title: Characterization of aggregates of surface modified fullerenes by asymmetrical flow field-flow fractionation with multi-angle light scattering detection.
abstract: Fullerenes are carbon nanoparticles with widespread biomedical, commercial and industrial applications. Attributes such as their tendency to aggregate and aggregate size and shape impact their ability to be transported into and through the environment and living tissues. Knowledge of these properties is therefore valuable for their human and environmental risk assessment as well as to control their synthesis and manufacture. In this work, asymmetrical flow-field flow fractionation (AF4) coupled to multi-angle light scattering (MALS) was used for the first time to study the size distribution of surface modified fullerenes with both polyhydroxyl and carboxyl functional groups in aqueous solutions having different pH (6.5-11) and ionic strength values (0-200mM) of environmental relevance. Fractionation key parameters such as flow rates, flow programming, and membrane material were optimized for the selected fullerenes. The aggregation of the compounds studied appeared to be indifferent to changes in solution pH, but was affected by changes in the ionic strength. Polyhydroxy-fullerenes were found to be present mostly as 4nm aggregates in water without added salt, but showed more aggregation at high ionic strength, with an up to 10-fold increase in their mean hydrodynamic radii (200mM), due to a decrease in the electrostatic repulsion between the nanoparticles. Carboxy-fullerenes showed a much stronger aggregation degree in water (50-100nm). Their average size and recoveries decreased with the increase in the salt concentration. This behavior can be due to enhanced adsorption of the large particles to the membrane at high ionic strength, because of their higher hydrophobicity and much larger particle sizes compared to polyhydroxy-fullerenes. The method performance was evaluated by calculating the run-to-run precision of the retention time (hydrodynamic radii), and the obtained RSD values were lower than 1%. MALS measurements showed aggregate sizes that were in good agreement with the AF4 data. A comparison of the scattering radii from the MALS with the hydrodynamic radii obtained from the retention times in AF4 indicated that the aggregate shapes are far from spherical. TEM images of the fullerenes in the dry state also showed branched and irregular clusters.
authors.affiliation: Analytical Chemistry Department, University of Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain. Electronic address: astefanei.alina@gmail.com.
authors.forename: Alina
authors.initials: A
authors.lastname: Astefanei
authors.affiliation: Analytical Chemistry Department-HIMS, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands.
authors.forename: Wim Th
authors.initials: WT
authors.lastname: Kok
authors.affiliation: KWR Watercycle Research Institute, Groningenhaven 7, PO Box 1072, 3430 BB Nieuwegein, The Netherlands.
authors.forename: Patrick
authors.initials: P
authors.lastname: Bäuerlein
authors.affiliation: Analytical Chemistry Department, University of Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain; Serra Hunter Fellow, Generalitat de Catalunya, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Núñez
authors.affiliation: Analytical Chemistry Department, University of Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Galceran
authors.affiliation: IBED, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam, The Netherlands.
authors.forename: Pim
authors.initials: P
authors.lastname: de Voogt
authors.affiliation: Analytical Chemistry Department-HIMS, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Schoenmakers
mesh_terms: D031521:Fractionation, Field Flow; D037741:Fullerenes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D053758:Nanoparticles; D009994:Osmolar Concentration; D010316:Particle Size; D012542:Scattering, Radiation; D012996:Solutions; D014867:Water
chemical_list: D037741:Fullerenes; D012996:Solutions; D014867:Water
keywords: Asymmetrical flow field-flow fractionation; Fullerene aggregates; Multi-angle light scattering