Abstract
The transformation of monohydrate, dihydrate, two polymorphic forms (A and B) of anhydrate and the amorphous form of lactitol [(+)-4-O-β-D-galactopyranosyl-D-glucitol] were investigated by infrared spectrum, differential scanning calorimetry and X-ray powder diffraction. Monohydrate and dihydrate were transformed to anhydrate A and anhydrate B after storage at 80°C for 24 h under reduced pressure, respectively, but both hydrates changed to anhydrate A after being at 105°C for 3d. Five solid forms were stored under the relative humidity (RH) range from 12 to 93% at 25°C for 14 d. Monohydrate was transformed into dihydrate at RH more than 90%, but no change was observed in the range from 12 to 84% RH. Dihydrate did not show any transformation in the experimental RH range, though weight increase and decrease were observed at 12 and 93% RH, respectively. Both anhydrate A and B, however, were changed to monohydrate but this transformation occurred under different RH conditions (anhydrate A : 22% RH, anhydrate B : 75% RH). The amorphous form was transformed into monohydrate and dihydrate in the RH range from 53 to 84% and at 90% RH, respectively. The effect of grinding on the thermal behavior of the two hydrates was investigated, dehydration temperatures of monohydrate, which was determined by controlled rate thermogravimetry, was about 15°C lower than the intact monohydrate. However, no change in dehydration temperature was observed for dihydrate. These results suggest that the influence of grinding on thermal behavior was different for the two hydrates.
