3.3. Method Validation of Quantitative Analysis
Linearity was examined with standard solutions. According to the antioxidant and antityrosinase assay (Table 2), nodifloretin (2), onopordin (4), cirsiliol (5), and eupafolin (7) are the major active compounds, but 5 was in a small amount and 2 was not well separated from the unknown side-peak in the tested sample; thus, only compounds 4 and7 were selected as the representative markers in this study. Each calibration curve contained five different concentrations and was performed in triplicate. The linearity for each compound was established by plotting the peak area (y) versus concentration (x) by the external standard method. The limits of detection (LOD) and quantification (LOQ) were determined at signal-to-noise ratios (S/N) of 3 and 10, respectively. The results are shown in Table 3.