Sviluppo di micro-tecniche "green" per l'analisi chimica

Compound discovery is of increasing importance in various fields such as environmental, food safety, forensic, and other investigation areas where the presence of non-targeted compounds represents a key factor. The actual trend is towards the identification of developing threats and potential safety issues, at their early stages, through non-targeted monitoring analysis technologies. Liquid chromatography coupled to mass spectrometry (LC-MS) has demonstrated to be the best technique and plays a central role in routine analysis, whereas gas chromatography-mass spectrometry (GC-MS) is limited to those volatile substances that are suitable for gas-phase separation. Electrospray (ESI) is one of the most frequently used LC-MS ionization techniques, thanks to its specificity, detection limits, and flexibility. However, ESI response is influenced by the chemical background and limited by the nature of the analyte. Because the ionization is based on a low energy chemical reaction, the fragmentation is weak and lacks structural information. Conversely, electron ionization (EI) is not influenced by the nature of the analyte and matrix composition. It provides 70 eV spectra that can be compared with those recorded in electronic libraries that acts as a molecular fingerprint. Considering that EI-MS works appropriately in gas-phase and high-vacuum conditions, coupling it with liquid chromatography is a challenging goal. An innovative liquid chromatography-mass spectrometry interface is presented and discussed. This new interface, called Liquid-EI (LEI), is based on electron ionization but it differs from other previous attempts because analyte and mobile phase vaporize before entering the ion source. The vaporization takes place at atmospheric pressure into a specifically designed chamber called vaporization micro-channel, placed between the LC apparatus and the high-vacuum ion source. The interface is entirely independent and can be a compelling upgrade for every GC-MS system providing a rapid and reversible LC-MS conversion. A commercial fused silica liner, placed inside the vaporization micro-channel, acts as an inert vaporization surface, speeding up the gas-phase conversion of large molecules while lessening possible memory effects. The liner is a replaceable component for simplified maintenance. LEI extends the NIST libraries access to liquid chromatography, providing a powerful tool in the untargeted approach. To optimize the liquid-to-gas conversion efficiency, several upgrading has been developed to make this step takes place only inside the vaporization micro-channel. The advantages of using LEI are various; because the ionization is a physical process, it is not influenced by the chemical properties of the analyte and the chemical background. These features allow the system to have no polarity limitation and minimized matrix effects. Using LEI high-quality EI spectra are acquired, speeding up the compound discovery process. Its highlights are of great potential for flexible and direct targeted and non-targeted approaches. The development, the optimization and several different applications based on the use of LEI-LC-MS are here presented and explained.