Diffusion of levodopa in aqueous solutions of hydrochloric acid at 25 °C

Abstract Ternary mutual diffusion coefficients ( D 11 , D 22 , D 12 and D 21 ) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa ( l -dopa) + HCl} solutions at 25 °C and HCl concentrations up to 0.100 mol · dm −3 . The coupled diffusion of l -dopa (1) and HCl (2) is significant, as indicated by large negative cross-diffusion coefficients. D 21 , for example, reaches values that are larger than D 11 , the main coefficient of l -dopa. Combined Fick and Nernst–Planck equations are used to analyze the proton coupled diffusion of l -dopa and HCl in terms of the binding of H + ions to l -dopa and ion migration in the electric field generated by l -dopa and HCl concentration gradients.