Glycine Dissolution Behavior under Forced Convection

The integration of a flow-through cell into a Mach–Zehnder interferometer offers the possibility to study the dissolution of crystals in detail. The influence of flow on the displacement velocity of a specific crystal facet and the distribution of the solute concentration around the crystal are measured simultaneously in a time-resolved manner. The disintegration from the crystal surface and the mass transfer into the solvent can be separated. We aim to establish an in vitro experiment that improves the quality of prediction for the bioavailability of active pharmaceutical ingredients. In the presented feasibility study, glycine was used as a model substance. It was successfully demonstrated that the set-up is suitable for observing disintegration and mass transfer separately. The description of the dissolution rate in terms of the Sherwood number as a function of Reynolds, Schmidt and Grashof numbers clearly shows that with increasing flow rate there is a transition from natural to forced convection as the dominant mass transfer mechanism. Temporal and spatial resolved concentration fields visualize the convective mass transfer and also show the influence of convection on the diffusive boundary layer. No limitation of the dissolution by surface disintegration could be found in the examined range of flow rates.