CHARACTERIZATION OF THE SOLID-LIQUID INTERFACE ON CHEMICALLY MODIFIED PARTICULATE SURFACES (CHROMATOGRAPHY, ISOTHERM).

Abstract

A method for representing solid-liquid sorption behavior of solutes by a two step equilibrium is shown to correlate well with observed sorption behavior. By fitting a three term expression to isotherm plots of solute surface concentration vs. the concentration in the bulk solvent the two distribution constants as well as the maximum sorption capacity are determined. Isotherms for hydrocarbon-modified silica are determined for various solvents and solutes. Interpretation of sorption behavior is presented in terms of values determined for sorption capacity and the distribution coefficients. The isotherm model parameters are shown to correlate to the chromatographic retention parameter, k'. Sorption capacity is proposed as a more meaningful representation of the chromatographic phase ratio. Reversed-phase chromatographic retention and efficiency are shown to be affected by ion modifiers as well as the temperature history of a system when a totally aqueous mobile phase is used. The dynamic nature of the octylsilane modified surface is discussed in terms of changes which are induced by cations exchanged on the silica surface and imbibed organic solvent in the bonded hydrocarbon chain previously used to condition the surface. Both polar and non-polar solutes are used and their retention behavior allows interpretation of changes in specific regions of the surface. The development of magnetic Field-Flow Fractionation (Magnetic FFF), a separation technique for small magnetic particles, is described as well as the parameters which affect such separations. The use of a FFF device to characterize small particle suspensions is demonstrated. The change in turbidimetric response of iron oxide particle suspensions in a spectrophotometric device under the influence of a magnetic field is interpreted in terms of the difference in particle shape.