The flavonoids in okra were quantified by external standard method. Quantification of the mixed reference solution was performed by Agilent 1200 Series HPLC/DAD using five point regression curves (R2 > 0.999) (Table 1 ). Chromatographic analysis refers to HPLC-MS/MS analysis. The working standard mixture was gained by dissolving all of the standard substances in 70% ethanol and diluting with ethanol to a series of appropriate concentrations and used to construct calibration curves. The concentration ranges for six analytes were unfolded in Table 2 . All the solutions were injected after being filtered by a 0.22 µm filter.
The accuracy of the above method was verified by a recovery test, which was performed using the above method by six (n = 6) replicate injections of spiked samples with a ratio of 1:1 between the standard content and the sample content and extracted. Precision/injection repeatability test was performed by six (n = 6) replicates injections of the mixed reference solution. The intra-day variations were injected in 1 day; the inter-day variations were injected after a 1 day interval. Variations were expressed as the percentage relative standard deviation (RSD%) of the replicates.
The accuracy of the above method was verified by a recovery test, which was performed using the above method by six (n = 6) replicate injections of spiked samples with a ratio of 1:1 between the standard content and the sample content and extracted. Precision/injection repeatability test was performed by six (n = 6) replicates injections of the mixed reference solution. The intra-day variations were injected in 1 day; the inter-day variations were injected after a 1 day interval. Variations were expressed as the percentage relative standard deviation (RSD%) of the replicates.