With the previous calibration of free silanol groups, a correlation between the minima variation of the CT and the zero-crossover point of the δΨo 2 /δpH 2 can help in determining the contribution of silanol groups. For example, if the immobilization of carboxylic groups is done through classical amino-silanes (e.g. (3-Aminopropyl)triethoxysilane), a previous pH titration may be used to determine the number of free silanol groups.