Author(s)

J.R. Lead & K.J. Mlkinson

Abstract

Measurement of diffusion coefficients of humic substances in a hydrogel and in water by fluorescence correlation spectroscopy 1 7 J.R. Lead and K. J. Wilkinson * Division of Environmental Health and Risk Management, University of Birmingham, U.K.. ^CABE, University of Geneva, Switzerland. Abstract Diffusion coefficients of three different humic substances (HS) were measured in both water and in agarose hydrogels. The three HS were standard Suwannee River humic and fulvic acid [1] and a peat humic acid [2]. Measurements were made by fluorescence correlation spectroscopy (PCS). In general, values of diffusion coefficients were in the range of 1.9-2.5 x 10"*° nf s"\ for all of the HS under all conditions (except a single peat derived HS at low pH). The small degree of polydispersity of the HS (observed both in the autocorrelation functions of the PCS and by atomic force microscopy, AFM) did not preclude the use of a single diffusion coefficient to ex

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