Determination of flunitrazepam and its main metabolites in serum and urine by HPLC after mixed-mode solid-phase extraction.

A rapid and sensitive method is presented for the simultaneous determination of flunitrazepam, norflunitrazepam, 7-aminoflunitrazepam, and 7-acetamidoflunitrazepam in serum, plasma, and urine. The compounds were extracted by a mixed-mode solid-phase procedure following analysis by high-performance liquid chromatography and ultraviolet detection and using methylclonazepam as the internal standard. The method revealed high recoveries and showed good precision and linearity for all compounds. The limit of detection was at least 1 ng/ml serum (plasma) for all compounds.