Coupled mutual diffusion in aqueous sodium (salicylate + sodium chloride) solutions at 25 °C

Abstract

Taylor dispersion is used to measure the binary mutual diffusion coefficient (D) of aqueous solutions of sodium salicylate (NaSal), a non-steroidal anti-inflammatory drug (NSAID). The D° value estimated by extrapolation to zero NaSal concentration is used to calculate the limiting mobility of the Sal− ion for comparison with the value determined previously from conductivity data. Salt effects on NSAID diffusion are studied by measuring the ternary mutual diffusion coefficients (Dik) of aqueous NaSal(C1) + NaCl(C2) solutions, including results for the diffusion of NaSal in physiological saline solutions with C2 = 0.15 mol dm−3. As the NaCl:NaSal ratio increases, NaSal diffusion coefficient D11 changes from the binary diffusion coefficient of aqueous NaSal (a weighted average of the Na+ and Sal− diffusion coefficients) to the tracer diffusion coefficient of the Sal− ion in NaCl solutions. Coupled diffusion in the solutions is analysed by using Nernst-Planck equations to calculate the fluxes of ions migrating in the electric field (diffusion potential) generated by NaSal and NaCl concentration gradients.