Acetic acid

The standards N-butyryl-L-HSL (C4-HSL) and N-(3-oxododecanoyl)-L-HSL (3-oxo-C12-HSL) were purchased from Sigma. Methanol, acetonitrile (HPLC grade), and formic acid (MS grade) were purchased from Fisher Scientific (Loughborough, UK). Acetic acid and ethyl acetate (HPLC grade) were obtained from Guangzhou Chemical Reagent Factory (Guangzhou, China), and ultra-pure water (>18 MΩ/cm) was obtained from a Milli-Q water Elga Maxima water purification system (Merck KgaA, Germany).

TYL was brought from Hengtong Guanghua Factory (Xi’an, China), and ROX, SPM, JOS, and CLA were from European Pharmacopoeia (EDQM, Strasbourg, France). KIT, ERY, TIL, TUL, and AZI were obtained from Sigma Chemicals Co. (St. Louis, MO, USA). MED was obtained from the China Institute of veterinary drugs control (Beijing, China). The purity of each analytical standard is higher than 92.5%. The chromatographic grade methanol, acetonitrile, and formic acid (FA) were purchased from Fisher Scientific (Fairlawn, NJ, USA). Other organic solvents such as ammonium hydroxide, acetic acid, and chloroform were analytical grade and brought from Guangzhou Chemical Reagent Factory (Guangzhou, China). Ultrapure deionized water was produced by a Millipore MilliQ water system (Molsheim, France). C₁₈ (200 mg, 3 mL) and SCX (60 mg, 3 mL) SPE cartridges were available from Agilent Technologies Co. (Santa Clara, CA, USA). The Oasis HLB cartridge (60 mg, 3 mL) was obtained from Waters Co. (Milford, MA, USA).
The stock standard solution (1.0 mg/mL) of each compound was prepared by dissolving 10 mg of analytical standard in 10 mL of methanol and can be stored at −20 °C for 3 months. Working solutions were obtained by diluting the stock solution with methanol, daily, according to practical requirements.

Vanillin was purchased Shanghai Sangon Biological Engineering Technology (Shanghai, China). o-Toluidine and N, N-dimethylformamide were purchased from Shanghai Aladdin Bio-Chem Technology Co., LTD (Shanghai, China). Sodium citrate tribasic dihydrate and Tris were purchased from Sigma-Aldrich (Steinheim, Germany). Glycine was purchased from GenStar Biosolutions Co., Ltd. (Beijing, China). Citric acid, disodium hydrogen, HCl, NaOH, Na₂HPO₄ and acetic acid were purchased from Guangzhou Chemical Reagent Factory (Guangzhou, China). Acetonitrile was purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). n-Hexane was purchased from Chengdu Kelong Chemical Reagent Factory (Chengdu, China). Other chemicals were purchased from standard commercial sources and were of analytical grade purity.

Metformin Hydrochloride (C₄H₁₁N₅·HCl, purity 100.0%), glyburide (C₂₃H₂₈ClN₃O₅S, purity > 99.9%), tolbutamide (C₁₂H₁₈N₂O₃S, purity 98%), enalapril maleate (C₂₀H₂₈N₂O₅·C₄H₄O₄, purity 99.8%), indapamide (C₁₆H₁₆ClN₃O₃S, purity 98.2%), nifedipine (C₁₇H₁₈N₂O₆, purity 99.8%), atorvastatin calcium (C₆₆H₆₈CaF₂N₄O₁₀·3H₂O, purity 94.9%), and reserpine (C₃₃H₄₀N₂O₉, purity > 99.9%) were purchased from national institutes for food and drug control (Beijing, China). Glyburide-d11 (C₂₃H₁₇ClD₁₁N₃O₅S, purity 98%) was purchased from Toronto Research Chemicals (Toronto, ON, Canada). Methanol (MeOH), acetonitrile (ACN), and methyl tert butyl ether (MTBE) were of HPLC grade and purchased from Fisher Scientific (Pittsburgh, PA, USA). Acetic acid was obtained from Guangzhou chemical reagent factory (Guangzhou, China). Ammonium acetate was purchased from Macklin (Shanghai, China). Ultrapure water was freshly prepared using the Milli-Q Advantage A10 system (Milli-Q Reference, Millipore, Boston, MA, USA). Blank rat plasma samples were harvested from healthy adult rats supplied by the Laboratory Animal Center of Sun Yat-sen University (Guangdong, China).