Gel-water partitioning of soil humics in diffusive gradient in thin film (DGT) analysis of their metal complexes

Metal complexes of humic and fulvic acids are ubiquitous in aqueous environmental media. In metal speciation analysis by DGT (diffusive gradient in thin film) with polyacrylamide hydrogels, soil humic acid species have been shown to significantly accumulate in the diffusive gel layer. As a result, the speciation of their metal complexes inside the gel is changed with respect to that in the sample medium. In low ionic strength samples, the effects of sorption of the charged humic species are compounded by Donnan partitioning. Here we lay out the basic features that govern the partition of humic species between gel and water, and discuss their effect on the properties of the DGT metal flux.