Diffusivity of Solutes Measured in Glass Capillaries Using Taylor's Analysis of Dispersion and a Commercial CE Instrument

Abstract

We present a strategy for the rapid, efficient, and accurate measurement of the coefficient of diffusion (D) of solutes using a commercial capillary electrophoresis (CE) instrument. This approach utilizes the classic analysis of Taylor of the dispersion of solutes pumped hydrostatically through glass capillaries. To obtain accurate values of D, we modified Taylor's analysis of dispersion to account for the finite time required to reach steady-state flow in the capillary when using a CE instrument. Neglecting this effect results in measured diffusivities of phenylalanine, a model solute, that are in error by as much as 60% when compared with published values. We provide an analysis of this effect and a simple strategy for avoiding these errors. Using this approach, we analyze profiles of concentration fronts and measured values of D for phenylalanine to within 5% of published values. We also analyze profiles of pulses of solute. To determine values of D accurately, measurements of dispersion first need to be made as a function of injection volume to correct for the finite width of the injection plug, before they are corrected for unsteady-state flow. This approach also yields values of D for phenylalanine to within 5% of published values. In contrast to other techniques used for the determination of D, this approach requires no fluorescent labeling and is applicable to solutes of any molecular weight.