Evaluation of a liquid electron ionization liquidchromatography–mass spectrometry interface

Liquid Electron Ionization (LEI), is an innovative liquid chromatography-mass spectrometry (LC–MS)interface that converts liquid HPLC eluent to the gas-phase in a mass spectrometer equipped with anelectron ionization (EI) source. LEI extends the electronic spectra libraries access to liquid chromatog-raphy, providing a powerful tool in the untargeted approacssh. Negligible matrix effects allow accuratequantitative information. The purpose of this research was to evaluate the main aspects concerning theinterfacing process. These fundamental studies were necessary to understand the mechanism of LEI indetails, and improve the interfacing process, especially regarding robustness and sensitivity. Hardwarecomponents were installed to prevent analytes precipitation, reduce thermal decomposition of sensitivecompounds, and to stabilize the nano-flow delivery with different mobile-phase compositions. Partic-ular attention was devoted to insulating the heated vaporization area from the LC part of the system.Experiments were performed to optimize the interface inner capillary dimensions, and other operativeparameters, including temperature, gas and liquid flow rates. Test compounds of environmental interestwere selected based on molecular weight, thermal stability, volatility, and polarity. Robustness was eval-uated with a set of replicated injections and calibration experiments using a soil matrix as a test sample.MRM detection limits in the low-picogram range were obtained for five pesticides belonging to differentclasses in a soil sample. High-quality electron ionization mass spectra of a mixture of pesticides werealso obtained.