Size fractionation and characterization of natural aquatic colloids and nanoparticles

Atomic force microscopy (AFM) was used to image and quantify natural nanoparticles (prefiltered < 25 nm) from three different freshwater sites (Vale Lake, Bailey Brook and Tern Rivers). Four fractions were analysed by AFM; the prefiltered fraction (< 25 nm) and three fractions collected after separation of this prefiltered sample by flow field-flow fractionation (FIFFF) which corresponds to material which has size ranges of < 4.2 nm, 4.2-15.8 nm and 15.8-32.4 nm, as determined by FIFFF theory. The large majority of materials in all samples appeared as < 3 nm nanoparticles, nearly spherical and rich in chromophores active at 254 rim, UV, which thus correspond to natural organic matter. However, nanoparticles were also imaged up to slightly more than 25 inn in size, indicating a slight disagreement in sizing between filtration and FIFFF. In addition, some particles in certain fractions were found to be covered with a thin film of less than 0.5-1.0 nm. Substantial differences between sites were observed. (c) 2007 Elsevier B.V. All rights reserved.