Natural sample fractionation by F1FFF-MALLS-TEM: Sample stabilization, preparation, pre-concentration and fractionation

Two flow field flow fractionation (FIFFF) systems: symmetrical (SFIFFF) and asymmetrical (ASFIFFF) were evaluated to fractionate river colloids. Samples stability during storage and colloids concentration are the main challenges limiting their fractionation and characterization by FIFFF. A pre-fractionation (<0.45 mu m) 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 SFIFFF and on channel concentration in the case of ASFIFFF were applied to minimize the required pre-concentration. Multi angle laser light scattering (MALLS), and transmission electron microscope (TEM) techniques are used to evaluate FIFFF fractionation behavior and the possible artifacts during fractionation process. This study demonstrates that, FIFFF-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 Cezerat and Chatillon. Furthermore, comparison of SFIFFF and ASFIFFF fractograms for the same sample shows small differences in particle size distributions. (c) 2005 Elsevier B.V. All rights reserved.