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:
1. Flavonoids. Chemistry, Biochemistry and
Applications. Eds: O.M.Andersen, K.R.Markham.
N.Y.: CRR Taylor & Francis, 2005. 1237 p.
2. Battino R., Rettich T.R., Tominaga T. // J.
Phys. Chem. Ref. Data. 1983. V. 12.
2. P. 163178.
3. Vesilind P.A., Morgan S.M. Introduction
to Environmental Engineering. 2nd Edn. Boston:
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Onyang H. // J. Chem. Soc. Perkin Trans, 1998.
2. P. 1385-1390.
5.
.,
.,
.,
.,
. //
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. 2008. . 78. 9. . 1449-1456.
6. Brown S.B., Rajananda V., Holroyd J.A.,
Evans E.G.V. // Biochem. J. 1982. V. 205. P. 239244.
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Makarova S.V., Vitenberg A.G., Dobryakov
Yu.G., Utsal V.A. // Molecules. 2007. V. 12.
3.
P. 654-672.
8. Dubber M.-J. Application of CE, HPLC,
LC-MS-MS for the analysis and quality control of
Ginkgo Biloba dosage forms. Thesis. Rhodes University,
Greece,
2005.
.
:
http://eprints.ru.ac.za/294/01/MJ_Dubber_PhD.pdf
ON THE REASONS AND REMOVAL OF IRREPRODUCIBILITY OF DISSOCIATION
CONSTANTS OF QUERCETIN
Zenkevich I.G., Gushchina S.V.
Saint-Petersburg state university, faculty of chemistry
Dissociation constants (pKa) of one of the most spread natural flavornoids – quercetin –
are characterized by high irreproducibility. The principal reason of that seems to be easy oxidation of this compound by air oxygen during titration. The modified procedure of standard potentiometric titration is proposed to prevent such oxidation. It implies the bubbling of inert gas (niI
trogen) through titrated solution contained small additives of non-ionic detergent. Resulted
value (6.62 0.04) means that quercetin and, possibly, other flavonols at pH 7 (in neutral solutions) are dissociated in strong extent.
Keywords: Quercetin, dissociation constant, irreproducibility, preventing of oxidation,
modified potentiometric titration