Novel Application of an <i>In Situ</i> Raman Technique for a Co-Crystal Ternary Phase Diagram Determination

Chemometric models were established using the Raman spectroscopy technique for in situ composition analysis of multi-component/multi-phase inorganic mixtures. The X-ray powder diffraction technique was then used to validate chemometric models. Subsequently, a novel method was developed to determine a co-crystal ternary phase diagram of an inorganic sodium salt system. The common method to determine a ternary phase diagram requires analyzing the composition of liquid and solid phases of each constituent separately. It is a time-consuming process, often with a certain level of inaccuracy depending on which analytical techniques are applied, i.e., chemical analysis during the solid–liquid separation will have weight loss especially for high-temperature processes. However, the in situ Raman technique is able to capture the dynamic changes during the operation, especially for fast processes, which helps to understand and quantify the real-time evolution of the chemicals/crystalline in the system without being influenced by sample preparation and methodology operation conditions. In addition, it is a faster method to characterize equilibrium systems as it quantifies when equilibrium is achieved. In this study, an isothermal ternary phase diagram was rapidly achieved by applying the in situ Raman technique together with the chemometric models. With this new approach, the composition information of each constituent was evaluated from this phase diagram over the operation time