Study Methods

At the preformulation stage, the limitations of the quantity of the sample available determines to a great degree the type of study to be conducted. Some physical properties are fundamental in nature, whereas others are a manifestation of these basic properties. For example, melting point determination reveals much about the internal structure of crystals, the solubility and dissolution characteristics; the latter properties are the derived properties. As a result, techniques available to study the aforementioned properties are categorized by the U.S. FDA in a decreasing order of importance (FDA, The Gold Sheet, 1985). The following is an expanded list of these methodologies available for evaluation:

• thermal analytical techniques [e.g., DSC, differential thermal analysis (DTA), TGA, and the like]

• solid-state Raman spectroscopy

• crystalline index of refraction

• phase solubility analysis

• solution pH profile determination

• solution calorimetry

• comparative intrinsic dissolution rates

• cross-polarization/magic angle spinning (CP/MAS) solid-state NMR

• hygroscopicity measurement (particularly for salts)

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