Dipotassium hydrogenphosphate

Ethanol, n-hexane, and ethyl acetate were purchased from Guangdong Guanghua Sci-Tech Co., Ltd. (Shantou, China). Potassium dihydrogen phosphate, dipotassium hydrogenphosphate, ascorbic acid (≥99.0%), trichloroacetic acid, Iron(III) chloride (FeCl₃), starch, and sodium hydroxide were purchased from Damao Chemical Reagent Factory (Tianjin, China). Phloroglucinol (≥99.0%), sodium carbonate, diammonium salt (ABTS), α-glucosidase, α-amylase, 3,5-dinitro salicylic acid, and potassium sodium tartrate were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). 4-nitrophenyl-α-D-glucopyranoside (PNPG), acarbose, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), and Folin-Ciocalteu reagent were purchased from Beijing Solarbio Technology Co., Ltd. (Beijing China). Potassium ferricyanide and potassium persulfate were purchased from Xilong Science Co., Ltd. (Shantou, China). Methanol was chromatographic grade and purchased from Concord Technology (Tianjin, China).

CGA, CGA-ME, and CGA-LT were purified by us using D101 macroporous resin, Sephadex LH-20 and ODS column chromatography, and preparative HPLC from the aqueous extract of FE; the compounds were identified by UV, IR, MS, and NMR technologies [14 (link)]. Their purities above 95% were determined by UPLC analysis. LC-grade acetonitrile was purchased from Sigma-Aldrich (St. Louis, MO, USA). LC-grade water was produced by a Milli-Q water purification system (Millipore, Massachusetts, MA, USA). Formic acid was bought from Meridian Medical Technologies (MREDA, New York, NY, USA). Phosphoric acid, disodium hydrogen phosphate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate were bought from DAMAO Chemical Reagent Factory (Tianjin, China).
The phosphate buffer solution at pH 2, 4, 6, and 8 was prepared according to the guidelines released by Chinese pharmacopoeia.