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Analysis of gallic, digallic and trigallic acids in tannic acids by high-performance liquid chromatography

Inspired by the structure of tannic acid, first- to third-generation dendrimers containing two, four, and eight galloyl moieties were synthesized. Stability, antioxidant activity and collagen cross-linking activity of the natural product and its dendrimer analogues were compared. The experimental results indicate that polygalloyl dendrimers might be used as new lead compounds to improve the long-term healing characteristics of burn wounds.

A method for the identification and determination of tannic acid and its phenolic metabolites in biological fluids by high-performance liquid chromatography was developed. Tannic acid and four phenolic compounds, namely gallic acid, pyrogallol, 4-O-methylgallic acid and ellagic acid, were successfully extracted from the biological fluids by using ethyl acetate at acidic conditions. Gallic acid, pyrogallol and 4-O-methylgallic acid were found in the sheep urine, gallic acid, 4-O-methylgallic acid and ellagic acid in plasma, and gallic acid and ellagic acid in abomasal fluid after abomasal dosing of tannic acid. Tannic acid was found in the plasma apart from the abomasal fluid into which it was administered. The concentrations of tannic acid, gallic acid, pyrogallol, 4-O-methylgallic acid and ellagic acid in plasma, abomasal fluid and urine were measured. This method could be applied to measurement of other hydrolysable tannins and their phenolic metabolites in bioligical materials.

A high-performance liquid chromatographic (HPLC) method was developed for the quantitative comparison of various batches of tannic acid from the same manufacturer used to aid the binding of human chorionic gonadotropin to sheep erythrocytes in the manufacture of pregnancy testing kits. The tannic acids were separated by reversed-phase HPLC on a C₁₈ column using gradient elution with aqueous methanolic eluents at low pH. A portion of the chromatogram corresponding to the compounds involved in the tanninisation process was integrated and a linear relationship was established between this peak area and tannic acid concentration. The correlation coefficient was greater than 0.993 even in the absence of an internal standard. Tanning capacity was evaluated on the basis of the amount of tannic acid which remained following incubation with a known quantity of erythrocytes. The application of this procedure to three batches of tannic acid is demonstrated.

The complexation of several tannic acids (purified tannins) with soluble and insoluble proteins has been studied by high-performance liquid chromatography, Tannins are analysed in both the straight phase and the reversed-phase mode. Bovine serum albumin (BSA) and beer proteins were chromatographed in the size exclusion mode. Soluble proteins seem to complex preferentially with the higher molecular weight tannin polygalloyl glucose components, whereas insoluble standardized hide powder binds preferentially to lower molecular weight tannin components. The tanning capacity of different tannic acids can be expressed in milligrams of BSA bonded per milligram of tannin under standard conditions.