Solid-phase microextraction and GC-ECD of benzophenones for detection of benzodiazepines in urine

Benzodiazepines are common drugs that cause intoxication. Benzodiazepines and their metabolites can be converted by hydrolysis in acid to the corresponding benzophenones, which are easier to be separated from matrices because of their hydrophobic properties. In this study, a new separation technique called solid-phase microextraction (SPME), which can integrate extraction, concentration, sampling and sample introduction into one single procedure, has been employed to extract the products of benzodiazepines from urine after acid hydrolysis. The extracts were determined by gas chromatography with electron-capture detection (GC-ECD). The hydrolysis conditions were optimized by a statistic orthogonal design. Factors influencing direct-immersion (DI)-SPME process were also checked and chosen experimentally. The method was evaluated with spiked human urine samples. The recoveries of nine benzodiazepines ranged from 1 to 25%, with the highest for oxazolam and the lowest for bromazepam. The calibration curves were linear from 10 to 500 ng/mL for oxazolam, haloxazolam, flunitrazepam, nimetazepam, and clonazepam and from 20 to 1000 ng/mL for the others except bromazepam. The detection limits were 2-20 ng/mL for most drugs tested. The intraday and interday coefficients of variation of the developed method were within 10 and 17%, respectively. In addition, the utility of the method was confirmed by determining two ingested benzodiazepines (flunitrazepam and oxazolam) in a volunteer's urine; urine flunitrazepam was still detectable 32 h after a therapeutic dose (1.2 mg) of the drug. Finally, the DI-SPME was compared with the conventional liquid-liquid extraction with regard to detection limits and extraction efficiency of the analytes. By DI-SPME, more amounts of analytes could be introduced into GC column than by conventional liquid-liquid extraction, and thus lower detection limits of the analytes were reached, although benzophenone recoveries by DI-SPME were rather low.