The influence of different acquisition settings and the focus adjustment on Raman spectral maps of pharmaceutical tablets
Pharmaceutical tablets contain a variety of active substances and excipients which could be monitored by Raman spectroscopy/microscopy. Raman microscopic spectra are affected not only by the sample composition but also by preparation/measurement conditions. The character and variability of surface morphology (of tablet slices), the appropriate levels of focusing and other adjustable settings ofthe measurement instrumentation represent important parameters to be considered for obtaining relevant and reliable results by Raman microscopic mapping/imaging analysis in the pharmaceuticalpractice. The aim of the study is to determine the effect of levels of the spotlight, and other instrumental parameters for mapping industrially manufactured pharmaceutical tablets and to find outsuitable, preferably robust, parameters for routine analyses. The role of roughnesses produced by commonly used microtome slices of tablets was investigated experimentally by different focusinglevels showing relatively weak (statistical) influence on data sets. The spectral quality was evaluated by signal–to–noise ratio. The data sets were processed using two multivariate statisticalmethods (Principal Component Analysis, Soft Independent Modeling of Class Analogy). Direct Classical Least Squares statistical modeling was optimized to show the distribution of active pharmaceuticalingredient and excipients in Raman maps. The applied different types of data evaluation confirm that the most suitable position regarding the focusing is the middle of tablet’s cross-sectionroughness. However, we have shown that the selection of microscopic measurement modes plays a much more significant role. The selection of proper measurement mode is crucial to describe the actualsample variability and to obtain relevant data for real pharmaceutical samples. The time–consuming requirements of measurement modes need to be considered, as well, to obtain as reasonable data aspossible in the given time frame in the applied pharmaceutical analysis.