Size-based speciation of natural colloidal particles by flow field flow fractionation, inductively coupled plasma-mass spectroscopy, and transmission electron microscopy/X-ray energy dispersive spectroscopy: colloids-trace element interaction.

Flow field flow fractionation (FIFFF), inductively coupled plasma-mass spectroscopy (ICP-MS), and transmission electron microscopy (TEM) coupled to X-ray energy dispersive spectrometry (X-EDS) are used in series for the first time to characterize colloids. Results demonstrate the utility of FIFFF-ICP-MS-TEM/X-EDS to relate physical properties (size) of colloids to their chemical properties (chemical composition, surface chemical composition, and colloids-trace elements association). Results suggest that the major part of natural organic matter (NOM) is concentrated in the fraction < 0.01 microm (C2). Aluminum, iron, and manganese are the main colloidal components in the fraction 0.01-0.45 microm (C1). Aluminum occurs as aluminum oxides or aluminosilicates in the whole size range, while iron and manganese occur as individual oxyhydroxides in the size range < 0.20 microm. Within the C2 fraction, Al, Mn, Cu, and Ni elements are complexed to NOM (e.g., humic substances). Iron is complexed to NOM in some samples and probably free in other samples. Lead is totally free in all samples. Within the C1 fraction, Cu and Pb are mostly associated to Fe and Mn oxyhydroxides. Consequently, NOM with Fe and Mn oxyhydroxides are the main colloidal carriers of trace elements in the Loire watershed system.

Size fractionation and characterization of natural colloids by flow-field flow fractionation coupled to multi-angle laser light scattering.

Flow-field flow fractionation (FlFFF) coupled to multi-angle laser light scattering (MALLS) was evaluated for size and shape determination of standard spherical and arbitrarily shaped natural colloids. Different fitting methods for light scattering data retrieved from MALLS were evaluated to determine the particle size of spherical standards and natural colloids. In addition, FlFFF was optimized for best fractionation in connection to MALLS, minimal colloids-membrane interaction, and minimal sample losses. FlFFF, calibrated with standard particles, was used to determine hydrodynamic diameter, or radius (D(h) or R(h)), of the fractionated colloids, whereas the MALLS was used to determine root mean square radius of gyration (R(g)) for fractionated colloids. Combining both results, by calculating the R(g)/R(h) ratio, allows an estimation of colloid deviation from the shape of homogeneous sphere. Accordingly, this study demonstrates that, FlFFF-MALLS is a valuable technique for characterizing heterogeneous and arbitrarily shaped natural colloidal particles in terms of size and shape. To check the usefulness of FlFFF-MALLS in natural colloid studies, the technique was used to investigate the sedimentation behavior of extracted soil colloidal particles. Results illustrate that, in a silty till sample, carbonates function as cement between the colloidal particles, and consequently, change their sedimentation behavior. On the other hand, carbonate dissolution generates a more homogeneous colloidal sample.

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.