Online stacking of carboxylated magnetite core-shell nanoparticles in capillary electrophoresis

The stacking effect on carboxylated magnetite core-shell nanoparticles using sodium borate buffer pH 9.5 as the background electrolyte is presented. The ionic strength of the background electrolyte ranged from 5 to 100 mM, and the ionic strength of a sample zone ranged from 5 to 100 mM. Moreover, water was used as the sample dispersant. Both stacking and de-stacking effects were observed when conductivities of the sample zone and the background electrolyte differed. An explanation of carboxylated magnetic core-shell nanoparticles behavior was suggested based on the Derjaguin-Landau-Verwey-Overbeek theory supposing that the aggregation point is defined by the energetic barrier as the sum of energies given by electrostatic interactions and Van der Waals interactions. Moreover, the stacking conditions were applied for the evaluation of the lowest detectable dilution of magnetic nanoparticles. The carboxylated magnetic nanoparticles were dispersed in 10 mM borate/NaOH pH 9.5 and injected for 60 s to the background electrolyte composed of 100 mM borate/NaOH pH 9.5 that allowed the detection of 100-fold diluted nanoparticles.