Gas chromatography–tandem mass spectrometry assay for the quantification of four benzodiazepines and citalopram in eleven postmortem rabbit fluids and tissues, with application to animal and human samples

Pharmacokinetic studies and postmortem toxicological investigations require a validated analytical technique to quantify drugs on a large number of matrices. Three-step liquid/liquid extraction with online derivatization (silylation) ahead of analysis by gas chromatography–tandem mass spectrometry was developed and validated on rabbit specimens in order to quantify citalopram and 4 benzodiazepines (diazepam, nordazepam, oxazepam and temazepam) in 11 biological matrices (blood, urine, bile, vitreous humor, liver, kidney, skeletal muscle, brain, adipose tissue, bone marrow (BM) and lung). Since the 11 biological matrices came from the same animal species, full validation was performed on 1 matrix, bone marrow (considered the most complex), while the other 10 underwent partial validation. Due to non-negligible matrix effects, calibration curves were performed on each matrix. Within-day and between-day precision (less than 12.0% and 12.6%, respectively) and accuracy (from 88.9% to 106.4%) were acceptable on BM at both low and high concentrations. Assessment on the other matrices confirmed accuracy and within-day precision (less than 12%, and generally between 85.1% and 114.5%, respectively). The lower limit of quantification of the method was 1 ng/g for nordazepam, 5 ng/g for citalopram and 10 ng/g for oxazepam, diazepam and temazepam. The combination of 3-step extraction and MS/MS detection provided good selectivity in all matrices, including the most lipid-rich. Application to real-case samples showed that the method was sensitive enough to describe distribution patterns in an animal experiment, and specific enough to detect molecules in highly putrefied samples from human postmortem cases.