Potassium dihydrogen phosphate

For extraction and isolation, n-hexane and methanol were purchased from Kanto Chemicals (Osaka, Japan) and Kieselgel 60 F₂₅₄ purchased from Merck (Darmstadt, Germany) used for thin-layer chromatography (TLC). Deuteromethanol (CD₃OD) (Kanto Chemical, Osaka, Japan) was used for preparing NMR samples. The mobile phase used for HPLC and UPLC were acetonitrile (Kanto Chemical, Osaka, Japan) and formic acid (FUJIFILM Wako Pure Chemical, Japan). L-cysteine methyl ester hydrochloride and N, O-bis (trimethylsilyl) trifluoroacetamide (Tokyo Chemical Industry, Tokyo, Japan) and pyridine (Nacalai Tesque, Japan) were used for acid hydrolysis of GC-MS samples. Methanol purchased from Nacalai Tesque used for polarimeter, UV and quantification analysis. Kaempferol as standard for quantification was purchased from Tokyo Chemical Industry (Japan) For IR analysis, KBr was purchased from FUJIFILM Wako Pure Chemical. For the α-glucosidase inhibitory activity assay, α-glucosidase from Saccharomyces cerevisiae was purchased from Sigma Aldrich (Germany). Acarbose hydrate, as the positive control, was obtained from Tokyo Chemical Industry (Tokyo, Japan). Phosphate buffer was prepared by mixing dipotassium hydrogen phosphate and potassium dihydrogen phosphate purchased from FUJIFILM Wako Pure Chemical. Dimethyl sulfoxide, sodium chloride, and sodium carbonate were purchased from Nacalai Tesque.

L-lactic acid (CAS: 79-3344, 129-02666), sodium chloride (CAS: 7647-14-5, 195-15975), potassium dihydrogen phosphate (CAS: 7778-77-0,164-22635), disodium hydrogen phosphate (CAS: 7558-79-4, 042-30055), urea (CAS: 57-13-6, 215-00172), ethanol (CAS: 64-17-5, 057-00456), D-glucose (CAS: 50-99-7, 049-31165), L-valine (CAS: 72-18-4, 228-00082), L-leucine (CAS: 61-90-5, 124-00852), and ammonia (CAS: 1336-21-6, 013-17505) were all purchased from Wako, Japan. Lactate oxidase (LOD) from Aerococcus viridans (T-47, Asahi Kasei Pharma, Tokyo, Japan) was purchased from Asahi Kasei Pharma and was used to modify the electrode of the biosensor. Osmium-wired horseradish peroxidase (002096, Bioanalytical Systems, West Lafayette, IN, USA) was purchased from BAS Inc., Tokyo, Japan. Phosphate-buffered saline (PBS, pH 7.4, 50 mM (PO₄)) was prepared in the laboratory. Ultrapure water obtained from the water purification system (Direct-Q, Merck, Darmstadt, Germany) was used for the preparation of all aqueous solutions.

The pH was adjusted by adding disodium phosphate (10 mM, FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan) containing sodium chloride (137 mM, FUJIFILM Wako Pure Chemical Corporation) and potassium chloride (2.68 mM, KANTO CHEMICAL, Tokyo, Japan) to potassium dihydrogen phosphate (2.0 mM) containing sodium chloride (137 mM, FUJIFILM Wako Pure Chemical Corporation) and potassium chloride (2.68 mM, FUJIFILM Wako Pure Chemical Corporation).

Mepenzolate, PPE and HPLC-grade acetonitrile were obtained from Sigma-Aldrich (St. Louis, MO). Novo-Heparin for injection was from Mochida Pharmaceutical Co. (Tokyo, Japan). Chloral hydrate was from Nacalai Tesque (Kyoto, Japan). Diff-Quik was from the Sysmex Co (Kobe, Japan). Sodium 1-propanesulfonate was from Tokyo Kasei Chemical Co (Tokyo, Japan). The Amicon utra-0.5 centrifugal filter unit was purchased from Merck Millipore (Billerica, MA). Formalin neutral buffer solution, potassium dihydrogen phosphate and methylcellulose were from WAKO Pure Chemicals (Tokyo, Japan). Mayer's hematoxylin, 1% eosin alcohol solution and malinol were from MUTO Pure Chemicals (Tokyo, Japan). ICR mice (4–6 weeks old, male) were purchased from Charles River (Yokohama, Japan). The experiments and procedures described here were carried out in accordance with the Guide for the Care and Use of Laboratory Animals as adopted and promulgated by the National Institutes of Health, and were approved by the Animal Care Committee of Keio University.

Serotonin Creatinine Sulfate Monohydrate (serotonin) for the serotonin standard and isotope-labeled Serotonin Creatinine Sulfate Monohydrate (α, α, β, β-d₄, 98%, serotonin-d₄) for the internal standard (IS) were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan) and Otsuka Pharmaceutical Co., Ltd. (Tokyo, Japan), respectively. Each of these materials was dissolved in a water–methanol mixture (water/methanol=40/60%, v/v) to prepare a 1 mM stock solution, which was then diluted to prepare samples for method evaluation, quality controls, and calibration curves.
Dipotassium hydrogen phosphate and potassium dihydrogen phosphate were purchased from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan). Two aqueous solutions of the same concentration of Dipotassium hydrogen phosphate and potassium dihydrogen phosphate were mixed at a ratio of 6 : 4 to prepare a 10 mM phosphate buffer at pH 6.8. Acetonitrile, formic acid, and 25% ammonia water were purchased from FUJIFILM Wako Pure Chemical Corporation. A 7.5% ammonia solution (water/methanol=30/70%, v/v) was prepared by mixing 25% ammonia water and methanol at a ratio of 3 : 7.
We used spin centrifuge columns for the SPE. The cation exchange column, MonoSpin© CBA, was purchased from GL Science Inc. (Tokyo, Japan).

The Corydalis Tuber extract was analyzed for its berberine content using high-performance liquid chromatography (HPLC) according to a previous study’s method [54 (link)]. The analysis was performed on an Arc HPLC (Waters Corporation, Milford, MA, USA.) coupled with a 2998 photodiode array detector using a YMC-Triart C18 column (catalog number: TA12S05-2546WT; YMC Korea, Seongnam, Republic of Korea). The mobile phase was water–acetonitrile at 1:1 (v/v), with 3.4 g/L potassium dihydrogen phosphate (catalog number: 169-04245) and 1.7 g/L of sodium dihydrogen phosphate (catalog number: 169-04245), both purchased from Fujifilm Wako Pure Chemical Corporation, Osaka, Japan, and 1.7 g/L of sodium lauryl sulfate (catalog number: 1436, Duksan Pure Chemicals Co., Ltd., Ansan, Republic of Korea). The HPLC analysis was carried out under isocratic conditions with a flow rate of 1 mL/min and a column temperature of 40 °C. Berberine was identified at a wavelength of 345 nm; the total analysis time was 60 min.