A hydrodynamic method for the measurement of Laponite-RD caffeine binding

• Binding isotherm between dispersed, Laponite platelets and small molecules determined
• Determination based on hydrodynamic chromatography principles
• Symmetry of eluting peaks varies from diffusivity differences between analytes

A novel flow-based technique to determine effective binding constants between caffeine and dispersed Laponite-RD particles in aqueous dispersions is presented. The technique, which is based on wide-bore hydrodynamic chromatography principles, exploits diffusion coefficient and flow profile differences between caffeine and Laponite-RD. A high-pressure liquid chromatography pump is used to create a laminar flow of mobile phase through a 0.25 mm diameter capillary; flow conditions are optimized in the capillary to exploit differences in diffusion coefficients of the dispersed Laponite-RD particles and caffeine. Different flow profiles for Laponite-RD and caffeine result enabling a deconvolution algorithm to determine the concentrations of caffeine associated with the Laponite-RD, a model nanoparticle, as well as the caffeine free in solution. Using these data, binding isotherms are presented from which an effective binding constant of caffeine associated with Laponite-RD can be obtained.