Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Dynamic aspects of DGT as demonstrated by experiments with lanthanide complexes of a multidentate ligand.
AU - Aaberg-Garmo, Øyvind
AU - Lehto, Niklas J.
AU - Zhang, Hao
AU - Davison, William
AU - Royset, Oddvar
AU - Steinnes, Eiliv
PY - 2006/8/1
Y1 - 2006/8/1
N2 - Sampling of metals with the technique of diffusive gradients in thin-films (DGT) depends on the rates of diffusion and on the kinetics of interconversion of the species present. In this study the discrimination between metal complexes with different dissociation kinetics is investigated. Samplers with different thicknesses of diffusive and resin gels were deployed in solutions containing 10 g/L of each metal in the lanthanide (Ln) series (except Pm) and 2.0 × 10-6 M of the ligand quin2 at an ionic strength of 0.1 M (KNO3) and pH 7.0. Diffusion coefficients of Ln3+ ions and Ln-quin2 complexes were determined in a diffusion cell experiment. The equilibrium speciation of the metals was calculated from available stability constants. The sampling rate (mass/time) was highly dependent on the dissociation-rate constant of the complexes. For complexes with dissociation kinetics that appreciably limited the uptake, the sampling rate decreased significantly with increasing deployment times (12, 24, and 76 h) and was virtually independent of the thickness of the diffusive gel. Placing a layer of diffusive gel behind the resin did not influence the accumulation of Lns in the resin gel, but doubling the thickness of the layer containing resin increased the uptake, and more so for the Lns forming less labile complexes. The Lns forming more labile complexes were enriched in the outer layer of the resin, and there was a trend toward even distribution between the outer and deeper parts of the resin layer for the Lns forming less labile complexes. The measured DGT sampling rates (mass/time) were reasonably well predicted by a dynamic model that used independently determined kinetic constants. This new knowledge of how metal complexes behave in the sampling process paves the way for using DGT to obtain in situ kinetic information in natural waters.
AB - Sampling of metals with the technique of diffusive gradients in thin-films (DGT) depends on the rates of diffusion and on the kinetics of interconversion of the species present. In this study the discrimination between metal complexes with different dissociation kinetics is investigated. Samplers with different thicknesses of diffusive and resin gels were deployed in solutions containing 10 g/L of each metal in the lanthanide (Ln) series (except Pm) and 2.0 × 10-6 M of the ligand quin2 at an ionic strength of 0.1 M (KNO3) and pH 7.0. Diffusion coefficients of Ln3+ ions and Ln-quin2 complexes were determined in a diffusion cell experiment. The equilibrium speciation of the metals was calculated from available stability constants. The sampling rate (mass/time) was highly dependent on the dissociation-rate constant of the complexes. For complexes with dissociation kinetics that appreciably limited the uptake, the sampling rate decreased significantly with increasing deployment times (12, 24, and 76 h) and was virtually independent of the thickness of the diffusive gel. Placing a layer of diffusive gel behind the resin did not influence the accumulation of Lns in the resin gel, but doubling the thickness of the layer containing resin increased the uptake, and more so for the Lns forming less labile complexes. The Lns forming more labile complexes were enriched in the outer layer of the resin, and there was a trend toward even distribution between the outer and deeper parts of the resin layer for the Lns forming less labile complexes. The measured DGT sampling rates (mass/time) were reasonably well predicted by a dynamic model that used independently determined kinetic constants. This new knowledge of how metal complexes behave in the sampling process paves the way for using DGT to obtain in situ kinetic information in natural waters.
U2 - 10.1021/es060674v
DO - 10.1021/es060674v
M3 - Journal article
VL - 40
SP - 4754
EP - 4760
JO - Environmental Science and Technology
JF - Environmental Science and Technology
SN - 1520-5851
IS - 15
ER -