Rapid determination of hydrodynamic radii beyond the limits of Taylor dispersion.

Taylor dispersion analysis (TDA) is an absolute method for determining the diffusion coefficients, and hence the hydrodynamic radii, of particles by measuring the dispersion in a carrier medium flowing within a capillary. It is applicable under conditions which allow the particles to radially diffuse appreciably across the cross-section of the flow before the measurement and therefore implies long measurement times are required for large particles with small diffusion coefficients. In this paper, a method has been developed by which the diffusion coefficients of large particles can be rapidly estimated from the shapes of the concentration profiles obtained at much earlier measurement times. The method relies on the fact that the shapes of the early-time concentration profiles are dependent on the diffusion coefficient, flow rate and the capillary radius through the dimensionless residence time which, theoretically, is a measure of the amount of radial diffusion undergone by the particles. The amount of radial diffusion for nanospheres of varying sizes was estimated by quantifying the relative change in the shapes of concentration profiles obtained at two points in the flow and a correlation was obtained with the variation of the dimensionless residence time to confirm the theory. This correlation was then tested by applying it to another set of measurements of solutes and solute mixtures of different sizes including a protein. The estimated diffusion coefficients were found to be in good agreement with the expected values. This demonstrates the potential for the method to extend dispersion analysis to regimes well outside the TDA limits to enable the rapid characterization of large particles.

Analytical mitigation of solute-capillary interactions in double detection Taylor Dispersion Analysis.

Taylor Dispersion Analysis (TDA) in the presence of interactions between solutes and capillary walls yields inaccurate results for the diffusion coefficients of the solutes because the resulting concentration profiles are broadened and asymmetric. Whilst there are practical ways of mitigating these interactions, it is not always possible to eradicate them completely. In this paper, an analytical method of mitigating the effects of the adsorptions is presented. By observing the dispersion of the solute molecules at two detection points and using the expected relations between measured parameters, such as the standard deviations and peak amplitudes, the dispersive components of the profiles were isolated with a constrained fitting algorithm. The method was successfully applied to lysozyme and cytochrome C which adsorb onto fused silica capillary walls. Furthermore, this illustrates an advantage of using the fitting method for Taylor Dispersion Analysis.

Application of the Exact Dispersion Solution to the Analysis of Solutes beyond the Limits of Taylor Dispersion.

Taylor dispersion analysis (TDA) is a fast and simple method for determining hydrodynamic radii. The method is applicable under conditions that allow the solute molecules to diffuse appreciably across the cross section of the flow before its measurement. This mitigates the effects of early stage convection on the dispersion and thus imposes a lower bound on the value of the diffusion coefficient measurable at a given flow speed. In this paper, we use the exact solution to the dispersion problem to analyze solutes outside the limits of TDA. Furthermore, by modeling the early stage convection, we analyze a mixture of two solutes with significantly different sizes that mimics heavily aggregated samples. The results obtained from the fits in both cases were in good agreement to the expected values. This demonstrates the potential of the model to extend dispersion analysis to regimes well outside the TDA limits such as the analysis of large molecules and the use of high flow-rates.