Coupled tracer diffusion coefficients of solubilizates in ionic micelle solutions from liquid chromatography

The peak-broadening (Taylor dispersion) method is used to measure the diffusion of traces of alcohols (ethanol, n-butanol, n-hexanol, n-octanol, n-decanol) in aqueous solutions of sodium dodecylsulfate micelles at 25°C. A small quantity of each alcohol is injected into a long capillary tube containing a laminar stream of the micelle solution. The tracer diffusion coefficient is calculated from the broadened distribution of the eluted alcohol which is measured by differential refractometry. The fraction of each alcohol that is solubilized by the micelles is estimated from the drop in the diffusion coefficient relative to the value for the free alcohol molecules in pure water. The refractive index profiles across the dispersed samples are analyzed to obtain the cross-diffusion coefficient which gives the coupled flow of sodium dodecylsulfate produced by the tracer diffusion of each alcohol.