A Step Towards Real-Time Release Testing of Pharmaceutical Tablets: Utilization of CIELAB Color Space

Background: The pharmaceutical industry is shifting from end-product testing towards real-time release testing. This approach is based on the continuous collection of process data and product information, which is finally utilized for the release decision. For continuous direct compression, spectroscopic technologies are preferred due to their short acquisition time and non-destructive nature. Methods: Here, the feasibility of the CIELAB color space was demonstrated for porosity and tensile strength. Five different formulations were processed, varying in particle size and deformation behavior. The compression forces were varied from 3 to 18 kN and the CIELAB color space was measured in-line using a UV/Vis probe implemented in the ejection position of the tablet machine. Results: Increasing the main compression force during tableting decreases the tablet surface roughness and porosity. In addition, the tablet tensile strength increases. These changes affected the reflection behavior of radiation on the tablet surface, resulting in a change in the chroma value C*. These dependencies were utilized for the in-line monitoring of porosity and tensile strength. Linear relations were observed for all formulations as exemplary, indicated by sufficient coefficients of determination and verification runs. Conclusions: Finally, UV/Vis diffuse reflectance spectroscopy in combination with a CIELAB color space transformation was demonstrated to be a suitable real-time release tool.