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CHARACTERIZATION OF SUB-MICRON AQUEOUS IRON(III) COLLOIDS FORMED IN THE PRESENCE OF PHOSPHATE BY SEDIMENTATION FIELD FLOW FRACTIONATION WITH MULTI-ANGLE LASER LIGHT SCATTERING DETECTION
Citation:
Magnuson*, M L., D A. Lytle*, C M. Frietch*, AND C A. Kelty*. CHARACTERIZATION OF SUB-MICRON AQUEOUS IRON(III) COLLOIDS FORMED IN THE PRESENCE OF PHOSPHATE BY SEDIMENTATION FIELD FLOW FRACTIONATION WITH MULTI-ANGLE LASER LIGHT SCATTERING DETECTION. Murray, R.W. (ed.), Analytical Chemistry. American Chemical Society, Washington, DC, 73(20), (2001).
Description:
Iron colloids play a major role in the water chemistry of natural watersheds and of engineered drinking water distribution systems. Phosphate is frequently added to distribution systems to control corrosion problems, so iron-phosphate colloids may form through reaction of iron in water pipes. In this study, sedimentation field flow fractionation (SedFFF) is coupled on-line with multi-angle laser light scattering (MALLS) detection to characterize these iron colloids formed following the oxygenation of iron(II) in the presence of phosphate. The MALLS-SedFFF data were used to calculate the hydrodynbamic diameter, density, and particle size distribution of these sub-micron colloids. The system was first verified with standard polystyrene beads, and the results compared well with certified values. Iron(III) colloids were formed in the presence of phosphate at a variety of pH conditions. The colloids' hydrodynamic diameters, which ranged from 218 plus or minus 3 nm (pH 7) to 208 plus or minus 4 nm (pH 10), did not change significantly with the 95% confidence limit. Colloid density did increase significantly from 1.12 plus or minus 0.01 g/mL (pH 7) to 1.36 plus or minus 0.02 g/mL (pH 10). Iron(III) colloids formed at pH 10 in the presence of phosphate were compared to iron(III) colloids formed without phosphate and also to iron(III) colloids formed with silicate. The iron(III) colloids formed without phosphate or silicate were 0.46 g/mL more dense than any other colloids and were >six times more narrowly distributed than the other colloids. The data suggest competitive incorporation of respective anions into the colloid during formation.