Method of determination of the anionic charge density of a polymer

The present invention relates to a method for determining the anionic charge density of at least one polymer present in a sample, the following steps: - contacting and allow the interaction of at least one polymer present in the sample with a developing solution comprising lanthanide (III) ions, - exciting the sample at an excitation wavelength and detecting λexc, by time-resolved photoluminescence, a signal from the lanthanide (III) ion which interacts with the at least a polymer having an emission wavelength λem, and - determine the anionic charge density of the at least one sample of polymer by using the detected signal at the emission wavelength