Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9918698 | International Journal of Pharmaceutics | 2005 | 11 Pages |
Abstract
Solution calorimeters are based on semi-adiabatic or isothermal heat-conduction principles and differ in the way they record data. They also have different measuring sensitivities and require different quantities of solute and solvent. As such, the choice of chemical test substance is not straightforward. Usually the dilution of KCl is recommended; it is possible to purchase a reference sample of KCl that has a certified enthalpy of solution and this standard material is usually used to test semi-adiabatic instruments. Here, we review the suitability of a range of chemical test substances (KCl, sucrose and Tris) for an isothermal heat-conduction solution calorimeter. It was found that KCl was not the best test material because its relatively high enthalpy of solution (ÎsolH) necessitated the use of small samples (2 mg), resulting in a relatively large standard deviation (Ïn â 1) in the values recorded (ÎsolH = 17.14 ± 0.49 kJ molâ1); furthermore, KCl data must be corrected to account for the effect of dilution, although the correction was found to be small (0.07 kJ molâ1) under the experimental conditions employed here. Sucrose appears to be a much more robust test material for isothermal heat-conduction instruments because its lower enthalpy of solution allows the use of much larger samples (20 mg), which minimises experimental errors. The ÎsolH value returned (6.14 ± 0.08 kJ molâ1) is in excellent agreement with the literature. It is also cheap, readily available and requires minimal preparation although its widespread use would require the preparation of a certified reference sample.
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Authors
Rita Ramos, Simon Gaisford, Graham Buckton, Paul G. Royall, Barbara T.S. Yff, Michael A.A. O'Neill,