LC-MS as a tool to study toxic xenobiotics in biological fluids after oxidative metabolism

Introduction The detection of xenobiotic substances in human plasma and urine is of great concern in epidemiology, toxicology and forensic studies. Low concentration and extensive metabolism of active principles could reduce the possibility to confirm the presence of toxic analytes in biological fluids. The purpose of this study is to artificially produce degradation compounds similar to those formed in oxido/reductive metabolic pathways by adopting a photocatalytic process as a model-system and afterwards to identify them in biological samples, beside parent compounds. Liquid chromatography appears the best technique for direct analysis of these samples (neither derivatization nor complex extraction procedure for polar compounds), together with an ion trap MSn detection that empowers diagnostic identification and metabolites characterization. Methods Heterogeneous photocatalysis was performed on TiO2 by using a 1500 W xenon lamp in simulating AM1 solar light, in a device equipped with a 340 nm cut-off filter. LC-MS analysis were accomplished on a ion-trap instrument, with an Electrospray interface. Chromatographic separation were achieved on octadecylsilica reversed phase column. Photodegradation model was applied to scopolamine and cocaine. Studied substances and metabolites were found also in real samples coming from a toxicology laboratory. Preliminary results Tropane alkaloids are widely investigated compounds in forensic/toxicological chemistry. Scopolamine is one of the drugs used in sexual assaults to inhibit victim’s reaction. Many cases of such abuse were reported but less data are available in analytical chemistry literature. Cocaine, the well-known drug of abuse, belongs to this class too. Atropine is a dangerous contaminating compound in reported cases of street cocaine analysis. For this reason we have chosen these compounds to begin our study. Scopolamine and cocaine hold the same molecular weight, so that their contemporaneous presence in a real samples opens several analytical problems, above all about their metabolic pathways recognition. The use of MSn spectra analysis becomes absolutely necessary, due to the possibility of the formation of the same type of metabolic structures from both degradations, i.e. hydroxyl-derivatives, whose characterization can be achieved only by the utilization of MSn. In tropane alkaloids photocatalytic degradation, many oxidative potential metabolites were formed in the simulation model, beside some hydrolysis sub-products. Noteworthy is that hydroxy- atropine is isobaric with cocaine and scopolamine. Similar derivatives have been also found in real biological samples, both on rats and humans. Extension of this methodological approach to other compounds is at present in progress.