Application of Raman microscopy and band-target entropy minimization to identify minor components in model pharmaceutical tablets

The aim of the current study is to establish a useful analytical technique to detect and identify minor components of pharmaceutical drug tablets using Raman microscopy and advanced multivariate data analysis method, namely band-target entropy minimization (BTEM). Model pharmaceutical tablets comprising four components with varying proportions were prepared with a custom press tooling after blending. One of the components, magnesium stearate, was made as a minor component, with weight percentages of 2%, 1%, 0.5%, and 0.2% in four model tablets. Raman point-by-point mapping was performed on an area of 200 μm × 200 μm using a near infrared laser source and a 50× objective lens with a step size of 5 μm in both the x and y directions. Advanced multivariate analysis, BTEM, was then performed on the Raman mapping data to recover all observable pure component spectra. BTEM was successfully applied to recover the pure component spectrum of magnesium stearate, which was present as a minor component (as low as 0.2 wt%) in the prepared tablet. The success of BTEM in identifying minor chemical species offers a new analytical technology for detecting impurities or any other minor components in pharmaceutical tablets.