Determination of lorazepam in plasma and urine as trimethylsilyl derivative using gas chromatography-tandem mass spectrometry.

A procedure based on gas chromatography-tandem mass spectrometry for identification and quantitation of lorazepam in plasma and urine is presented. The analyte was extracted from biological fluids under alkaline conditions using solid-phase extraction with an Extrelut-1 column in the presence of oxazepam-d5 as the internal standard. Both compounds were then converted to their trimethylsilyl derivatives and the reaction products were identified and quantitated by gas chromatography-tandem mass spectrometry using the product ions of the two compounds (m/z 341, 306 and 267 for lorazepam derivative and m/z 346, 309 and 271 for oxazepam-d5 derivative) formed from the parent ions by collision-induced dissociation in the ion trap spectrometer. Limit of quantitation was 0.1 ng/ml. This method was validated for urine and plasma samples of individuals in treatment with the drug.