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Diffusion coefficients of metals and metal complexes in hydrogels used in diffusive gradients in thin films [An article from: Analytica Chimica Acta]
Book Details
Author(s)S. Scally, W. Davison, H. Zhang
PublisherElsevier
ISBN / ASINB000RR70W2
ISBN-13978B000RR70W1
AvailabilityAvailable for download now
Sales Rank6,650,488
MarketplaceUnited States 🇺🇸
Description
This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in . The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.
Description:
Diffusion coefficients of metal ions and metal-ligand complexes in hydrogels were measured at ionic strengths of 0.1-100mmolL^-^1 using a diffusion cell. The three different types of hydrogel were all based on polyacrylamide and have been commonly used in the technique of diffusive gradients in thin films (DGT), where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. There was little difference in the diffusion coefficients of either Cu and Cd measured in gels with thicknesses of 0.4, 0.8 and 1.6mm, showing that any diffusion boundary layer in solution was negligibly small. The diffusion coefficients of Pb, Ni, Cu and Cd in simple inorganic solutions was independent of ionic strength (1-100mmolL^-^1), except at very low ionic strengths (0.1mmolL^-^1) where the value of D was 50% lower. This observation is consistent with the gel having a positive charge that creates a Donnan partitioning of cations at the gel surface. Diffusion coefficient of Pb complexes decreased with increasing size of the ligand, in the order of diglycolic acid (DGA), nitrilotriacetic acid (NTA), fulvic acid and humic acid. In freshwaters the contribution of fulvic acid species to measured DGT mass should be considered. No significant difference was found between the rate of diffusion of Cu and Cd through the mostly commonly used gel and the filter membrane at the face of the DGT device. Diffusion coefficients obtained using a gel with small pore size (restricted gel) plus filter membrane were higher than those obtained using the restricted gel alone. It may be necessary to modify the standard DGT equation for restricted gel deployments, to take into account the difference in diffusion between the gel and the filter membrane.
Description:
Diffusion coefficients of metal ions and metal-ligand complexes in hydrogels were measured at ionic strengths of 0.1-100mmolL^-^1 using a diffusion cell. The three different types of hydrogel were all based on polyacrylamide and have been commonly used in the technique of diffusive gradients in thin films (DGT), where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. There was little difference in the diffusion coefficients of either Cu and Cd measured in gels with thicknesses of 0.4, 0.8 and 1.6mm, showing that any diffusion boundary layer in solution was negligibly small. The diffusion coefficients of Pb, Ni, Cu and Cd in simple inorganic solutions was independent of ionic strength (1-100mmolL^-^1), except at very low ionic strengths (0.1mmolL^-^1) where the value of D was 50% lower. This observation is consistent with the gel having a positive charge that creates a Donnan partitioning of cations at the gel surface. Diffusion coefficient of Pb complexes decreased with increasing size of the ligand, in the order of diglycolic acid (DGA), nitrilotriacetic acid (NTA), fulvic acid and humic acid. In freshwaters the contribution of fulvic acid species to measured DGT mass should be considered. No significant difference was found between the rate of diffusion of Cu and Cd through the mostly commonly used gel and the filter membrane at the face of the DGT device. Diffusion coefficients obtained using a gel with small pore size (restricted gel) plus filter membrane were higher than those obtained using the restricted gel alone. It may be necessary to modify the standard DGT equation for restricted gel deployments, to take into account the difference in diffusion between the gel and the filter membrane.
