Instrument and conditions
Shimadzu 8040 Tandem Mass Spectrometer (Shimadzu, Japan) was used equipped with electrospray ionization in the negative ion mode. Optimum seperation conditions were obtained with Shiseido Capcell PAK C18, 250 x 4.6 mm, 5 µm with mobile phase consisting of water and acetonitrile (15/85, v/v) with column oven temperature maintained at 30°C. Flow rate was 1.2 mL/min. The multiple reaction monitoring (MRM) transitions were performed at m/z 156.1˃113.1and 158.1˃113for favipiravir and [13C15N] Favipiravir, simultaneously. Total run time for the method was 3.5 min. The nebulizing gas and drying gas flow rates and the ESI voltage were 2.5 L/min, 15 L/min and 5500 V, respectively. The gas used for nebulizing and drying was high pure nitrogen generated by Peak Scientific NL-60. Shimadzu LabSolutions Software version 5.93 was used for data acquisition and evaluation of chromatographic data.