The analysis was carried out on an Acquity UPLC H-class (Waters, MA, USA) tandem QTRAP 5500 mass system (AB SCIEX, CA, USA). The separation was operated on a Waters Acquity UPLC BEH C18 column (2.1 × 50 mm, 1.7 μM particles) under gradient elution with mobile phase A (methanol) and mobile phase B (0.05% formic acid in water) as follows: initial, 10% A; 0 ~ 0.7 min 10% A– 90% A; 0.7 ~ 1.4 min, 90% A; 1.4 ~ 1.5 min, 90% A– 10% A; 1.5 ~ 3min, 10% A. The flow rate was 0.4 ml/min.
The positive electrospray ionization (ESI) was performed with optimal conditions as follows: ion spray voltage, 5500 V; temperature, 550°C; curtain gas, 30 psi; ion source gas 1 and ion source gas 2, 50 psi. The mass spectrometric analysis was operated in multiple reaction monitoring (MRM) mode with ion transitions at m/z 325.1 > 172.1 for quinidine, m/z 455.2 > 165 for verapamil and m/z 260 > 183 for propranolol, respectively. The negative ESI was performed under ion spray voltage of -4500 V for digoxin (m/z 779.4 > 649.2).
The positive electrospray ionization (ESI) was performed with optimal conditions as follows: ion spray voltage, 5500 V; temperature, 550°C; curtain gas, 30 psi; ion source gas 1 and ion source gas 2, 50 psi. The mass spectrometric analysis was operated in multiple reaction monitoring (MRM) mode with ion transitions at m/z 325.1 > 172.1 for quinidine, m/z 455.2 > 165 for verapamil and m/z 260 > 183 for propranolol, respectively. The negative ESI was performed under ion spray voltage of -4500 V for digoxin (m/z 779.4 > 649.2).