Quercetin Determination in Dietary Supplement and in Onion Peel Extracts using a Photoluminescent 3-mercatpopropionic acid (3MPA) CdTe Quantum Dots Analytical Probe

A method to quantify quercetin (QUE) was developed based on the quenching effect this flavonoid exerts on the photoluminescence of 3-mercaptopropioni acid (3MPA) CdTe quantum dots (QDs) in aqueous solution. The luminescence (460/527 nm) from 3MPA-CdTe QDs (at an estimated 1.5  10-7 mol L-1) produced a linear relationship (R2 0.990) between the luminescence quenched normalized signal in function of QUE concentration between 5.0  10-6 and 6.0  10-5 mol L-1. The proposed method was successfully used to quantify QUE in the presence of other flavonoids and vitamin C with a limit of detection of 3.2  10-6 mol L-1. The standard deviation at the 10-5 mol L-1 level of QUE was 2%. The effect of other flavonoids in QDs luminescence was evaluated and no interference was observed in the case of catechin and flavone (at concentrations as high as 5 times the one of QUE). Hisperitin, naringenin, kaempferol, and galangin showed no interferences at the same concentration of QUE. However, morin interfered when present even at the same concentration of QUE. Vitamin C interfered when present at a concentration higher than 10 times the one of QUE. The contents of QUE in manipulated formulation and food supplement capsules were determined by the proposed method and compared with results obtained by HPLC. Finally, quercetin determination with 3MPA-CdTe QDs was applied for the analysis of yellow and red onion extracts after thin-layer chromatography to enable selectivity towards QUE.