Crystallinity and Polymorphism

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are the techniques most widely used for the characterization of crystallinity and polymorphism of solid lipid particles. Although DSC is usually more sensitive in detecting crystalline material, XRD is much more reliable in determining the type of polymorph present in the dispersions because it provides structural data. In contrast, DSC can detect the type of polymorph only indirectly via the transition temperatures and enthalpies. Because these parameters may be different from those observed in the bulk material, particularly for small colloidal particles [1,62], assigmnent of polymorphic forms in DSC curves should be supported by x-ray data. 

Fig. 10.3. Strategic role of Raman in process monitoring and control of crystallinity and polymorphism...

Crystallinity and polymorphism X-ray powder diffraction Differential scanning calorimetry (DSC) Infiared spectroscopy Solid state NMR Raman spectroscopy Thermogravimetric analysis (TGA)... 

In summary, the degree of crystallinity and polymorphic form can be important factors for tableting and care must be taken to ensure that the materials used have consistent crystallinity. Unfortunately, there are no absolute rules to enable the prediction of tableting behavior based on knowledge of a material s crystallinity so data must be considered on a case-by-case basis. 

In the case of pharmaceutical samples, Raman spectroscopy is sensitive to crystallinity and polymorphism, both of which are important with regards to the bioavailability (and protection of the intellectual property) of active ingredients. 

Solubility in aqueous and organic Crystalline and polymorphic forms solvents Solvation and hydration... 

Thermal analysis is an extremely important analytical tool for the pharmaceutical industry. All transitions in materials involve the flow of heat (either into the sample during an endothermic event or out of the sample during an exothermic event) and DSC is the universal detector for measuring a wide variety of transitions in pharmaceutical materials. These include measurement of amorphous structure, crystallinity (and polymorphs), drug-excipient interaction and many other applications. 

Calorimetric analysis by DSC provides information on the melting temperature, crystallization, enthalpy, polymorphic transition, and degree of crystallinity of the particles. XRD, on the other hand, also evaluates the crystallinity and polymorphic transition events that may eventually occur in microparticles. 

Ogawa, K. 1991. Effect of heating an aqueous suspension of chitosan on the crystallinity and polymorphs. 

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