Determination of key flavonoid aglycones by means of nano-LC for the analysis of dietary supplements and food matrices

A method for the analysis of flavonoids (myricetin, quercetin, naringenin, hesperitin, and kaempferol), with interesting bioactivity, has been developed and validated utilizing nano-LC technique. In order to find optimal conditions, capillary columns (75 m id x 10 cm) packed with different types of stationary phases, Kinetex (R) C18 core-shell (2.6 m particle size), Hydride-based RP-C18 (sub-2 m particle size), and LiChrospher (R) 100 RP-18 endcapped (5 m particle size) were evaluated. The method was validated using Hydride-based RP-C18 stationary phase, with sub-2 m particle size. A good chromatographic performance, expressed in terms of repeatability (RSD, in the range 1.63-4.68% for peak area), column-to-column reproducibility (RSD not higher than 8.01% for peak area), good linearity and sensitivity was obtained. In particular limit of detection values between 0.07 and 0.31 g/mL were achieved with on column focusing technique. The method was applied to the determination of studied flavonoids in dietary supplements as well as in food matrices. The amount of quercetin found in the first analyzed dietary supplement, was in agreement to the labeled content. In the other samples, where the content of flavonoids was not labeled, most of the studied flavonoids were determined in amounts somewhere comparable to those reported in literature.