DEVELOPMENT OF METHODS FOR QUANTITATIVE DETERMINATION OF TANNINS IN THE ROOTS OF RHEUM PALMATUM
In the present work are discussed the actual aspects of the development of methods of standardization of Rheum palmatum roots. Tannins are the second dominant group of biologically active substances in the roots of Rheum palmatum. The existing method of determining tannins in the roots of Rheum palmatum, presented in the FS.2.5.0092.18 State Pharmacopoeia of the Russian Federation XIV edition, provides for the use of methods of direct permanganatometric titration calculated on tannin with visual detection of the equivalence point in the form of the formation of golden-yellow staining due to the reaction of the first drop of excess potassium permanganate with indigocarmine, quite time-consuming and inaccurate. New approaches of quantitative analysis of tannins content in the roots of Rheum palmatum, consisting in the use of spectrophotometry method at an analytical wavelength of 282±2 nm calculated on catechin, are proposed. In order to maximize the extraction of tannins from the raw materials of Rheum palmatum were selected optimal conditions - water, the ratio of raw materials - extractant 1 to 50, extraction time in a boiling water bath - 15 minutes. UV spectra of solutions of water extracts from raw materials were studied using Unico 2800 spectrophotometer. The use of catechin, which gives a maximum absorption at a wavelength of about 282±2 nm, as a standard is the most optimal, since it is one of the dominant substances and is common in various other medicinal plants containing tannins as the main group of biologically active compounds, and, therefore, allows the data obtained to be used to compare the content of tannins in various medicinal plants. The content of tannins in roots the of Rheum palmatum under selected conditions of maximum extraction is 21.74%. The results of statistical processing of the experiments indicate that the error of a single determination of tannins in the roots of Rheum palmatum ±7.40%.The proposed method is simple, accessible and does not require the use of a large number of reagents.