An investigation into the subambient behavior of aqueous mannitol solutions using differential scanning calorimetry, cold stage microscopy, and X-ray diffractometry
✍ Scribed by Vicky L. Kett; Shaun Fitzpatrick; Brett Cooper; Duncan Q.M. Craig
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 410 KB
- Volume
- 92
- Category
- Article
- ISSN
- 0022-3549
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✦ Synopsis
The subambient behavior of aqueous mannitol solutions is of considerable relevance to the preparation of freeze dried formulations. In this investigation the properties of 3% w/v mannitol solutions were investigated using differential scanning calorimetry (DSC), cold stage microscopy (CSM), and X-ray diffraction (XRD) to identify the thermal transitions and structural transformations undergone by this system. It was found that on cooling from ambient the system formed ice at circa À208C while a further exotherm was seen at approximately À308C. Upon reheating an endotherm was seen at circa À308C followed immediately by an exotherm at circa À258C. Temperature cycling indicated that the thermal transitions observed upon reheating were not reversible. Modulated temperature DSC (MTDSC) indicated that the transitions observed upon reheating corresponded to a glass transition immediately followed by recrystallization, XRD data showed that recrystallization was into the b form. Annealing at À358C for 40 min prior to cooling and reheating resulted in a maximum enthalpy being observed for the reheating exotherm. It is concluded that on cooling 3% w/v aqueous mannitol solutions an amorphous phase is formed that subsequently recrystallises into the b form. The study has also shown that DSC, CSM, and XRD are useful complementary techniques for the study of frozen systems.