Raman spectroscopic imaging of indomethacin loaded in porous silica

Abstract

Loading of a poorly soluble drug such as indomethacin (IMC) into porous silica particles enhances its dissolution upon administration. The distribution of the different solid forms in which IMC may appear was studied using Raman spectroscopy. Raman mapping of the samples was performed with a Raman microscope equipped with an automated xy-stage. The spectral data were extracted in the range 1500–1750 cm⁻¹, which represents the stretching of the CO bond in the IMC molecule. To alleviate the problem of overlapping peaks in the Raman spectra of the different IMC forms, the spectral data were analyzed using partial least squares (PLS) and principal component analysis (PCA). Despite the problems caused by fluorescence, the method gave valuable information about the occurrence and distribution of the solid forms of IMC. The same approach was utilized for analysis of the heterogeneity of recrystallized IMC samples, and PCA was shown to be capable of revealing the presence of solvates or polymorphs not included in the model.