Development and Validation of Gas Chromatography-Flame Ionization Detection Method for the Quantification of Alprazolam Drug in Seized Narcotic Samples: Applications of Benzodiazepines in Forensic Drug Chemistry

Abstract

Alprazolam is a frequently misused psychotropic substance with counterfeit formulations posing major challenges for forensic laboratories. The present study reports the development and validation of a simple, rapid, and cost-effective gas chromatography–flame ionization detection (GC-FID) method for the quantification of alprazolam in seized narcotic samples. The method was optimized using a 5% phenyl methylpolysiloxane (5MS) capillary column using methanol as the extraction solvent. The method exhibited excellent selectivity, with no matrix interference. Linearity was demonstrated over the concentration range of 50–500 µg mL-¹, yielding a coefficient of determination (R²) ≥ 0.995. The limit of detection (LOD) and limit of quantification (LOQ), determined using the signal-to-noise approach, were 13.78 ppm and 14.62 ppm, respectively, confirming sufficient sensitivity for routine forensic applications. Recovery studies showed mean recoveries of 100.66%, 100.14%, and 99.88% for low (65 ppm), mid (220 ppm), and high (428 ppm) concentrations, all within the 80–120% acceptance criteria. Intra-day precision studies yielded percentage relative standard deviation (%RSD) values of 0.59%, 0.46%, and 0.57% across the same concentration levels, demonstrating high repeatability and robustness of the GC-FID system. Methanol proved to be the most effective extraction solvent compared to chloroform and acetonitrile, offering high recovery with minimal background interference. The developed GC-FID method provides a legally defensible, reliable, and accessible analytical approach for the quantification of alprazolam in seized drug samples by making it a practical alternative to mass spectrometry-based methods, particularly for laboratories with limited analytical resources.