High-performance liquid chromatography-DAD method fordetermination of flavonoids in some plants used as tea

The aim of this study is to develop an effective reverse phase-solid phase extraction (RPSPE)-diode array detection (DAD) method for the evaluation of flavonoid contents in infusions prepared from some herbal materials commonly used in traditional treatments. For this purpose, selected flavonoids such as myricetin, quercetin, rutin, luteolin, and apigenin were separated using a reverse phase C18 column (4.6 mm, 100 mm, 3 µm), a flow rate of 1.0 mL/min, and a DAD detector at 360 nm in a gradient elution system. The accuracy, precision, and repeatability of the method were demonstrated through validation studies. Furthermore, the amounts of phenolic acids present in the infusions were determined using a different reverse phase-SPE-DAD and gradient elution method, while the total phenolic content was determined spectrophotometrically using the Folin-Ciocalteu method. Additionally, the antioxidant activities of the infusions were determined through DPPH• and ABTS•+ radical assays. According to the ABTS•+ radical decolorization test, the highest antioxidant activity was observed in Hypericum perforatum and H. thymopsis infusions, which contained the highest amounts of chlorogenic acid, while Achillea millefolium infusions containing the highest amount of o-coumaric acid exhibited the highest activity. The lowest activity was observed in Lycium depressum fruit infusions. In the DPPH• radical superscript activity assay, the highest activity was detected in Hypericum perforatum (44.99 % inh.), H. thymopsis (31.89 % inh.), and Malabaila secacul fruit and herb (MSM and MSH, 35.32-38.81% inh, respectively) infusions.