Entwicklung und Anwendung einer enantioselektiven Raman-Spektroskopie zur Untersuchung chiraler Medien

A variety of pharmaceuticals consists of chiral molecules, which are brought to the market in the enantiopure form in an increasing amount. Thus, rapid chiral discrimination is an industrially relevant topic for in-process monitoring. The diverse existing, well-established and commercially available methods for chiral analysis mainly exhibit disadvantages concerning, e.g. measurement time, sample preparation, or high maintenance. The present work aims to close the gap by developing a method for the rapid, real-time analysis of chiral media based on polarization-resolved Raman spectroscopy, the enantioselective Raman (esR) spectroscopy. The chiral resolution is based on the optical activity of the chiral sample in combination with a phase-shifter in the signal collecting unit, breaking the Raman intensity symmetry exhibited by the enantiomers. This work demonstrates the first experimental application of esR spectroscopy in 90° scattering geometry for chiral discrimination. The experimental setup is developed and characterized. Additionally, different approaches for data evaluation are proposed and applied. The data evaluation contains not only classical, e.g. the intensity comparison of selected vibrational bands, but chemometrical approaches such as principal component analysis (PCA) or partial least-squares regression (PLSR), and the 2D correlation spectroscopy (2D-COS) as well. The chiral discrimination is shown for the enantiopure chiral media with classical approaches, PCA, and 2D-COS. In a next step, the enantiomeric ratio is determined by PLSR over the full range of enantiomeric fraction. In addition, simulations are conducted for the esR spectroscopy with an existing 3D ray-tracing based model.