Phenols can be divided into monophenols (that is, phenols) and polyphenols (with multiple hydroxyl groups on the benzene ring). They exist in the form of neutral molecules and phenolic anions in aqueous solution at the same time, and the total polyphenols are the sum of polyphenols existing in the two forms (that is, phenolic substances do not contain phenol, and phenols are total phenols).
Polyphenol is not clear in what form it exists, so it can be understood differently. But generally speaking (when there is no special explanation), it is always understood as total polyphenols.
The role of total polyphenols? It is inappropriate to ask such a question. Polyphenols are common pollutants in water (mainly from wastewater discharge from printing and dyeing, paper making and other industries). By measuring the total polyphenols, we can know the pollution degree of these substances to water.