A Comparative Study of Diamine-Modified and Amine-Modified Silica Nanoparticles as Pseudo-Stationary Phases for CE Separation

The use of silica nanoparticles with surface modification in different applications is a topic of growing interest. This article provides a systematic comparison of diamine-modified and amine-modified silica nanoparticles as pseudo-stationary phases (PSPs) in capillary electrophoresis. The different electrophoretic behavior of these PSPs was evaluated by analysis of four auxins, indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 2,4-dichlorophenoxyacetic acid (dCPAA), and 2-(1-naphthyl)acetic acid (NAA). As expected, fast separation of the auxins was achieved, because they migrate in the same direction as the electro-osmotic flow under the optimum experimental conditions. However, the two nanoparticles had different selectivity and efficiency in the separation of the auxins, which could be related to the primary and secondary amines in their structures. The results indicated that even slight structural changes of the functional groups of the nanoparticles have pronounced effect on the interactions between the pseudo-stationary phase and the analytes.