Ligand exchange of hydrophilic molecules on the surface of hydrophobic iron oxide nanoparticles produced via thermal decomposition of chelated iron precursors is a common method for producing aqueous suspensions of particles for biomedical applications. Despite the wide use, relatively little is understood about the efficiency of ligand exchange on the surface of iron oxide nanoparticles and how much of the hydrophobic ligand is removed. To address this issue, we utilized a radiotracer technique to track the exchange of a radiolabeled (14)C-oleic acid ligand with hydrophilic ligands on the surface of magnetite nanoparticles. Iron oxide nanoparticles functionalized with (14)C-oleic acid were modified with poly(ethylene glycol) with terminal functional groups including, L-3,4-dihydroxyphenylalanine, a nitrated L-3,4-dihydroxyphenylalanine, carboxylic acid, a phosphonate, and an amine. Following ligand exchange, the nanoparticles and byproducts were analyzed using liquid scintillation counting and inductively coupled plasma mass spectroscopy. The labeled and unlabeled particles were further characterized by transmission electron microscopy and dynamic light scattering to determine particle size, hydrodynamic diameter, and zeta potential. The unlabeled particles were characterized via thermogravimetric analysis and vibrating sample magnetometry. Radioanalytical determination of the (14)C from (14)C-oleic acid was used to calculate the amount of oleic acid remaining on the surface of the particles after purification and ligand exchange. There was a significant loss of oleic acid on the surface of the particles after ligand exchange with amounts varying for the different functional binding groups on the poly(ethylene glycol). Nonetheless, all samples demonstrated some residual oleic acid associated with the particles. Quantification of the oleic acid remaining after ligand exchange reveals a binding hierarchy in which catechol derived anchor groups displace oleic acid on the surface of the nanoparticles better than the phosphonate, followed by the amine and carboxylic acid groups. Furthermore, the results show that these ligand exchange reactions do not necessarily occur to completion as is often assumed, thus leaving a residual amount of oleic acid on the surface of the particles. A thorough analysis of ligand exchange is required to develop nanoparticles that are suitable for their desired application.

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Surface water quality and the factors that influence it were investigated in a rural area that lies between an ice-pushed ridge and river backlands. The influences of soil type, land use and household wastewater on the concentrations of nutrients were studied during base-flow as well as peak-flow periods. Samples were taken in ditches and canals, more frequently as discharge increased. Average values of the base-flow quality in ditches were calculated per soil type and land use and for all measure points in the canals. The fluctuations of water quality were plotted and analyzed in concentration-time and concentration-discharge diagrams. The relative importance for the quality of total discharge in the main canal of the loads coming from several parts of the drainage basin, was investigated with a stepwise multiple variable regression analysis. During base-flow situations sources of nutrients are the intensively cultivated sandy soils. In addition the concentration of orthophosphate is increased by household wastewater. During peak-flows, potassium and nitrate run off from all soil types with all types of land use, resulting in high concentrations in the surface water, in spite of dilution by rainwater. It is concluded that for proper management, intensity of manuring and fertilizing should decrease, especially on sandy soils. Wastewater should be drained outside the basin, to lower the concentration of orthophosphate.

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