3.9. Electrospray Mass Spectrometry (ESI-MS) Analysis

The high-resolution mass spectrometer used was an Orbitrap Q-Exactive (Thermo Scientific, Milan, Italy) equipped with an HESI II interface set in positive (ESI(+)) polarity. A Q-Exactive mass spectrometer was operated in full scan (70 000 FWHM). Mass spectra were recorded from m/z 400 to 2000. Acquisition parameters were optimized by direct infusion of standard working solutions of the analytes (50 µM in water) at a flow rate of 3 μL min⁻¹ into the ESI interface of the mass spectrometer. The parameters were optimized as follows: spray voltage set at 3.5 kV (ESI(+)), capillary temperature set at 300 °C; sheath, auxiliary, and sweep gases (nitrogen) fixed at 5, 0, and 0 (arbitrary unit), respectively. Acquisition data were recorded and elaborated using Xcalibur™ version 3.0 software from Thermo Fisher.