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 conformational changes in humic acids induced by organic acids is reviewed. Particular attention is given td an evaluation of the role of non-size exclusion 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 been proven by experimental results from SEC-fractionation of HS in the absence of organic acids, and this has revealed similar interactions between the HS and the gel. The preference here is for the theory of non-size exclusion effects based on considerations of HS as natural polyelectrolytes.