Dear prior to isolate tannin and gallic acid, prefer 70 % MeOH for extraction, followed by elusion with Water in MCI column. If MCI is not available then go for fractionation in water and chloroform. All the tannin and gallic acid will be diffused in water fraction
Do tlc of water fraction and spray it with FeCl3 eventually you get black or blue band in bottom of tlc in chloroform:methanol: water 6:4:1
Please see these posters:
https://www.teledynelabs.com/en-us/resources/Documents/Posters/Purification-of-Phenolic-Flavonoids-with-FC-Poster.pdf
https://www.teledynelabs.com/en-us/resources/Documents/Posters/Purification-of-Phenolic-Compounds-Using-a-Combination-of-Flash-and-Preparative-Chromatography.pdf
The first one describes isolating the phenolic compounds, including tannins, with an ion exchange column. The second one describes purification of different tannin types using polyamide and reverse phase. The reverse phase chromatograms are still very complex, so an intermediate step such as Sephadex LH-20, would be helpful before the reverse phase runs.
The collagen fiber adsorption material is prepared by formaldehyde cross-linking reaction. This material has obvious competitive adsorption capacity and adsorption selectivity for tannin. Experiments show that under experimental conditions, the removal rate of tannin can reach more than 97%, while the adsorption rate of effective ingredients is very low.