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

• Ternary mutual diffusion coefficients of aqueous l-dopa plus hydrochloric acid at 25 °C.
• Diffusion of l-dopa driven by HCl gradients.
• Coupled diffusion of l-dopa and HCl.

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) 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. D21, for example, reaches values that are larger than D11, 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.

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