Immersion probe Raman for pharmaceutical suspension testing in the manufacturing plant and laboratory: Flow considerations for quantitative applications.

Traditional analysis of pharmaceutical suspensions by liquid chromatography requires time, manual sample preparation, and solvents. In this work, we explored an alternative procedure for quantifying the active pharmaceutical ingredient (API) of liquid samples using a non-destructive method, back scattering Raman with an immersion probe, with no additional sample preparation in lab-based off-line and plant-based in-line settings. Coupling the Raman signal to compact high-performance liquid chromatography (HPLC) measurements was a useful way to monitor the suspension transfer and filling process during investigational studies. That process entailed a flowing, rather than static, suspension. Therefore, understanding the impact of a flowing suspension on the Raman signal of the API for quantitation was critical. To help address the lab-based and production-scale applications, we developed a theoretical framework for measuring flowing suspensions by Raman, created chemometric models for lab use, and experimentally investigated the impact of flowing versus static suspensions on back scatter Raman measurements.