Size exclusion chromatography of humic substances: Complexities of data interpretation attributable to non-size exclusion effects

The use of size exclusion chromatography (SEC) to support a theory of confo rmational changes in humic acids induced by organic acids is reviewed. Part icular attention is given td an evaluation of the role of non-size exclusio n effects in SEC experiments. In this review, results from SEC studies are interpreted in terms of electrostatic, salt, and specific sorption effects that influence the behavior of the HS on the gel. That interpretation has b een proven by experimental results from SEC-fractionation of HS in the abse nce of organic acids, and this has revealed similar interactions between th e HS and the gel. The preference here is for the theory of non-size exclusi on effects based on considerations of HS as natural polyelectrolytes.