Improved Sample Treatment for the Determination of Flavonoids and Polyphenols in Sweet Potato Leaves by Ultra Performance Convergence Chromatography-tandem Mass Spectrometry

This work reports the development and application of a multi-compound analysis method for the determination of 17 flavonoids and polyphenols in sweet potato leaves. Samples were processed by microwave-enhanced accelerated solvent extraction under low pressure at 120 °C for 10 min. Salting-out homogeneous liquid-liquid extraction was used to remove water and water-soluble impurities from the extract before ultra performance convergence chromatography-tandem mass spectrometry analysis. By using the supercritical fluid (CO and methanol) as the mobile phase, the 17 components and the internal standard were well separated in 10 min without obvious matrix effect. Method validation was performed and good accuracy (relative error in the range of ±3.6%) and precision (inter- and intra-day relative standard deviations<10.9%) were obtained. The limits of detection were in the range of 0.1-0.6 ng ∙ mL. Recoveries were assessed at three concentration levels and acceptable mean values (76.1-101.5%) were found. This method has also been used to analyze ten different samples, and the average concentrations of components were determined in the range of 4.9-218.6 mg/100 g dry weight. The results showed the method could be helpful for the analysis of flavonoids and polyphenols in plant leaves.