Unusual effect of water vapor pressure on dehydration of dibasic calcium phosphate dihydrate.
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| Abstract |
Dibasic calcium phosphate occurs as an anhydrate (DCPA; CaHPO₄) and as a dihydrate (DCPD; CaHPO₄•2H₂O). Our objective was to investigate the unusual behavior of these phases. Dibasic calcium phosphate dihydrate was dehydrated in a (i) differential scanning calorimeter (DSC) in different pan configurations; (ii) variable-temperature X-ray diffractometer (XRD) at atmospheric and under reduced pressure, and in sealed capillaries; and (iii) water vapor sorption analyzer at varying temperature and humidity conditions. Dehydration was complete by 210°C in an open DSC pan and under atmospheric pressure in the XRD. Unlike "conventional" hydrates, the dehydration of DCPD was facilitated in the presence of water vapor. Variable-temperature XRD in a sealed capillary and DSC in a hermetic pan with pinhole caused complete dehydration by 100°C and 140°C, respectively. Under reduced pressure, conversion to the anhydrate was incomplete even at 300°C. The increase in dehydration rate with increase in water vapor pressure has been explained by the Smith-Topley effect. Under "dry" conditions, a coating of poorly crystalline product is believed to form on the surface of particles and act as a barrier to further dehydration. However, in the presence of water vapor, recrystallization occurs, creating cracks and channels and facilitating continued dehydration.
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| Authors | Aditya M Kaushal, Venu R Vangala, Raj Suryanarayanan |
| Journal | Journal of pharmaceutical sciences (J Pharm Sci) Vol. 100 Issue 4 Pg. 1456-66 (Apr 2011) ISSN: 1520-6017 [Electronic] United States |
| PMID | 24081471 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't) |
| Copyright | Copyright © 2010 Wiley-Liss, Inc. |
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