The molecular size of natural organic matter (NOM) determined by diffusivimetry and seven other methods

The objectives of this work are to (1) determine the diffusion coefficients of natural organic matter (NOM) by diffusivimetry, (2) compare the results with diffusion coefficients determined by two other methods (fluorescence correlation spectroscopy (FCS) and dynamic adsorption experiments (DAM), (3) compare molecular weights derived from the diffusion coefficients to molecular weights determined by three different ultrafiltration experiments and high perfomance size exclusion chromatography (HPSEC). The diffusion coefficients determined in this work (stirred diffusion cell) are about 70% higher than that determined by DAM, and agree well with diffusion coefficients determined by FCS. Molecular weights determined by HPSEC are of the same magnitude as molecular weights derived from diffusion coefficients. Molecular weights determined by ultrafiltration vary considerably depending on the choice of membrane types. Membranes made of cellulose acetate generate results similar to results derived from diffusion coefficients. Membranes made of regenerated cellulose and polyether sulfone appear to retain too much of NOM, resulting in artificially high molecular weights.