Capillary isotachophoresis for separation of silver nanoparticles according to size

Capillary isotachophoresis (ITP) was used for the separation of Ag nanoparticles according to their size. For this purpose, ethanol-water dispersions of Ag nanoparticles stabilized by gelatin were prepared. The ITP separations were performed in a column-coupling system filled with two electrolytes with a pH of leading electrolytes of 7.1 (system I - LE: 10 mM HNO3, epsilon-aminocaproic acid, TE: 10 mM caproic acid) and 4.5 (system II - LE: 10 mM HNO3, imidazole, TE: 5 mM 2-(N-morpholino) ethanesulfonic acid). In both electrolyte systems the four main peak-mode zones of Ag nanoparticles migrating at zone boundaries were identified, however, the better separation was achieved by the system II. The Ag nanoparticle dispersions were also examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The zeta potential and thickness of gelatin double layers adsorbed on the nanoparticles were found to depend on pH. The TEM analysis revealed four size fractions of 4 nm, 10 nm, 16 nm and 22 nm, which correspond to the zones separated by ITP. Other migration zones of the electrolyte systems, such as impurities and/or products of the nanoparticle synthesis, served as spacers and separated the peak zones of the Ag nanoparticles.