Application Note: The characterisation of polymorphs by thermal analysis

TGA-FTIR was used to characterize and distinguish between different polymorphs…

If two polymorphic forms of a solid are present, whereby one form melts and the other sublimes or vaporizes at about the same temperature, then evolved gas analysis can be used to obtain quantitative (mass loss) and qualitative (spectral) data to analyse such solids.

The two pharmaceutically important compounds shown in Figure 1, the active pharmaceutical ingredient (API) venlafaxine hydrochloride and the well-known host material 1,1-bis (4-hydroxyphenyl)cyclohexane, were analysed by DSC, TGA, hotstage microscopy (HSM) and TGA-FTIR to study the phase transitions that occur on heating. A substance is said to exhibit polymorphism if it can exist in two or more crystal lattice forms. These are called polymorphs and have different physical properties.