Numerical evaluation of lateral diffusion inside diffusive gradients in thin films samplers.

Jakob Santner,Walter W Wenzel,Andrea Schnepf,Andreas Kreuzeder

doi:10.1021/acs.est.5b00134

Jakob Santner, Walter W Wenzel + Show 2 more

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https://doi.org/10.1021/acs.est.5b00134

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Using numerical simulation of diffusion inside diffusive gradients in thin films (DGT) samplers, we show that the effect of lateral diffusion inside the sampler on the solute flux into the sampler is a nonlinear function of the diffusion layer thickness and the physical sampling window size. In contrast, earlier work concluded that this effect was constant irrespective of parameters of the sampler geometry. The flux increase caused by lateral diffusion inside the sampler was determined to be ∼8.8% for standard samplers, which is considerably lower than the previous estimate of ∼20%. Lateral diffusion is also propagated to the diffusive boundary layer (DBL), where it leads to a slightly stronger decrease in the mass uptake than suggested by the common 1D diffusion model that is applied for evaluating DGT results. We introduce a simple correction procedure for lateral diffusion and demonstrate how the effect of lateral diffusion on diffusion in the DBL can be accounted for. These corrections often result in better estimates of the DBL thickness (δ) and the DGT-measured concentration than earlier approaches and will contribute to more accurate concentration measurements in solute monitoring in waters.

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A diffusive gradients in thin films (DGT) sampling unit consists of a resin gel, covered by a diffusive gel with a defined thickness and a protective membrane, all of which are enclosed in a sampler housing.[1,2]The sampling process is simple: once the DGT device gets in contact with the sampled medium, the target solutes diffuse into the sampler where they get bound by the resin gel
Using numerical simulation of diffusion inside diffusive gradients in thin films (DGT) samplers, we show that the effect of lateral diffusion inside the sampler on the solute flux into the sampler is a nonlinear function of the diffusion layer thickness and the physical sampling window size
Lateral diffusion is propagated to the diffusive boundary layer (DBL), where it leads to a slightly stronger decrease in the mass uptake than suggested by the common 1D diffusion model that is applied for evaluating DGT results

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A DGT sampling unit consists of a resin gel, covered by a diffusive gel with a defined thickness and a protective membrane, all of which are enclosed in a sampler housing.[1,2]The sampling process is simple: once the DGT device gets in contact with the sampled medium, the target solutes diffuse into the sampler where they get bound by the resin gel. We investigate the effect of applying the nonconstant correction coefficients determined in this study on the results of DBL thickness estimations using (1) a simulated data set and (2) literature data.

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