Assessment of the solid-state composition of an active salicylanilide compound by FT-Raman spectroscopy

A biologically active salicylanilide compound currently appears in three known solid-state forms: polymorph I (Pol I), polymorph II (Pol II) and the amorphous form (Amorph). The obtained FT-Raman spectra revealed several regions of interest (ROIs) qualitatively distinguishing the different forms, allowing samples with an unknown polymorphic composition to be quantitatively analysed by FT-Raman spectroscopy. The Markov-transformed peak areas of the Raman-bands in the ROIs from the samples were determined and compared with the transformed peak areas obtained for the reference solid-state forms. A constrainted linear regression model estimated the contribution of each reference to the different samples. The applicability of this approach was demonstrated by analysing commercially available batches.