High-performance liquid chromatographic and gas-liquid chromatographic determination of diazepam and nordiazepam in plasma.

A one-step method for extraction of diazepam, nordiazepam, and internal standard into toluene is followed by chromatographic separation and detection with either dual-wave-length high-performance liquid chromatography or electron-capture gas-liquid chromatography. Agreement between the two methods was excellent for diazepam (r = 0.99, n = 38) and good for nordiazepam (r = 0.96, n = 79) over a concentration range that included subtherapeutic, therapeutic, and toxic plasma levels.