Differential scanning calorimetry purity analysis

Thermal methods have found extensive use in the past as part of a program of preformulation studies, since carefully planned work can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [2], It should be noted, however, that the use of differential scanning calorimetry (DSC) for such work is less in vogue than it used to be. Nevertheless, in appropriately designed applications, thermal methods of analysis can be used to evaluate compound purity,... 

In most cases, the purity of a pharmaceutical substance is determined by comparison of the reference standard with the known purity assigned. On the other hand, when no reference standard sample is available, the purity is determined by an absolute method in which the calculated result is based on theory and not by a comparative method. Purity established by analytical methods such as phase-solubility analysis or differential scanning calorimetry (DSC) is known as absolute purity (Figs. 3 and 4). 

High-purity materials are available as pure solids for chemical uses such as metals used as reference substances for metallurgical analysis, and compounds used as primary standards for many types of titrimetry, and as standards for elemental microanalysis. Other available high-purity substances intended for diverse physical properties include ion activity standards for the calibration of pH and ion-selective electrodes standards for various thermodynamic uses including melting point determinations, differential scanning calorimetry and bomb calorimetry and standards for the calibration of spectrophotometers. 

Thermal analysis gives information on the fundamental behavior and structure of materials based on their thermochemical and thermophysical properties. Differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetry (TG), dilatometry, and other related dynamic thermal methods serve as analytical tools for characterizing a wide variety of solid materials. Information obtainable by these methods includes phase relationships, identification and measurement of impurities in high-purity materials, fingerprint identifications, thermal histories of the material, and dissociation pressures. 

---