2.4.2 Determination of indigo and indirubin
Indigo and indirubin were quantified using HPLC (UV detector at 280 nm, EX1600, Exformma). An Eclipse XDB C18 column (250 mm × 4.6 mm, Agilent) was used for separation at a flow rate of 1.0 mL/min and the temperature of the column oven was 35 ℃. Mobile phase A (deionized water–acetic acid 100:0.5) and mobile phase B (acetonitrile). The elution ratio was A-60%: B-40% for 10 min. The UV detection wavelength was 280 nm.