Gas Diffusion Microextraction Using a Cellulosic Membrane for the Gas Chromatography—Mass Spectrometry (GC–MS) Determination of Benzodiazepines in Urine

A gas diffusion microextraction (GDME) method coupled with gas chromatography–mass spectrometry (GC–MS) was developed and validated for the determination of diazepam, alprazolam, and lorazepam in urine samples. The procedure employs a headspace configuration using a low-cost cellulosic membrane as the gas-diffusion interface, allowing analyte transfer into a micro-volume methanolic acceptor phase while minimizing direct matrix contact. Key extraction parameters, including extraction temperature, time, and acceptor solvent volume, were optimized using a Box–Behnken experimental design. Under the optimized conditions (100 °C, 20 min, 200 µL methanol), the method exhibited excellent linearity in the range of 1–100 µg L−1, with coefficients of determination coefficient of determination (R2) ≥ 0.9987. The limits of detection ranged from 0.034 to 0.067 µg L−1. Intra-day and inter-day precision values were below 3.0% relative standard deviation (RSD) and the extraction recoveries were close to 100%. The analytical performance of the proposed GDME–GC–MS method was comparable to that reported for dispersive liquid–liquid microextraction (DLLME) and liquid-phase microextraction (LPME) based approaches. While the method requires elevated extraction temperature, its headspace-based configuration provides effective matrix isolation, making it a practical alternative for benzodiazepine determination in complex biological matrices such as urine.