Tannic acid, reagent for

Tannic acid (reagent for albumin, alkaloids, and gelatin). 

Tannic add (reagent for albumin, alkaloids, and gelatin). Dissolve 10 g of tannic acid in 10 mL of alcohol and dilute with water to 100 mL. 

Of the three piperonyl compounds that have received considerable commercial attention as insecticides, a method of analysis is available only for piperonyl butoxide (41). This product gives a blue color on treatment with a reagent comprising tannic acid in a mixture of phosphoric and acetic acids. Satisfactory results can be obtained in the presence of small amounts of pyrethrins, but larger amounts tend to obscure the color. A modification of the method (21) which overcomes this difficulty is the removal of the pyrethrins by saponification with alcoholic sodium hydroxide prior to carrying out the test. 

The total phenolic content of plant extracts is usually determined by colorimetric method using Folin Ciocalteu reagent. This method entails oxidation of the phenolate ion coupled to the reduction of the phosphotungstic-phosphomolybdic reagent [6, 83, 84]. The chromophore produced is a blue phosphotungstic-phosphomolybdic complex which has a maximum absorption in the region of 750 nm [22, 85]. The total phenolic content is expressed as the number of equivalents of gallic acid, tannic acid, or caffeic acid used for the calibration curves. 

Soluble proteins may usually be precipitated by a variety of reagents, and many of them may be coagulated by heating. Some of the common salts, like ammonium sulfate, sodium sulfate, sodium chloride, etc., serve for salting out of many of these members in the unaltered condition, while certain acids (picric, tannic, phosphotungstic, phosphomolybdic, etc.) serve for their removal as insoluble salts. 

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