Revisited: DGT speciation analysis of metal–humic acid complexes

Abstract

Environmental context Humic acids and their metal complexes may be sorbed by the gel used in diffusive gradients in thin films (DGT) speciation analysis. Owing to the low mobility of the humic entities, the sorption process is very slow. As a consequence, the delay times involved in establishing a steady-state metal diffusion flux may be in the order of days. Abstract Soil humic acids and their metal complexes are sorbed by hydrogel phases such as those used in DGT analysis. The accumulation is spatially inhomogeneous: a thin film near the interface with the aqueous medium typically hosts ~10 times the concentration in the medium, whereas the bulk gel features an accumulation factor of ~2. Here we discuss the consequences of these sorption properties for the usual type of DGT experiment. It appears that the eventual steady-state metal flux is not affected, but the characteristic time of establishing truly steady-state diffusion conditions may be even longer than the common DGT deployment time of a few days.