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In electrical field flow fractionation (EFFF or EIFFF), an electric potential is applied across a narrow gap filled with a weak electrolyte fluid. Charge buildup at the two poles (electrodes) and the formation of an electric double layer shields the channel, making the effective field in the bulk fluid very weak. Recent computational research suggests that pulsed field protocols, however, should improve retention and may enhance separation in EFFF through systematic disruptions of the double layer resulting in a stronger effective field in the bulk fluid. Improved retention has already been demonstrated experimentally. Accurate modeling and subsequent device optimization and design, however, depends, in part, on formulating a suitable model for the capacitative response of the channel and double layer at the electrode surfaces. Early models do not correctly describe experimentally observed current-time response and are not physically meaningful even when accurate mathematical fits of the data are realized. A new model and conceptual framework based on electrical resistance and capacitance variations of the double layer is suggested here. Physical interpretations of the electrical response have been developed and compared to published experimental data sets.

An instrument is developed to measure rates of desorption of solutes from particulate HPLC packing materials for processes that are quantitatively complete in a few tenths of a second. The instrument is a modified, pressure-driven, stopped-flow device. The major modifications include positioning a very short (0.6 mm) bed of the particles just upstream of the detector cell, eliminating the mixing chamber, and adding high-speed switching valves in order to allow sequential continuous flow of individual solutions. Instantaneous rate curves are measured for the desorption of 1,2-dimethyl-4-nitrobenzene (DMNB) from 12-[micro]m-diameter porous particles of the bonded-phase packing Luna C-18 employing high linear velocities of the eluting solvent. The same experiment is performed for the nonsorbed compound phloroglucinol (PG) The PG rate curve is used in two ways (i.e., subtraction and deconvolution) in order to correct the observed rate curve of DMNB for experimental artifacts such as bed hold-up volume and instrument band broadening. The cumulative desorption rate curve of DMNB is obtained by integration. It is accurately described ([R.sup.2] > 0.999) by a theoretical model that invokes both intraparticle diffusion (including both hindered pore diffusion and surface diffusion) and external film diffusion. The surface diffusion coefficient is (3.2 [+ or -] 0.8) x [10.sup.-6] [cm.sup.2]/s and the diffusion film thickness is 0.5 [micro]m. The validity, of both the experimental technique and the theoretical model, is demonstrated by excellent agreement between a predicted and an observed chromatographic elution peak for DMNB on a 25-cm-long commercial column of Luna C-18.

The nature of the interfacial structure of electrolyte solution is explored and a detailed description is given on the emerging revised picture. The emerging picture of the surface structure of electrolytic solution refines, rather than contradicts, the existing textbook descriptions, which is consistent with both theory and experiments.

A novel integral equation method is described for calculating fluid structure in the vicinity of a plane impenetrable wall, which is based on the reference site interaction model (RISM) equation. Wall-fluid site density distributions, charge density, field and potential profiles are calculated for pure water and aqueous electrolyte solutions with varying concentrations adjacent to an uncharged soft wall.

The mean activity coefficient of electrolyte solutions, [gamma], specifically, the case [gamma] is less than or equal to 1, is analyzed. A model of electrolyte solution based on a psuedolattice approach is presented to compute [gamma] without using fitting parameters, where the (upper)concentration is present at which the electrolyte solution shows [gamma] is equal to 1 (molality scale).

The temperature-dependence of excited-state proton transfer in water electrolyte solutions and water-methanol solutions was studied using 8-Hydroxypyrene-1,3,6-trisulfonate trisodium salt as photoacid. The value of proton-transfer rate constant in pure water solution was almost independent of temperature at high temperatures, while its dependence increased with decrease in temperature, at low temperatures.

The controversial observation of a minimum in the surface tension of dilute aqueous electrolyte solutions by Jones and Rays in the 1930s is confirmed by resonance-enabled second harmonic generation experiments. The experiments show that the quadruply charged ferrocyanide, Fe(CN)6(super 4-), anion is not surface active at high concentration, as expected, but at dilute concentrations, the anion is strongly attracted to the interface with a Gibbs free energy of adsorption of -6.8 kcal/mol.

Concentration up to about 1M describes the osmotic coefficients of a series of 16 aqueous electrolyte solutions. Although the description of bulk properties is satisfactory, prediction of surface tensions of the corresponding solutions (hotmeister series) is not very successful.