Modular and conservative procedure for the quantification of amino functionalities bonded to solid porous matrices

Nowadays solid materials in which amino groups are linked to silica matrices through alkyl chains of different length (C18, C8, C4) are successfully employed in CO₂ capture and storage technologies, as well as in a variety of chromatographic applications. In particular, their use as stationary phases finds remarkable success in performing HILIC separations and, in general, in the effective resolution of important compound classes (e.g. mixtures of mono- or oligo-saccharides). In this study an original and operationally simple procedure designed to quantify the density of basic groups (typically amino groups) chemically bonded to the surface of porous solids, which also allows a full recovery of the analysed material, is presented. The method is based on the preventive acid-base reaction of the basic groups linked to the solid by 3,5-dinitrobenzoic acid (DNBA). The quantification of the basic functionalities is then performed by an UV-spectrophotometric retro-titration of the thus salified solid matrix (or, alternatively, by HPLC approach), resorting to a preventive either acid or basic displacement of DNBA from the matrix. The uncertainty of the density measurements is assessed by 13%.