Diffusive gradients in thin film technique

Van Moorleghem C, Six L, Degryse F, Smolders E, Merckx R. Effect of organic P forms and P present in inorganic colloids on the determination of dissolved P in environmental samples by the diffusive gradient in thin films technique, ion chromatography, and colorimetry. Anal. Chem. 2011 83 5317-5323. 

Li, W., H. Zhao, P.R. Teasdale, R. John, and F. Wang. 2005. Metal speciation measurement by diffusive gradients in thin films technique with different binding phases. Anal. Chim. Acta 533 193-202. 

Leermakers, M., Y. Gao, C. Gabeille, et al. 2005a. Determination of high resolution pore water profiles of trace metals in sediments of the Rupel River (Belgium) using DET (diffusive equilibrium in thin films) and DGT (diffusive gradients in thin films) techniques. Water Air Soil Pollut. 166 265-286. 

In recent years, novel techniques called diffusive gradient in thin films technique (DGT) were developed for obtaining speciation data and preconcentration of uranium from aqueous samples (Li et al. 2006). The method employs a bottom layer of a binding phase and an upper layer of a permeable hydrogel covered with a filter membrane. The metal ions diffuse through the membrane and upper layer and are captured by the bottom layer that contains a resin embedded in a gel (usually acrylamide), as shown schematically in Figure 3.14 (Gregusova and Docekal 2011). 

Li, W., Zhao, J., Li, C. et al. (2006). Speciation measurements of uranium in alkaline waters using diffusive gradients in thin films technique, Anal. Chim. Acta 575, 274—280. 

DGT Diffusive gradient in thin-films technique (preconcentration... 

Diffusion Gradient in Thin films (DGT) and equilibrium techniques such as Peepers and DETs... 

The use of some other techniques, including electrodialysis, diffusion through membrane, diffusive gradient in thin-film (DGT) (Hooda et al. 2001), and bioindication has also been proposed. However,... 

From these examples, it is clear that diffusion can be a problem under some circumstances. From the palaeolimnologist s perspective, it is important to be able to predict where such problems will occur, and what their potential significance is. A promising approach to this is via modeling. Some hope is also offered by the diffusive gradients in thin-films (DGT) technique (e.g.. Harper et al., 1998), because it may then be possible to estimate at each site the relative mobility of the elements nnder study. 

Diffusive gradient in thin films A technique for measuring trace element availability (a combination of dissolved concentration and diffusive mobility) in sediment using sheets coated with exchange resin. 

H. Zang and W. Davidson. Performance characteristics of the technique of diffusion gradients in thin films (DGT) for the measurement of trace metals in aqueous solution. Anal. Chem., 67 3391-3400,1995. 

R.J.K. Dunn, P.R. Teasdale, J. Wamken, and P.R. Schleich. Evaluation of the diffusive gradient in a thin film technique for monitoring trace metal concentrations in estuarine waters. Environ. Sci. Technol, 37 2794-2800, 2003. 

The flash pyrolysis of starch has not yet been reported. In this technique, a thin film of polymer is heated rapidly (in one second, or less) to about 600", and the resultant, volatile compounds are immediately swept onto the gas-chromatographic column for analysis. The effects of thermal gradients in the sample, the diffusion of products, and secondary reactions are thus minimized. In the field of synthetic polymers, flash pyrolysis provides a convenient and rapid method of analysis, because the chromatogram produced is characteristic of the material. Chromatograms from the flash pyrolysis of cellulose have been described. ... 

Figure 6.23 illustrates a variety of situations . We will meet further cases, in Chapter 7, in which the fluxes and hence the gradients are kept constant at the boundary. Naturally the one-dimensional solutions are not restricted to one-dimensional systems (cf. Fig. 6.22). In a suitable pseudo one-dimensional experiment is the application of a diffusion source in the form of a thin strip (e.g. gold) onto a thin film (e.g. a thin sheet of silver) (chemical diffusion). It can also be a thin strip of the same but now radioactive material (different isotope), or the exposure of a slit-shaped opening of the otherwise sealed thin oxide film to a (radioactive or chemically modified) gas atmosphere (tracer diffusion). The analogue in D is the sandwich technique or the planar application of the diffusion source onto the surface (as already considered in Fig. 6.24). If the diffusion source is a gas phase, again sealing is necessary unless the aspect ratio is very favourable, i.e. if the extension is sufficiently small in the direction of diffusion compared with the other directions in space . Otherwise the three-dimensional solution has to be considered.

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