Synthesis of a RP/HILIC/IEC mixed-mode stationary phase from quaternization of silica bonded and aliphatic C8 groups containing mixed-core G2.0PAMAM dendrimers

For reducing operational complexity and expenses in HPLC laboratories, the development of versatile mixed-mode stationary phases into a single platform as an alternative to using two or even three single-mode columns are in high demand. PAMAM dendrimers, characterized by a tunable multifunctional globular structure, have attracted considerable attention for the development of stationary phases. This study, for the first time, reports the synthesis of a mixed-mode stationary phase using G 2.0 PAMAM (mixed-core). The synthetic protocol involved three steps: (i) synthesis of conventional EDA-core dendrimer up to generation 1.5; (ii) aminolysis of resulting G 1.5 PAMAM with 1,8-diaminooctane (1,8-DAO) to obtain mixed-core G 2.0 PAMAM having aliphatic C8 groups; and (iii) its grafting to silica base followed by quaternization using glycidol. The synthesis and fabrication of this stationary phase was validated through NMR, FTIR, BET, TGA, zeta potential, and elemental analysis. The retention mechanism of the stationary phase was investigated by varying the chromatographic conditions and quantum chemistry calculations. The successful separation of a wide range of substances, including alkylbenzenes, polycyclic aromatic hydrocarbons, phenols, nucleosides and bases, organic acids, and inorganic anions on the newly developed column not only revealed its versatility for RPLC/HILIC/IEC mixed-mode chromatography, but also showed certain superiority to commercial columns. Moreover, the column exhibited excellent compatibility to 100% aqueous mobile phase–a step towards green chemistry principles for HPLC separations. The results implied that the proposed stationary phase holds significant prospects for separation of other classes of compounds, particularly the ones with certain degree of polarity.