Establish a robust technology for complex matrices and challenging agrochemical compounds.

To safeguard public safety and preserve biodiversity, it is crucial to closely observe pesticide concentrations. Mass Spectrometry (MS), combined with liquid chromatography (LC) has emerged as the preferred detection for pesticide detection and quantification. However, atmospheric pressure ionization (API) methods have limitations, including reduced spectral information, reproducibility issues, and challenges with poorly polar molecules and matrix effects, which complicate quantitative analyses and increase costs. To address these issues, alternative approaches have been explored, leading to the development of the Liquid Electron Ionization (LEI) interface, known for its robustness and consistency. LEI interface allows coupling the LC with the electron ionization (EI), extending it to low volatile and thermolabile molecules. In this dissertation, the LEI interface was involved in different qualitative, quantitative, and untargeted applications. The first part of the project, regarded the development of an innovative, rapid, and green pesticide quantification method based on LEI-MS. Two pesticides with different physical/chemical properties were analyzed simultaneously in a complex matrix. The system was centred on the direct coupling of a solid phase microextraction (SPME) fiber with LEI-MS, due to the use of a microfluidic open interface (MOI); the LC separation was not involved, allowing to perform compound extraction and analyses in about 5 minutes. The method proved to be reliable and reproducible. The second part of the project was focused on improving performance and demonstrating the versatility and advantages of the LEI interface. Coupling normal phase liquid chromatography (NPLC) with MS is a challenge due to the non-compatibility of the non-polar solvents with API techniques. For the first time, the system LC-LEI-MS was coupled with the NPLC. Different model compounds were analyzed, and the results showed that non-polar solvents did not affect the EI spectra, which were easily recognized using the NIST library. In addition, a real problem was solved using NPLC coupled with the LEI interface; a non-polar impurity was separated from the main compounds of the mixture in about 5 minutes, instead of the 50 minutes required in RPLC. In the last part of the project, the LEI interface was coupled with a high-resolution mass spectrometer (HRMS), a quadrupole-time-of-flight, hybrid instrument (Q-TOF), which was used for targeted and untargeted analysis in a forensic case involving Carbofuran (CBF), a carbamate pesticide banned by the EU. A novel workflow for untargeted analysis was developed by using HRMS, allowing for the identification of different compounds in different CBF formulations, required to understand the provenience of the formulation used. In addition, a quantitative method was developed to quantify CBF in animal samples. The use of CBF was confirmed, and the concentration of pesticide found in animal samples was compatible with the lethal dose (LD50). The same workflow was applied to identify an impurity in a formulation that had to be commercialized. So far, the LEI interface demonstrated its robustness and versatility in several applications, solving some problems that affect conventional ionization techniques. The next steps will focus on improving the sensitivity and making the interface more user-friendly; achieving these goals will expand the use of the LEI interface, establishing it as a crucial alternative for solving analytical challenges.