2.4. HPLC-HRMS

Reversed-phase chromatographic analysis was performed using a Agilent 1200 Series HPLC system (Agilent Technologies, Inc., Waldbronn, Germany) equipped with an Eclipse Plus C18 (ZORBAX, 3.5 µm, 2.1 × 150 mm, Agilent Technologies, Inc., Waldbronn, Germany). A flow rate of 0.3 mL min⁻¹ and a column temperature of 40 °C were used. Elution started with eluents A and B going from 99:1 to 70:30 within 1 min, followed by isocratic conditions of A and B 25:75 during the next 10 min. At 11.1 min, the solvent composition was set to 1:99 and hold for 0.1 min. At minute 15, the gradient was reset to starting conditions and held for further 15 min. For structure identification and recording concentration-time (c-t) curves, the HPLC system was coupled to an electrospray ionization (ESI) quadrupole time-of-flight mass spectrometer Agilent 6530 (Q-TOF-MS, Agilent Technologies, Inc., Waldbronn, Germany) with a Dual AJS electrospray ionization interface. The interface capillary temperature was set to 300 °C and the gas flow to 8 L∙min⁻¹. The fragmentor voltage was set to 125 V. Spectra were recorded in the positive ion mode with a mass range from 100 to 1000 m/z at a scan rate of 1 spectrum s⁻¹. Both instruments were controlled using MassHunter Workstation B.06.00 (Agilent Technologies, Inc., Waldbronn, Germany).