This step in polyphenol analysis may look simple, but the more simple methods you utilize the less accurate are the results. On the other hand, accurate methods must be mastered perfectly or the results could be even worse than with the simple methods.
After polyphenol identification the next typical step is its quantitation from the original plant tissue. There are multiple methods available for this purpose, but most of them suffer from being only able to estimate the concentration of the individual polyphenol. For this reason, before choosing the method for quantitation, one must know what one is trying to achieve.
We have a range of methods for quantifying different types of polyphenols in plant tissue. In addition to the traditional methods that are able to estimate total polyphenol concentrations we more typically utilize accurate methods such ultra-performance liquid chromatography attached to a triple quadrupole mass spectrometer (UPLC-QQQ-MS/MS). By fully compound-specific multiple reaction monitoring (MRM) methods and by authentic standards isolated from plants, we are able to pursue as close to natural concentrations of polyphenols in a plant tissue as possible. At the same time we realize that it is simply impossible to achieve exactly matching quantitations with the quantity that was present in the living plant cell. Nevertheless, we all should aim at minimizing the changes made in tannin composition and concentration after harvesting the tissue.
Our flag publication in this front is the recent MS/MS method paper by Marica:
Engström, M.T.; Pälijärvi, M.; Fryganas, F.; Grabber, J.; Mueller-Harvey, I.; Salminen, J.-P. 2014. Rapid qualitative and quantitative analysis of proanthocyanidin oligomers and polymers by UPLC-MS/MS. J. Agric. Food Chem. 62(15): 3390–3399.