-Phase Extraction Coupled with Dispersive Liquid-Liquid Microextraction Method for the Simultaneous Determination of Three Benzodiazepines in Human Urine and Plasma

A new pretreatment method termed solid-phase extraction (SPE) which is combined with dispersive liquid–liquid microextraction (SPE-DLLME) has been developed for the determination of oxazepam, alprazolam and diazepam in urine and plasma samples. The analytes were extracted from biological samples using SPE followed by DLLME. Various parameters that affect the efficiency of the two extraction techniques have been optimized. The calibration plots were linear in the range of 2.5–500 µg L−1 for oxazepam, alprazolam and 1.0–500 µg L−1 for diazepam with detection limits of 0.7 µg L−1 for oxazepam, alprazolam and 0.4 µg L−1 for diazepam in plasma sample. The results confirm the suitability of the SPE-DLLME–HPLC-UV as a sensitive method for the analysis of the targeted analytes in urine and plasma samples.