Gas chromatographic-mass spectrometric method for the determination of flurazepam and its major metabolites in mouse and rat plasma.

A capillary gas chromatographic-negative chemical ionization (NCI) mass spectrometric method for the determination of flurazepam and its metabolites N-1-hydroxyethyl-flurazepam and N-1-desalkyl-flurazepam in mouse and rat plasma was described. Derivatization of the metabolites of flurazepam with BSTFA allowed a highly stable, accurate, and sensitive GC-MS analysis. The use of a single internal standard (halazepam) for the quantification of all compounds saved cost and time. The detection limits were 0.1 ng/ml for N-hydroxyethyl-flurazepam-TMS (M(r) = 404), 0.5 ng/ml for desalkyl-flurazepam-TMS (M(r) = 360), and 0.5 ng/ml for flurazepam (M(r) = 387) with an injection volume of 1 microliter at a signal-to-noise ratio greater than 5. The quantitation limit was set to 10 ng/ml for all compounds.