Comparison of extraction procedures for benzodiazepines determination in hair by LC–MS/MS

Abstract

The use of a LC-MS/MS system for benzodiazepines detection remarkably increased the analytical sensitivity of these drugs in biological matrices, in particular in non-conventional ones such as hair. Since the amount of hair sample available for the analysis is frequently limited and, moreover, it needs to be checked for many other drugs and compounds of forensic interest, it is important to develop a sample preparation procedure able to detect either benzodiazepines and as many as possible other substances. The aim of this study was to compare the sensitivity of two different hair sample preparation procedures for benzodiazepines detection in hair. About 20mg hair, previously washed with organic solvent and cut into small pieces, were ultrasonicated with a phosphate buffer (pH 8.4) up to 1h and then extracted with dichloromethane/diethyl ether. The organic solvent was then dried under nitrogen flow and samples were reconstituted with 60μl methanol. Finally a 5μl aliquot was injected in the LC-MS/MS system. The second procedure consisted of an ultrasonication of hair samples in 700μl of methanol. Samples were then directly analyzed. Both the methods were fully validated. Thirty-five compounds among benzodiazepines and their metabolites were screened using both the procedures. The methods fulfilled all the validation parameters and were applied on either spiked blank hair and real positive samples. While phosphate extraction allowed to reach a LOQ for almost all the substances ranging from 0.1 to 5pg/mg, thus guaranteeing to evaluate even a single dose administration (as confirmed by real positive cases) the sensitivity of the methanol extraction showed a LOQ ranging from 1 to 20pg/mg, still enough to assess a therapeutic use of almost all the benzodiazepines; yet the methanolic incubation allows a simple and rapid analytical procedure due to the direct injection of the extraction solvent. Even though a methanol extraction procedure for benzodiazepines determination is useful for forensic toxicological purposes also when a wider range of substances is needed and in case of a small amount of hair available, it is advisable to prefer a phosphate extraction when detection of a single dose administration is required.