Evaluation of the Microcrystallinity of a Drug Substance, Indomethacin, in a Pharmaceutical Model Tablet by Chemometric FT-Raman Spectroscopy

PurposeTo establish a chemometric method for the precise evaluation of the microcrystallinity of indomethacin (IMC) in a pharmaceutical model tablet, based on FT-Raman spectroscopy.MethodsStandard sample powders of homogeneous mixtures of amorphous and crystalline IMC were prepared in various proportions. A calibration model for the crystallinity of IMC was constructed by partial least-square (PLS) analysis based on the multiplicative scatter correction (MSC) + second-derivative transformed Raman spectra. A calibration model for the crystallinity of IMC in a model pharmaceutical product (IMC/mannitol = 1:9 wt/wt) was also constructed using homogeneous standard sample powders of various degrees of crystallinity of IMC.ResultsThis technique was validated to detect to 2% an amorphous or crystalline material in IMC contained in the model product (0.2% of the total mass of the tablet). Using this technique, not only pressure-induced amorphization but also the difference in microcrystallinity of IMC at the surface and interior of a model product tablet was elucidated after compaction of the tablet.ConclusionsThe established technique is ideally suited for precise quantification of microanalysis of drug substances and drug products, particularly at the surface and interior of the tablet.