Moments analysis of strongly coupled diffusion in taylor dispersion profiles. Sodium hydroxide–sodium dodecyl sulfate–water

Abstract

A procedure for calculating ternary diffusion coefficients from the heights, areas and first moments of Taylor dispersion peaks is developed to interpret the unusual dispersion behaviour of aqueous solutions of NaOH–sodium dodecyl sulfate (NaDS). When a sample of NaOH is injected into an aqueous NaDS carrier stream, the refractive index profile across the eluted sample is bisected by a deep valley which descends farther below the baseline than the peak extends above the baseline. The analysis shows that the unusual peak shape is caused by a large coupled flow of NaDS which is driven by the diffusing NaOH. Evidence is presented which suggests that the interaction between the diffusing NaDS and NaOH is primarily electrostatic. The procedure for calculating diffusion coefficients is tested on aqueous solutions of sucrose–KCl, LiCl–KCl, tetrabutylammonium bromide–KBr and NaCl–MgCl₂.