In Situ Monitoring of Antisolvent Cocrystallization by Combining Near-Infrared and Raman Spectroscopies

In situ monitoring techniques are essential for the control and optimization of the cocrystallization process. In our previous study, we successfully monitored indomethacin–saccharin (IMC–SAC) cocrystallization by antisolvent addition using a method based on near-infrared principal component analysis (NIR–PCA). In this study, a calibration model was developed to predict the solute concentration of the two components. Several samples withdrawn from five sets of experiments were used to develop the calibration model. The actual concentrations of the two components were determined using UV–vis spectroscopy and high performance liquid chromatography (HPLC). The amount of solid-phase material in suspension was calculated from these solute concentration data. Correlations between NIR spectra and solid concentrations were evaluated using partial least-squares (PLS) regression analyses. Reasonably good calibration models with determination coefficients (R²) higher than 0.979 were obtained. Process monitoring was performed using in situ NIR and Raman spectroscopies to predict the concentrations of both IMC and SAC in solution and to identify the solid-phase materials, respectively. The calibration models were deemed suitable, with reasonable accuracy and precision, for in situ concentration monitoring of the antisolvent crystallization of IMC–SAC cocrystals. This combination of NIR and Raman spectroscopies was able to detect the formation and phase transition of the resulting cocrystal.