Mass spectrometry pneumatically assisted desorption/ionization in forensic toxicology

Mass spectrometry is one of the most relevant techniques in clinical and forensic toxicology. Its development and improvement are based on the invention and utilization of new ion sources, new ionization methods, new mass analyzers and new sample pre-treatment techniques. A recent innovation is the ability to record mass spectra on ordinary samples in their native environment, without sample preparation or pre-separation. In this field, a new desorption ionization method called DESI (Desorption Electrospray Ionization) has been described; subsequently, method called DeSSI (Desorption Sonic Spray Ionization), at first sight similar to DESI, but in deep substantially different, has been developed. This thesis consist in developing a new desorption/ionization interface to investigate the real mechanism involved in ions formation because we considered that propaedeutic for the extensive use of the method in the toxicological analytical field. We verified that the pneumatic contribution is preponderant to the obtained results. Hence, our new desorption/ionization interface uses only a spray of pure solvent with no high voltage on needle. A key aspect of this project, applied to several complex matrix, is the number of controllable operating parameters that can be investigated and optimized to obtain an efficient surface analysis. The most important variables are taken in consideration were the source geometry (the spray angle and the ion uptake angle, as well as the various distances in aligning the spray, sample and mass spectrometer) and the characteristic of sprayer (contents of the solvent spray and gas flow rate). All measurements have been performed in positive and negative ionization conditions, varying capillary voltage, nebulizing gas pressure, drying gas flow and end plate temperature. Acquisition was in multiple mass spectrometry mode (MSn). 2 We have applied this new technical solution to compound identification, active principles and drugs identification in direct tablet analysis, active principles and drugs identification in vegetable species. Future developments will be related to apply the direct analysis of analytes present on the original surfaces of interest in the toxicological field for in vivo sampling of living tissue surfaces, to identify drug and xenobiotic exposure, besides the chemical imaging of spatial distribution of analytes onto sample surfaces.