Tracer composition gradient

Eluent delivery was provided by two model 510 high-pressure pumps coupled with automated gradient controller model 680 (Waters Chromatography Division, Millipore, MA, USA) and a model 7125 infection valve with a 20-(il loop from Rheodyne (Cotati, CA, USA) Stainless-steel columns (30 x 0.40 cm I.D.) packed from Tracer Analltica (Barcelona, Spain) with 10 un particle diameter Spherisorb ODS-2 (Merck, Darmstadt, FRG) were used. Four different LC mobile phase compositions were tested acetonitrile-water... 

Membrane Diffusion in Dilute Solution Environments. The measurement of ionic diffusion coefficients provides useful information about the nature of transport processes in polymer membranes. Using a radioactive tracer, diffusion of an ionic species can be measured while the membrane is in equilibrium with the external solution. This enables the determination of a selfdiffusion coefficient for a polymer phase of uniform composition with no gradients in ion or water sorption. In addition, selfdiffusion coefficients are more straightforward in their interpretation compared to those of electrolyte flux experiments, where cation and anion transport rates are coupled. 

The term "tracer diffusion" is often used to refer to measurements in which two forms of the species of interest diffuse into each other. The difference between the two forms is typically in isotopic composition or optical rotation it should have a negligible effect on the chemical properties but allow for detection of a concentration gradient between the two forms. If the two forms of the solute are sufficiently similar, then the measured value is the same as the intradiffusivity. In actuality, though, this is a nonequilibrium ternary system [40]. 

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