Raman Chemical Mapping of Magnesium Stearate Delivered by a Punch-Face Lubrication System on the Surface of Placebo and Active Tablets

Raman chemical mapping was used to determine the distribution of magnesium stearate, a lubricant, on the surface of tablets. The lubrication was carried out via a punch-face lubrication system with different spraying rates applied on placebo and active-containing tablets. Principal component analysis was used for decomposing the matrix of Raman mapping spectra. Some of the loadings associated with minuscule variation in the data significantly overlap with the Raman spectrum of magnesium stearate in placebo tablets and allow for imaging the domains of magnesium stearate via corresponding scores. Despite the negligible variation accounted for by respective principal components, the score images seem reliable as demonstrated through thresholding the one-dimensional representation and the spectra of the hot pixels that show a weak but perceivable magnesium stearate band at 1295 cm⁻¹. The same approach was applied on the active formulation, but no magnesium stearate was identified, presumably due to overwhelming concentration and spectral contribution of the active pharmaceutical ingredient.