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Investigation of solid-state reactions using variable temperature X-ray powder diffractometry. II. Aminophylline
Suneel K Rastogi1, Marek Zakrzewski, Raj Suryanarayanan
1College of Pharmacy, University of Minnesota, Minneapolis 55455, USA.
Pharmaceutical Research
|October 31, 2002
Summary
X-ray powder diffractometry (XRD) enables simultaneous quantification of multiple solid phases, offering a powerful method to study complex pharmaceutical reaction kinetics and determine activation energies.
Area of Science:
- Solid-state chemistry
- Pharmaceutical sciences
- Crystallography
Background:
- Pharmaceutical solid-state reactions involve complex transformations.
- Understanding reaction kinetics is crucial for drug stability and formulation.
- Simultaneous quantification of multiple phases is often challenging.
Purpose of the Study:
- To demonstrate the utility of X-ray powder diffractometry (XRD) for studying pharmaceutical solid-state reaction kinetics.
- To simultaneously quantify reactant, intermediate, and product phases during a reaction.
Main Methods:
- Aminophylline monohydrate decomposition was studied isothermally (65-100°C).
- X-ray powder diffractometry (XRD) measured intensities of unique peaks for each phase.
- Kinetic data were fitted to derived equations to determine rate constants.
Main Results:
- First-order kinetics were assumed for reaction steps.
- Rate constants and activation energies were determined from Arrhenius plots.
- Intermediate phase concentration varied with temperature, indicating different kinetic dependencies.
Conclusions:
- Variable temperature XRD is effective for probing reaction kinetics in crystalline pharmaceuticals.
- The method allows simultaneous quantification of multiple solid phases.
- XRD provides valuable insights into complex solid-state transformations.