Salt effects on the diffusion of caffeine in aqueous solutions

Taylor dispersion has been used to measure ternary mutual diffusion coefficients (D11, D12, D21, and D22) for aqueous solutions of caffeine (1) with added salt (2) (LiCl, NaCl, KCl, RbCl, CsCl, or NiCl2). The measurements were made at 25 °C and salt concentrations up to 1.00 mol dm−3. Salt effects on the transport of caffeine are assessed by comparing the diffusion coefficient of caffeine in salt-free solutions with the caffeine main diffusion coefficient (D11) measured for the caffeine + salt solutions. Coupled diffusion of caffeine and salt, as indicated by cross-diffusion coefficients D12 and D21, is discussed in terms of salting-out effects and the possible formation of caffeine–metal ion complexes.