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Title: Effect of milling on DSC thermogram of excipient adipic acid
Authors: Ng, W.K.
Kwek, J.W.
Yuen, A.
Tan, C.L.
Tan, R. 
Keywords: DSC
Fusion enthalpy
Melting temperature
Issue Date: Mar-2010
Citation: Ng, W.K., Kwek, J.W., Yuen, A., Tan, C.L., Tan, R. (2010-03). Effect of milling on DSC thermogram of excipient adipic acid. AAPS PharmSciTech 11 (1) : 159-167. ScholarBank@NUS Repository.
Abstract: The purpose of this research was to investigate why and how mechanical milling results in an unexpected shift in differential scanning calorimetry (DSC) measured fusion enthalpy (Δfus H) and melting point (Tm) of adipic acid, a pharmaceutical excipient. Hyper differential scanning calorimetry (hyper-DSC) was used to characterize adipic acid before and after ball-milling. An experimental study was conducted to evaluate previous postulations such as electrostatic charging using the Faraday cage method, crystallinity loss using powder X-ray diffraction (PXRD), thermal annealing using DSC, impurities removal using thermal gravimetric analysis (TGA) and Karl Fischer titration. DSC thermograms showed that after milling, the values of ΔfusH and Tm were increased by approximately 9% and 5 K, respectively. Previous suggestions of increased electrostatic attraction, change in particle size distribution, and thermal annealing during measurements did not explain the differences. Instead, theoretical analysis and experimental findings suggested that the residual solvent (water) plays a key role. Water entrapped as inclusions inside adipic acid during solution crystallization was partially evaporated by localized heating at the cleaved surfaces during milling. The correlation between the removal of water and melting properties measured was shown via drying and crystallization experiments. These findings show that milling can reduce residual solvent content and causes a shift in DSC results. © 2010 American Association of Pharmaceutical Scientists.
Source Title: AAPS PharmSciTech
ISSN: 15309932
DOI: 10.1208/s12249-009-9372-5
Appears in Collections:Staff Publications

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