K2hpo4

The roots of AB were collected in Jiaozuo City, Henan Province in November 2020 (batch number: 20201114) and authenticated by Professor Ping Wang. Voucher specimens of the herb was deposited in the Moganshan campus of Zhejiang University of Technology. D₂O (99.9% D) was purchased from Sigma Co. (Darmstadt, Germany). K₂HPO₄ and NaH₂PO₄ were obtained from Xilong Chemical Co (Huanggu County, Shenyang, China). Phosphate buffer solution (pH 7.4) was prepared by dissolving 50 mM K₂HPO₄/NaH₂PO₄ in the D₂O. Standard substances, including L-valine, L-serine, L-proline, d-mannose, L-alanine, L-cysteine, L-leucine, L-lysine, L-threonine, L-aspartate, L-phenylalanine, and palmitic acid were obtained from Shanghai Ryon Biological Technology Co (Qingpu County, Shanghai, China). Citrate, succinic acid, glycine, glucose, cholesterol, and stearate and were purchased from Sinopharm Chemical Reagent Co (Jingan County, Shanghai, China).

D₂O (99.9% D) was purchased from Sigma-Aldrich (St. Louis, MO). K₂HPO₄ and NaH₂PO₄ were purchased from Xilong Chemical Co. Ltd. (Guangdong, China). Phosphate buffer solution (pH 7.4) was prepared by 50 mM K₂HPO₄/NaH₂PO₄ in the D₂O.

First, 4.00 g of the purified powder samples with a D50 of 10.06 μm, and 200 mL of the aqueous solution deionized water (blank sample), 40 mM oxalic acid (C₂H₂O₄·2H₂O, AR, Fuchen Chemical Reagents Factory, Tianjin, China), and 40 mM citric acid (C₆H₈O₇·H₂O, AR, Fuchen Chemical Reagents Factory, Tianjin, China) or composite acids (20 mM oxalic acid and 20 mM citric acid) was added to a 250 mL polypropylene bottle. The solution was adjusted to pH 4 using 0.05 M K₂HPO₄ (Xilong Science Co., Ltd., Shantou, China) and 0.05 M HCl (Xilong Science Co., Ltd., Shantou, China). The 2 mL chloroform had been added to each bottle. The mixtures were stirred at the speed of 500 r/min for 6 min. Then, each bottle was sealed and fully immersed in a thermostatic water bath at 25 °C. At regular intervals, the samples were stirred at the speed of 500 r/min for 1 min, then centrifuged and filtered through 0.45 μm nylon filters. The liquid phase was collected for later use. The solid phase in the centrifuge tube was washed several times with de-ionized water until the electrical conductivity of the dispersion decreased to 20 μScm⁻¹. Finally, the filter was dried and stored for later use.