Evaluation of Aluminium Complexation Reaction for Flavonoid Content Assay
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Evaluation of Aluminium Complexation Reaction for Flavonoid Content Assay Anna Pękal & Krystyna Pyrzynska
Received: 28 November 2013 / Accepted: 22 January 2014 # The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract Two widely applied spectrophotometric assays based on aluminium complex formation used for determination of total flavonoid content in food or medicinal plant samples were examined for several compounds from different classes of flavonoid family. The method which involves the measurement at 410–430 nm after addition of AlCl3 solution is selective only for flavonols and flavones luteolin. The procedure in the presence of NaNO2 in alkaline medium seems to be specific for rutin, luteolin and catechins, but also phenolic acids exhibit considerable absorbance at 510 nm. Application of both procedures to natural samples gave different order in terms of their flavonoid content. Thus, the expression “total flavonoid” content is not adequate as the results of both methods are dependent on the structure of the individual flavonoids present. Keywords Total flavonoid . Aluminium chloride reaction . Quantitative determination
Introduction The spectrophotometric assay based on aluminium complex formation is one of the most commonly used procedure for the so-called total flavonoid determination, as the content of these compounds is considered as an important parameter for evaluating food or medicinal plant samples. This method, proposed initially by Christ and Müller (1960) for the analysis of herbal materials, was latter several times modified. Careful research in literature indicated variation in experimental conditions upon application of Al-flavonoid complexation reaction. Table 1 shows a short overview of literature studies employing this A. Pękal : K. Pyrzynska (*) Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland e-mail: [email protected]
reaction for evaluation of “total flavonoid” content in different kinds of samples. Two widely applied procedures can be distinguished. In the first one, AlCl3 solution in the concentration range of 2–10 % (m/v) is added to a sample and can be applied in the presence of acid or acetate solution; in some cases, only methanol or water is added. Measurements were done after 2– 60 min of the addition of AlCl3 at 404–430 nm and different flavonols (quercetin, rutin, quercetrin, galangin) as well as flavan-3-ol catechin were used as the standard compounds for the expression of results. In the second often used procedure, complexation reaction is carried out in the presence of NaNO2 in alkaline medium, which was applied in the past for the determination of o-diphenols (Barnum 1977). The method is based on the nitration of any aromatic ring bearing a catechol group with its three or four positions unsubstituted or not sterically blocked. After addition of Al(III), a yellow solution of complex was formed, which then turned immediately to red after addition of NaOH, and the value of absorbance is measured at
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