3.3.1. Materials

The isolated 31 compounds including 24 flavonoids, and 7 phenolic acids were used for reference standards. Their purities were > 98%.

HPLC grade Acetonitrile (Thermo-fisher, Waltham, MA, USA), formic acid (Roe Scientific Inc., Newark, NJ, USA), and ultra-pure water prepared with a Milli-Q purification system (Millipore, MA, USA) were used for LC-MS analysis.

#### 3.3.2. Sample Preparation

#### Preparation of Standard Solutions

Standard test solutions of the above-mentioned standard references were prepared in MeOH at a final concentration of 1 μg/mL approximately. All stock solutions were stored at 4 ◦C in darkness and brought to room temperature before use.

### Preparation of the Aerial Parts of *A. mongolicum* Extract Test Solutions

*A. mongolicum* extract (AM) was prepared by using the same method as described in "Extraction and Isolation" section. The AM was dissolved with MeOH and filtered with 0.22 μm microporous membrane to get test stock solution at a final concentration of 30 mg/mL, which was stored at 4 ◦C in darkness and brought to room temperature before use.

#### 3.3.3. UHPLC

A Thermo UltiMate 3000 UHPLC instrument (Thermo, Waltham, MA) equipped with a quaternary pump, an autosampler was used to accomplish the analysis. Samples were separated on a Waters ACQUITY UPLC®HSS C18 (2.1 × 100 mm, 1.8 μm) using a mobile phase composed of H2O with 0.1% formic acid (A) and CH3CN with 0.1% formic acid (B) in the gradient program: 0–2 min, 9–10% B; 2–5 min, 10–17% B; 5–7 min, 17–20% B; 7–9 min, 20% B; 9–10 min, 20–86% B; 10–14 min, 86–100% B; 14–17 min, 100% B; An equilibration of 3 min was used between successive injections. The flow rate was 0.4 mL/min, and column temperature was 35 ◦C. An aliquot of 1 μL of each sample was injected for analysis.
