Determination of diffusion coefficients of nanoparticles and humic substances using scanning stripping chronopotentiometry (SSCP)

A methodology, based on a labile metal ion probe using stripping chronopotentiometry at scanned deposition potential (SSCP), is presented for the determination of the diffusion coefficients of nanoparticles and humic matter. The novel methodology was successfully applied to the determination of diffusion coefficients (and thus hydrodynamic diameters) of eight standard nanoparticles with radii ranging from 5 to 129 nm and two samples of colloidal humic substances with hydrodynamic radii of ca. 1 nm. Good agreement was found between the SSCP determinations and results obtained by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence correlation spectroscopy (FCS). The SSCP technique is critically analysed with respect to its use for the determination of diffusion coefficients of colloidal complexes.