An innovative method for quantification of basic sites linked on solid matrices

Recently, solid porous matrices functionalized with amino groups have found wide use in the field of CO2 capture and storage technologies [1] as well as in separation science for chromatographic applications. In fact, they are profitably used as stationary phases for HILIC (Hydrophilic Interaction Liquid Chromatography) separations [2], which allow the effective resolution of interesting compound classes (e.g. mixtures of mono- or oligo-saccharides). In this study, we developed a new method to quantify the density of basic sites linked on solid matrices (in particular, amino groups). Thanks to the mild operating conditions required by the method, this can also be used to quantify basic sites of matrices already packed in HPLC columns. The procedure is fast and easy to be used, and not destructive towards the analyzed material. The approach is based on the preventive salification of the basic groups linked to the solid by reaction with 3,5-dinitrobenzoic acid (DNBA), and for this reason from now on it will be denoted as DNBA-M. Quantification of the basic functionalities is then performed by an UVspectrophotometric retro-titration of the salified solid matrix resorting to a preventive either acid or basic displacement of DNBA from the solid material. Alternatively, the displaced DNBA can be quantified by reverse phase HPLC determination. For the development of this method they were employed six samples of derivatized silica, symbolized as AD-CSn, with n ranging from 1 to 6. Consequently, by means of the DNBA-M approach, for each of them it was quantified the relevant Amino Groups Density, AGD.