Deoxycholic acid

Chromatographic grade methanol and acetonitrile (ACN) were acquired from Merck (Darmstadt, Germany). Ammonium acetate (LC-MS grade) and chenodeoxycholic acid were purchased from Sigma-Aldrich. Deionized water prepared by a Milli-Q system (Millipore, MA, USA) was used as a solvent. GCA pure substance and its isotopically labeled internal standard (IS) glycocholic-2,2,4,4-d4 acid (GCA-d4) were obtained from Mikromol (LGC Standards GmbH, Germany) and Toronto Research Chemicals (Toronto, Canada), respectively. Hyodeoxycholic acid, ursodesoxycholic acid, deoxycholic acid, taurocholic acid, cholic acid, and glycochenodexycholic acid were all purchased from MACKLIN (MACKLIN, Shanghai). Glycodeoxycholic acid was obtained from Aladdin (Aladdin, Shanghai). Glycoursodeoxycholic acid was obtained from RHAWN (RHAWN, Shanghai). The mixed-mode anion exchange Oasis MAX SPE cartridges (1 cc, 30 mg) were purchased from Waters. The weights of the samples and standard solutions were performed on a Mettler Toledo XPE205 balance with the readability of 0.01 mg. The serum for the method validation and comparison was obtained from the remaining samples of the company's kit study.

Chitosan (CS, viscosity < 200 mPa.s, 97.8% deacetylated), N-acetyl-L-cysteine (NAC), 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC), deoxycholic acid (DA), and succinic anhydride (SA) were purchased from Macklin (Shanghai, China). Both E. coli (CMCC(B) 44103) and S. aureus (ATCC 25923) were from the China Center of Industrial Culture Collection, Beijing, China. In addition, methanol, ammonia, glacial acetic acid, ethanol, acetone, and DMSO were from Guanghua Technology Co., Ltd. (Shantou, China). The reagents and chemicals were all of analytical grade and were not further purified. All experiments used ultrapure water.