Evaluation of solid dispersions on a molecular level by the Raman mapping technique

Troglitazone containing two asymmetric carbons has four isomers. Crystalline troglitazone consists of two crystalline diastereomer-pairs, RR/SS and RS/SR, which have different melting points. Using a closed melting method, troglitazone–polyvinylpyrrolidone solid dispersions with various crystallinities were prepared. Raman spectroscopy and its mapping technique were applied to discriminate between the crystalline RR/SS, crystalline RS/SR and amorphous form of troglitazone in solid dispersions. The results of the Raman mapping of solid dispersions showed the co-existence of crystal and amorphous forms, and which diastereomer-pairs remained as crystals, in addition to the distribution of the drug. Moreover, the distribution of PVP could be illustrated from the Raman mapping data. Thus, Raman spectroscopy and its mapping technique are useful tools to evaluate crystal and amorphous states, including discrimination of crystalline diastereomer-pairs in solid dispersions. In addition, by describing the distribution of the drug and the carrier, it could be guessed how drug crystals become amorphous during preparation from the point of view of the distribution of the amorphous form of the drug substance and the carrier.