Contribution of capillary electrophoresis to an integrated vision of humic substances size and charge characterizations

Abstract

The physicochemical properties of three different humic substances (HS) are probed using capillary zone electrophoresis in alkaline carbonate buffers, pH 10. Special attention is drawn to the impact of the electrolyte ionic strength and counter-ion nature, chosen within the alkali-metal series, on HS electrophoretic mobility. Taylor-Aris dispersion analysis provides insights into the hydrodynamic radius (R(H)) distributions of HS. The smallest characterized entities are of nanometric dimensions, showing neither ionic strength- nor alkali-metal-induced aggregation. These results are compared with the entities evidenced in dynamic light scattering measurements, the size of which is two order of magnitude higher, ca. 100 nm. The extended Onsager model provides a reasonable description of measured electrophoretic mobilities in the ionic strength range 1-50 mM, thus allowing the estimation of limiting mobilities and ionic charge numbers for the different HS samples. An unexpected HS electrophoretic mobility increase (in absolute value) is observed in the order Li(+)<Na(+)<K(+)<Cs(+) and discussed either in terms of retarding forces or in terms of ion-ion interactions.

The Intrinsic Stability of Metal Ion Complexes with Nanoparticulate Fulvic Acids

“…15 min after mixing M and FA remained constant over several hours. This result is expected for the small, nonaggregating Suwannee River FA, at a pH below that at which metal ion hydrolysis occurs, and is in line with the fast ionic partition processes in charged nanoparticles (nano to microsecond scales). , …”

Eu(III)–Fulvic Acid Complexation: Evidence of Fulvic Acid Concentration Dependent Interactions by Time-Resolved Luminescence Spectroscopy

“…with ionic strength of the smallest entities of HS, including SRFA, has given contrasted results. 76,77 When d'Orlyé and Reiller 77 did not evidence a clear increase in R H with ionic strength at pH 10 in…”

Modelling metal–humic substances–surface systems: reasons for success, failure and possible routes for peace of mind

“…The interaction of HS with metal ions follows the Irving and Williams (1948) series Skinner, 1966, 1967;Kerndorff and Schnitzer, 1980): alkali-metal interactions are weak (van den Hoop et al, 1990;d'Orlyé and Reiller, 2012) and the strongest interaction is with M 4+ elements (Reiller, 2005;Reiller et al, 2008). The interaction is weakly selective between analogous metals (vide supra).…”

“…From a structural point of view, Wershaw (1986Wershaw ( , 1989Wershaw ( , 1993Wershaw ( , 1999 proposed that NOM was made up of aggregates of small molecules. As part of NOM, HS also contain aggregates of small molecules (Aiken and Malcolm, 1987;Chin et al, 1994;Plancque et al, 2001;Kujawinski et al, 2002b;These et al, 2004) and organic nanometre-scale entities (Bouby et al, 2002;Baalousha and Lead, 2007;d'Orlyé and Reiller, 2012) with a fractal organization (Österberg et al, 1995;Senesi et al, 1997;Rice et al, 1999), which can clump together to form larger aggregates (Pinheiro et al, 1996;Manning and Bennett, 2000;d'Orlyé and Reiller, 2012). The 'micelle-like' or 'membranelike' paradigm proposed by Wershaw (1986Wershaw ( , 1993Wershaw ( , 1999Wershaw ( , 2000 may initially appear too organized to reflect the inherent heterogeneity of NOM or HS, but the recognition of a degree of organisation in NOM aggregates undoubtedly stems from Wershaw's work.…”