2.2. Analysis of Platycoside E and Platycodin D Using HPLC-ELSD

Standards of platycoside E and platycodin D were purchased from Cheongdu Biopurify Phytochemical Ltd. (Cheongdu, Sichuan, China). In order to perform quantitative analysis of platycoside E and platycodin D, 0.5 g of the extracted dry basis of Platycodon grandiflorum roots was dissolved in 40 mL of distilled water and defatted with diethyl ether in a separatory funnel. The aqueous layer was extracted with 40 mL of water-saturated n-butanol, three times. The n-butanol layer was evaporated at 50 °C, and the resulting residue was dissolved in methanol, and subjected to analysis. Platycoside E and platycodin D were identified by matching the retention time against the standards, and their contents were determined using calibration curves (Table S1). Platycoside E and platycodin D contents from PGE were analyzed using high-performance liquid chromatography (HPLC) with an evaporative light scattering detector (ELSD) (Waters Alliance 2695 HPLC system with 2424 ELSD, Waters, Milford, MA, USA), and a C-18 column (Luna C-18, Phenomenox, 250 × 4.6 mm, 5 μm, Torrance, CA, USA) was used for chromatography. A gradient of mobile phase was generated using (A) water and (B) acetonitrile as follows: 0–3 min, 21–21% B; 3–23 min, 21–23% B; 23–38 min, 23–24% B; 38–70 min, 24–100% B; 70–75 min, 100–100% B. The flow rate was 1.0 mL/min, the sample injection volume was 30 μL, and the column temperature was 40 °C. The ELSD conditions were as follows: Nebulizer temperature, 42 °C; drift tube temperature, 85 °C; and N₂ gas pressure, 50 psi.