Skin powder method

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The hide powder method is a conventional method described in the European Pharmacopoeia for determining the content of tannins in drugs .

The powdered drug is weighed exactly and extracted with boiling water . After filtering , the filtrate is divided. The first aliquot is mixed with skin powder (standardized, powdered skin) and incubated for 60 minutes: tannins adsorb on skin powder and can be separated off by subsequent filtration.

Sodium tungstate / phosphoric acid reagent is then added to both parts of the filtrate :
Polyphenols combine with phosphotungstic acid to form blue-colored poly tungstic acids. In the second aliquot, the total polyphenol content (tannins, flavonoids , phenol carboxylic acids, etc.) is determined. The tannins were removed from the first aliquot by adding hide powder, so that the tannin content can be calculated from the difference between total polyphenols minus the “blank value”.

The measurement is carried out photometrically at 760 nm against water as a compensation solution.