4 Preparation of mixed standard solutionThe mixed standard solutions containing 75.7 mg/mLTCANa, 72.9 mg/mL CA, 61.4 mg/mL DCA, 80.0 mg/mLHDCA, 78.6 mg/mL CDCA, 75.7 mg/mL UDCA and56.0 mg/mL CHOL were prepared by adding an accuratelyweighed amount of each standard substance into avolumetric flask and dissolved with MeOH, and thenfiltered through 0.22 mm millipore membrane to yield themixed standard solutions.