Metal speciation measurement by diffusive gradients in thin films technique with different binding phases

Abstract

Since its invention in the mid-1990s, the diffusive gradients in thin films (DGT) technique has rapidly become one of the most promising in situ sampling techniques for trace metal measurement in natural waters. We investigated here the possibility of using DGT devices with different binding phases to det. different DGT labile fractions of Cd and Cu in lab. solns. and in natural waters. Several binding phases were studied, including conventional Chelex 100 resin imbedded polyacrylamide hydrogel (Chelex) and several recently developed binding phases, poly(acrylamide-co-acrylic acid) (PAM-PAA) gel, poly(acrylamidoglycolic acid-co-acrylamide) (PAAG-PAM) gel, Whatman P81 cellulose phosphate ion-exchange membrane (P81), and poly(4-styrenesulfonate) (PSS) aq. soln. Lab. testing in metal solns. spiked with EDTA or humic acid suggested that all the DGT devices measured only free metal ions and inorg. metal complexes. Upon field testing at both freshwater and seawater sites it was found that the DGT labile metal concns. measured by different binding phases can be significantly different, suggesting that the DGT labile metal fractions were dependent on binding strength of the binding phase. By designing binding phases that can compete with different natural water complexing ligands to varying extents, it is possible to use these different DGT devices to measure metal speciation in natural waters.