Microencapsulated L. plantarum IS-10506, which is a novel probiotic that is isolated from dadih (a traditional Indonesian fermented buffalo milk), was prepared as previously described.10 (link) Amlodipine (amlodipine besylate), the internal standard nortriptyline hydrochloride (NOR), and 4-chloro-7-nitrobenzofurazan (NBD-Cl) were purchased from Sigma Aldrich (Singapore). Methanol, acetonitrile, ethanol, sulfuric acid, hydrochloric acid, boric acid, and sodium hydroxide were purchased from Merck (Darmstadt, Germany). All reagents that were used were analytical grade, except for Methanol, which was high-performance liquid chromatography (HPLC) grade.
Stock solution of amlodipine was prepared by dissolving 10 mg of free base with 2 mL ethanol and diluting to 100 mL with water. A plasma standard with serial dilution of 2.5, 10, 40, 160, 640, and 1280 ng/mL was prepared to provide plasma calibration samples. NOR was prepared at a concentration of 100 µg/mL and diluted to obtain 50 ng/mL of working solution. NBD-Cl solution (0.08%, w/v) was freshly prepared in Methanol. Teorell and Stenhagen buffer solution13 was composed of phosphoric acid, citric acid, 0.1 M sodium hydroxide, and 0.1 M hydrochloric acid, and adjusted to a pH of 8.6.
Stock solution of amlodipine was prepared by dissolving 10 mg of free base with 2 mL ethanol and diluting to 100 mL with water. A plasma standard with serial dilution of 2.5, 10, 40, 160, 640, and 1280 ng/mL was prepared to provide plasma calibration samples. NOR was prepared at a concentration of 100 µg/mL and diluted to obtain 50 ng/mL of working solution. NBD-Cl solution (0.08%, w/v) was freshly prepared in Methanol. Teorell and Stenhagen buffer solution13 was composed of phosphoric acid, citric acid, 0.1 M sodium hydroxide, and 0.1 M hydrochloric acid, and adjusted to a pH of 8.6.