Using a HPLC system (1200 rapid resolution system; Agilent Technologies, Santa Clara, CA, USA), liquid chromatographic separation was obtained on a 100 mm × 2.1 mm Acquity 1.7-m C18 column (Waters Corp, Milford, MA, USA). The flow rate was 0.25 mL/min and the column was kept at 40 °C. The following linear gradients of solvent A (2 mM ammonium formate in water) and solvent B (100% ACN) were used to elute samples from the LC column: −1 min, 0% B; 1–9.6 min, 0–98% B; 9.6–15 min, 98% B; and 15–18 min, 0% B. An Agilent Q-TOFMS (6510 Q-TOFMS; Agilent Technologies, Santa Clara, CA, USA) was used to perform mass spectrometry in both electrospray positive-ion (ESI+) and electrospray negative-ion (ESI-) modes. The scan range was 50–1000 m/z.
The capillary and skimmer voltages were set at 4000 and 65 V, respectively; the liquid nebuliser was set to 30 psig, the nitrogen drying gas was set at a flow rate of 10 L/min, and the drying gas temperature was maintained at 350 °C. Purine ([M-H] 121.050873), hexakis (1H,1H,3H-tetrafluoropropoxy) phosphazine ([M-H] 922.009798), purine ([M-H] 119.036320), and formate adduct ([M-H] 966.000725) were utilised as internal reference ions to ensure constant mass accuracy. Data were obtained using data acquisition software in profile mode (Agilent MassHunter Workstation, Agilent Technologies, Santa Clara, CA, USA).
The capillary and skimmer voltages were set at 4000 and 65 V, respectively; the liquid nebuliser was set to 30 psig, the nitrogen drying gas was set at a flow rate of 10 L/min, and the drying gas temperature was maintained at 350 °C. Purine ([M-H] 121.050873), hexakis (1H,1H,3H-tetrafluoropropoxy) phosphazine ([M-H] 922.009798), purine ([M-H] 119.036320), and formate adduct ([M-H] 966.000725) were utilised as internal reference ions to ensure constant mass accuracy. Data were obtained using data acquisition software in profile mode (Agilent MassHunter Workstation, Agilent Technologies, Santa Clara, CA, USA).