Micro-extraction of commonly abused benzodiazepines for urinary screening by liquid chromatography

We have developed a micro-extraction procedure for the analysis of seven commonly prescribed benzodiazepines (chlordiazepoxide, diazepam, lorazepam, nitrazepam, nordiazepam, oxazepam, and temazepam) in urine using liquid chromatography. The method is reliable and sensitive, uses small volumes (100 mu L) of urine and is suitable for the detection and quantification of low concentrations of benzodiazepines. The micro-extraction procedure allowed rapid sample processing, which is important for routine sample handling. The limit of detection for the seven benzodiazepines ranged from 0.10-0.71 mg/L and recovery of the different benzodiazepines was good, ranging from 70-105%. Between- and within-assay coefficients of variation ranged from 6.3% to 13.8%, and 2% to 3.5%, respectively. Chlordiazepoxide chromatographed poorly (between assay coefficient of variation 35.4%, within-assay 7%), and we set the cut-off value for this compound at 5.0 mg/L.