Linarin

6,8-Dimethoxycoumarin, tomentin, and diosmetin were isolated from L. chinensis by column chromatography and used as reference standards. Their structures were confirmed by nuclear magnetic resonance (NMR) [46 (link),47 ,48 (link)], and their purities by HPLC (≥98.0%). Other reference standards, namely, diosmin (≥98.0%) and linarin (≥98.0%), were purchased from ChemFaces Biochemical Co., Ltd. (Wuhan, China). HPLC-grade water, acetonitrile, and methanol were purchased from Honeywell Burdick and Jackson (Muskegon, MI, USA). Formic acid was from DAEJUNG Chemicals & Metals Co., Ltd. (Siheung-si, Korea).

CZE was dissolved in distilled 50% ethanol and then analyzed using a high-performance liquid chromatography (HPLC) system (Agilent 1260, Santa Clara, CA, USA). CZE was separated using Phenomenex kintex column C18 (4.6mm × 250 mm, 5μm) at a flow rate of 1.0 mL/min. To detect chromatogram, the mobile phase was composed of 0.025M KH2PO4 (pH 3.0: phosphoric acid) in water (solution A) and 100% acetonitrile (solution B), gradient 0–12 min (15–25% B), 12-20 min (25–41% B), 20–30 min (41–90% B), and then equilibrated with 15% B for 5 min. Standard compounds for HPLC analysis were used: chlorogenic acid (Cat. No.: 0050-05-90, purity: 96.67%, HWI Group), isochlorogenic acid A (Cat. No.: BP0056, purity: 98.0%, Chengdu Biopurity Phytochemicals), isochlorogenic acid B (Cat. No.: BP0055, purity: 98.0%, Chengdu Biopurity Phytochemicals), isochlorogenic acid C (Cat. No.: CFN90354, purity: 98%, Chemfaces), linarin (Cat. No.: BP0115, purity: 97.63%, Chengdu Biopurity Phytochemicals).