Application of modulated-temperature DSC to the analysis of enantiotropically related polymorphic transitions

Modulated-temperature DSC analysis of enantiotropically-related polymorphic transitions are presented. The transitions of furosemide and tolbutamide were detected by endothermic peaks as have been reported in literature. However, those peaks were reproduced only in the reversible heat flow, suggesting that there were no enthalpy jumps during the transitions. These polymorphic transitions were attributed to of the second-order. In the case of sulfamerazine, the transition peak could be explained mainly by the enthalpy jump. This transition was elucidated as being of the first-order. Some enantiotropically related polymorphs are known to be kinetically reversible, while others are not. This difference can most likely be explained by the difference in the order of the transition. The applicability of fractal analysis for quantifying the disorder of the Lissajous figure is also discussed.