Environmental applications of flow field-flow fractionation (FIFFF)

Natural sample fractionation by FlFFF–MALLS–TEM: Sample stabilization, preparation, pre-concentration and fractionation

Two flow field flow fractionation (FlFFF) systems: symmetrical (SFlFFF) and asymmetrical (ASFlFFF) were evaluated to fractionate river colloids. Samples stability during storage and colloids concentration are the main challenges limiting their fractionation and characterization by FlFFF. A pre-fractionation (<0.45 microm) and addition of a bactericide such as NaN3 into river colloidal samples allowed obtaining stable samples without inducing any modification to their size. Stirred cell ultra-filtration allowed colloidal concentration enrichment of 25-folds. Scanning electron microscope (SEM) micrographs confirmed the gentle pre-concentration of river samples using the ultra-filtration stirred cell. Additionally, larger sample injection volume in the case of SFlFFF and on channel concentration in the case of ASFlFFF were applied to minimize the required pre-concentration. Multi angle laser light scattering (MALLS), and transmission electron microscope (TEM) techniques are used to evaluate FlFFF fractionation behavior and the possible artifacts during fractionation process. This study demonstrates that, FlFFF-MALLS-TEM coupling is a valuable method to fractionate and characterize colloids. Results prove an ideal fractionation behavior in case of Brugeilles sample and steric effect influencing the elution mode in case of Cézerat and Chatillon. Furthermore, comparison of SFlFFF and ASFlFFF fractograms for the same sample shows small differences in particle size distributions.

3D characterization of natural colloids by FlFFF-MALLS-TEM

Understanding the role of colloids in the environment needs a more complete characterization of their size and shape than the usually used hydrodynamic diameter. A novel methodology to determine three dimensional description of colloids has been successfully experimented in this work by coupling Flow-Field Flow Fractionation (FlFFF) to Multi Angle Laser Light Scattering (MALLS), and Transmission Electron Microscope (TEM). This methodology was evaluated for a soil colloidal sample. Results show that, the particles surface areas determined by FlFFF-MALLS-TEM, are 3-4 times greater than those calculated using the hydrodynamic diameter determined by FlFFF. Further, results indicated that, the surface area/volume values are 3-5 times greater than those calculated based on the hydrodynamic diameter. Therefore, a correction factor must be applied when the particle surface area is calculated from the hydrodynamic diameter determined by FlFFF.