Optical method for dissolution/diffusion process multiparameters simultaneous measurement based on liquid-core cylindrical lenses

The dissolution/diffusion process of solid in a liquid is a kind of widespread physical phenomenon. Parameters involved in this process include the dissolution rate (<i>dC/dt</i>), dissolution rate constant (<i>K</i>), and diffusion coefficient (<i>D</i>), whose accurate measurement is particularly important in fields such as biopharmaceuticals, materials science, agriculture, etc. However, the commonly used measurement methods at present cannot obtain these parameters simultaneously. Besides that, the measurement process is always not intuitive and time-consuming. This study introduces a method for measuring the multiple parameters of potassium dihydrogen phosphate (KDP) dissolving and diffusing in water under three states (powder, solid, and crystal) based on a compound liquid-core cylindrical lens (SLCL-Doublet) using a real-time optical image feature extraction method. Based on the relationship between the dissolution/diffusion image width and the solution concentration, dynamic spatiotemporal distribution of the solution concentration can be established, which can be used to calculate the <i>D</i> values based on Fick's second law, and the <i>dC/dt</i>, <i>K</i> values based on Noyes-Whitney equation, accordingly. At last, the area of solid-liquid contact surfaces is determined based on the relationship between <i>K</i> and <i>D</i> in the Nernst-Brunner equation, confirming the accuracy of the measurement data from the side. The optical method for simultaneously measuring the multiple parameters in the dissolution/diffusion process introduced in this study can be widely used to quickly expand the basic data required for chemical and pharmaceutical industries.