Comparison of Small- and Large-scale Ultrafiltration Systems for Organic Carbon and Metals in Freshwater at Low Concentration Factor

Abstract

Interdisciplinary studies on aquatic environments and cross-validation of laboratory vs. field results will likely increase the need for simultaneous use of large-and small-scale ultrafiltration systems. In this study, a comparison of two ultrafiltration systems differing in scale (PrepScale and PelliconXL, Millipore; membrane areas 0.54 m 2 and 0.005 m 2 , respectively), was made for the cut-offs 3 and 300 kDa. Large systems are useful for their high permeate throughput, while small systems are necessary when the amount of sample is limited. The ability of PrepScale and PelliconXL systems to provide comparable results for organic carbon fractionation was studied for polysaccharide solutions and natural freshwaters. In the latter, the colloidal proportions of different trace metals (V, Cr, Mn, Co, Ni, Cu, Sb, and U) were also determined. Although the colloidal proportions obtained with PelliconXL 3 kDa were sometimes slightly higher than with PrepScale 3 kDa (principally for DOC and U in natural waters), Mann-Whitney statistical test showed no significant difference in the overall fractionation properties of the two systems. Our observations show that reaching high concentration factors lead to a strong modification of colloids size distribution in the range 50-2,000 nm and thus low concentration factors are preferable to preserve the colloid integrity.

Total and methylmercury partitioning between colloids and true solution: From case studies in sediment overlying and porewaters to a generalized model

“…Stordal et al therefore suggested using CFs smaller than 10 for more consistent results in the partitioning of both Hg and DOC concentrations. Furthermore, Kottelat et al showed that increasing CFs resulted in the formation of large colloids in the retentate fraction of ultrafiltered waters, with possible consequences on element fractionation between colloids and true solution. In any case, our choice of CFs was actually dictated by the need to preserve a minimum sample volume for the subsequent chemical analysis of retentate fractions, especially for porewaters when the volume to ultrafilter was sometimes less than 100 mL (Supplemental Data, Table S1).…”

“…Tangential flow ultrafiltration was carried out using a Pellicon XL cartridge (regenerated cellulose, 3 kDa nominal cutoff). Before each use, the ultrafiltration membrane was thoroughly cleaned and preconditioned as described elsewhere . An ultrafiltration blank was performed before fractionation of each sample, using milliQ grade water to assess the background levels of THg and MMHg in the different laboratories (Supplemental Data, Table S2).…”

“…Most studies on Hg and MMHg partitioning between colloids and true solution used tangential flow ultrafiltration, so that the methodological limitations of the technique are well constrained . Diffusive gradients in thin films proved a valid alternative to 1 kDa tangential flow ultrafiltration for measuring the truly dissolved concentrations of Mn, Cd, and Zn in the Baltic Sea .…”

Field-flow fractionation: An efficient approach for matrix removal of soil extract for inductively coupled plasma optical emission spectrometry

“…Owing to its nature as a one step procedure, FlFFF/CFM can be coupled on-line between any sequential extraction unit and the ICP-OES system. The concept of the FlFFF/CFM is similar to that of the cross flow filtration generally used for colloid separation [26,27]. During cross flow matrix removal step, matrix free ions were filtered off through the membrane (1000) whereas the analyte-PEI complexes (25,000) retained in the FlFFF channel and traveled through the channel for ICP detection.…”

Natural occurring uranium nanoparticles and the implication in bioremediation of surface mine waters

“…A few studies have shown that colloids are quite mobile in the aquatic system (Guo et al, 2001;Kottelat et al, 2008;Nowack and Bucheli, 2007). This revelation bring a number of question on use of redox-transform from U(VI) to an insoluble U(IV) phase as a mean of immobilising uranium from the water pathway.…”