Comparison of dielectric constant meter with turbidity meter and focused beam reflectance measurement for metastable zone width determination

This work demonstrates a detailed process analytical technology (PAT) comparison study of dielectric constant measurement with turbidity measurement and focused beam reflectance measurement (FBRM) in detecting phase transitions during crystallization of three model solutions, namely stearic acid–ethyl acetate, paracetamol–ethanol and carbamazepine–methanol. The cloud and clear points determined by the dielectric constant measurement are found to be in close agreement with those obtained from the other two well-established PAT tools. A calibration technique can be further applied on the dielectric constant to improve the accuracy of the cloud point detection. The results have shown that the dielectric constant meter can be reliably used for metastable zone width (MZW) determination. This study opens new opportunities for the use of the dielectric constant meter as a simple and inexpensive alternative PAT tool for process monitoring of solution crystallization.

► Dielectric constant to determine cloud and clear points of solution crystallization.
► PAT comparison study of dielectric constant meter with turbidity meter and FBRM.
► Good agreement of the three PAT tools in determining the cloud and clear points.