Interfacial reaction kinetics

To ensure that the detector electrode used in MEMED is a noninvasive probe of the concentration boundary layer that develops adjacent to the droplet, it is usually necessary to employ a small-sized UME (less than 2 /rm diameter). This is essential for amperometric detection protocols, although larger electrodes, up to 50/rm across, can be employed in potentiometric detection mode [73]. A key strength of the technique is that the electrode measures directly the concentration profile of a target species involved in the reaction at the interface, i.e., the spatial distribution of a product or reactant, on the receptor phase side. The shape of this concentration profile is sensitive to the mass transport characteristics for the growing drop, and to the interfacial reaction kinetics. A schematic of the apparatus for MEMED is shown in Fig. 14. 

Scherer, H.W. Zhang, Y. (1999) Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. 1. Effect of iron oxides on ammonium fixation. J. Plant Nutr. Soil Sci. 162 593-597 Scherer, M.M. Balko, B.B. Tratnyek, P.G. (1998) The role of oxides in reduction reactions at the metal-water interface In Sparks, D.L. Gmndl.T.J. (eds.) Mineral-Water Interfacial Reactions, Kinetics and Mechanisms ACS Smposium Series 715, Am. Chem. Soc., 301-322... 

The CPC present in the aqueous phase is distributed between the aqueous and organic phases at the SLM-liquid interface. By maintaining low Cl ion concentration in the feed phase and high Cl ion concentration in the stripping phase, the distribution ratio of CPC (P ion form) at the aqueous feed-SLM interface can be made much higher than that at the aqueous strip-SLM interface. Under this condition, the steady-sate overall CPC flux across the membrane can be obtained from Pick s distribution law applied to aqueous diffusion film as well as the membrane itself and from interfacial reaction kinetics which describe the interfacial flux. 

The time required to reach static equilibrium is higher than for homogeneous immunoassays. Like in the case of solid-phase immunoassays, this behavior can be related to the diffusion dependence of interfacial reaction kinetics, directly correlated with the ratio of the solution phase volume to the volume of the reactive interface. 

Scherer MM, Balko BA, Tratnyek PG. The role of oxides in reduction reactions at the metal-water interface. In Sparks DL, Grundl TJ, eds. Mineral-Water Interfacial Reactions Kinetics and Mechanisms. Washington, DC American Chemical Society, 1998 ACS Symp. Ser. 715 301-322. 

Sparks, D.L. et al., Kinetics and mechanisms of metal sorption at the mineral-water interface, in Mineral-Water Interfacial Reactions Kinetics and Mechanisms, in Sparks, D.L. and Grundl, T.J., Eds., American Chemical Society, Washington, D.C., 1998, p. 108. 

Comparing the simulated results with the experimental data, it appears that at higher flow rates, where boundary layers resistance becomes less important, membrane-strip interfacial reaction kinetics dominates as a ratecontrolling step for solute transport. 

Sparks DL, Grundl TJ (1998) Mineral-water interfacial reactions Kinetics and mechanisms. Am Chem Soc, Washington DC... 

Mineral-water interfacial reactions kinetics and mechanisms / Donald L. Sparks, editor, Timothy J. Grundl, editor. 

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