Highly specific and sensitive method for the determination of flunitrazepam in plasma by electron capture gas-liquid chromatography.

A sensitive and highly specific electron capture gas-liquid chromatographic method was developed for the determination of flunitrazepam in human plasma. The method involves selective extraction of the drug into hexane from plasma at pH 9 followed by back-extraction into 2 N sulfuric acid for clean-up procedure, and re-extraction by 20% toluene-hexane at pH 2. The sensitivity limit of the method is 0.5 ng/ml of plasma. Its specificity was tested for about 45 drugs frequently administered as co-medication in hospitalized patients, including other benzodiazepines. The method proves very suitable for investigating the clinical pharmacokinetics of flunitrazepam as well as for monitoring therapeutic plasma levels and in forensic situations following over-dosage, and was successfully applied within a clinical pharmacokinetic study in an intensive care unit.