Study of behavior of carboxylic magnetite core shell nanoparticles on a pH boundary

•Electrophoretic behavior of carboxylic nanoparticles on pH boundary was determined.•More than 10-fold preconcentration of nanoparticles on pH boundary was observed.•The preconcentration was attributed to the modification of surface and dispersion.•The behavior on pH boundary can hamper other studies of NPs as interactions.

During the last years, several authors have focused on the characterization of the size and charge of the nanoparticles by capillary electrophoresis. However, considering that nanoparticles are generally suspended in a solvent different from those commonly used as background electrolytes (BGE), an appropriate characterization of the behavior of the nanoparticles in the sample-BGE interface is required, as this might affect the overall electrophoretic behavior of the nanoparticles. In the present work, we address the evaluation of the behavior of COOH-coated maghemite nanoparticles in the vicinity of a pH boundary. To do so, different suspensions of nanoparticles prepared in acid media were injected into a borate/NaOH pH 9.5 BGE. The formation and evolution of boundaries in the sample-BGE interface in such systems was modeled by computer simulation. A systematic evaluation of the effect that parameters such as the co-ion, the sample pH or the injection time have on the electrophoretic behavior of the nanoparticles was carried out.