SPECTROPHOTOMETRIC DETERMINATION OF QUERCETIN AND SUM OF POLYPHENOLS BY USING 18-MOLYBDODIPHOSPHATE HETEROPOLY COMPLEX T.A. Denisenko†, L.P. Tsiganok†, A.B. Vishnikin†* * Corresponding author † Oles Honchar Dnipropetrovsk National University, Gagarina St., 72, 49010, Dnepropetrovsk, Email: vishnikin@hotmail.com Methods Objects Chem. Anal., Volume 9, No 3, 2014 p. 130-138 https://doi.org/10.17721/moca.2014.130-138
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Abstract

18-molybdodiphosphate heteropoly complex (18-MPC) with Dawson structure was proposed as reagent for the spectrophotometric determination of quercetin and sum of polyphenols. Reaction of 18-MPC with quercetin and polyphenols goes under milder conditions than by using Folin-Ciocalteu reagent. Full development of the color is observed at pH 7 and takes less than one minute by the condition that reagent concentration is increased to 0.01 mol/l. Molar absorptivity for quercetin was equal to 5.5·10⁴ L·mol^-1·cm^-1 at 820 nm that allowed to determine up to 10^-7 mol (l = 5 cm) of it. 18-MPC can be successfully applied to the evaluation of the content of polyphenol compounds in plant preparations. Comparison of the results of the analysis obtained with the proposed reagent correlate well with the results of aluminium chloride and Folin-Ciocalteu methods. In some instances, the last method gives overestimated results. Because at pH 11.4 many substances have an influence on the determination of polyphenols, including monophenols, reducing sugars, phenolic acids, aminoacids, and proteins. In contrast to aluminium chloride, 18-MPC can react with most of polyphenolic compounds that allows more reliably to evaluate their content in great number of the objects of the analysis.

Keywords: 18-molybdodiphosphate, heteropoly complex, Folin-Ciocalteu reagent, polyphenol compounds, quercetin, spectrophotometric determination