2.4.1 Determination of indican and indoxyl
The qualitative quantification of indican and indoxyl was performed using high-performance liquid chromatography (HPLC) (UV detector at 280 nm, EX1600, Exformma, USA). An Eclipse XDB C18 column (250 mm × 4.6 mm, Agilent, USA) was used for separation at a flow rate of 1.0 mL/min and the temperature of the column oven was 30 ℃. Mobile phase A (deionized water–acetic acid 100:0.5) and mobile phase B (acetonitrile). The elution ratio was A-80%: B-20% for 15 min. The UV detection wavelength was 240 nm.