Low Colloid Concentrations Research Articles

Optimisation of on-channel preconcentration in flow field-flow fractionation for the determination of size distributions of low molecular weight colloidal material in natural waters

Flow FFF with UV detection has been used to determine the size distributions of colloidal material in natural waters. The method has been optimised with respect to flow rates, buffer composition and membrane type. The use of an on-channel preconcentration (focusing) technique allows very low colloid concentrations to be fractionated. The preconcentration process gives close to quantitative recovery with a detection limit equivalent to 9 μmol l −1 DOC for a 1.74 ml sample.

Zero-Valent Iron Colloid Emplacement in Sand Columns

Studies were conducted to evaluate a novel approach of emplacing chemically reactive barriers composed of zero-valent iron (Fe0) by injecting suspensions of colloidal-size Fe0 particles into porous media. The specific objective of this study was to evaluate the effect of influent colloid concentration, rate, and volume of colloidal suspensions on Fe0 colloid emplacement in sand columns. Relatively even distributions of Fe0 throughout a sand column were obtained at low influent colloid concentrations and high injection rates. As the concentration of influent suspension was increased, a point was reached beyond which a significant increase in the filtration of Fe0 particles near the front of the column was observed. This point was also found to occur at lower influent colloid concentrations as the injection rate was decreased, i.e., there was an interactive effect of influent colloid concentration and injection rate on the extent of filtration that occurred near the front of the column. As the volume of the colloidal suspension injected into the column was increased, the distribution of Fe0 colloids within the column became increasingly even.

The hydraulic conductivity of the rat proximal tubular wall determined with colloidal solutions.

The hydraulic conductivity of the rat proximal tubular wall was determined using colloidal solutions perfused in short (50--200 mum) (SMP) or long (90--200 mum) (LMP) proximal tubular segments. In SMP human serum albumin (HSA) or polyvinylpyrrolidone (PVP) was added to raffinose solutions. A Lp of 0.019 nl-min-1-mm-1-mm Hg-1 was found when high colloid concentrations were used while values of 0.055--0.092 were found when low colloid concentrations were used. In other experiments, the Lp was determined by perfusing short tubular segments with pure raffinose solutions. A value of 0.015 nl-min-1-mm-1-mm Hg-1 was found. This is twice the value found when raffinose solutions were perfused through long tubular segments and it is concluded that the short microperfusion technique overestimates Lp with a factor of two. When microperfusions of long tubular segments were conducted, PVP was added to an equilibrium solution consisting of NaCl (110 mM) and raffinose (80 mM). Lp was found to be 0.018--0.021 when high colloid concentrations were used, while a value of 0.029 was found when a low colloid concentration was used. As found in both SMP and LMP a decrease in Lp's with increasing colloid concentrations indicates that a significant influence of radial concentration differences is highly probable. It is therefore suggested that the highest Lp derived when using the lowest colloid concentrations represents the best estimate. With this Lp value (0.03--0.05 nl-min-1-mm-1-mm Hg-1) and the existing transtubular hydrostatic and oncotic pressure difference it can be calculated that these passive forces might constitute the driving force for 1/3 of the fluid reabsorbed in the proximal tubule.