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Quantitative characterization of adsorption isotherms using isothermal microcalorimetry
M Pudipeddi1, T D Sokoloski, S P Duddu
1School of Pharmacy, University of Wisconsin, Madison 53706, USA.
Journal of Pharmaceutical Sciences
|April 1, 1996
Summary
This study introduces a novel calorimetric method to measure water adsorption on solids like sodium benzoate. The technique accurately determines surface area and monolayer capacity, offering a sensitive alternative to traditional methods.
Area of Science:
- Physical Chemistry
- Materials Science
- Surface Science
Background:
- Characterizing solid material surface properties is crucial for applications in pharmaceuticals and materials science.
- Conventional methods like gas adsorption (BET analysis) are widely used but can be time-consuming and require specialized equipment.
- Microcalorimetry offers a potentially more sensitive and convenient alternative for adsorption studies.
Purpose of the Study:
- To determine the integral heat of adsorption of water vapor on sodium benzoate using microcalorimetry.
- To develop and validate a modified BET equation relating heat evolved during adsorption to partial pressure.
- To assess the utility of isothermal microcalorimetry for calculating monolayer capacity and surface area.
Main Methods:
- Integral heat of adsorption measurements using a heat conduction microcalorimeter.
- Application of a modified BET equation to calorimetric adsorption data.
- Comparison of results with conventional gravimetric and volumetric adsorption data.
Main Results:
- A calorimetric equation was developed to describe heat evolved during water vapor adsorption as a function of relative humidity.
- The modified BET equation successfully described the calorimetric isotherm shape and allowed calculation of monolayer capacity.
- Calculated surface area values from microcalorimetry data showed good agreement with conventional methods.
Conclusions:
- Isothermal microcalorimetry provides a sensitive and convenient method for determining the water adsorption surface area of solid materials.
- The developed model and method are effective for characterizing adsorption properties, comparable to traditional techniques.
- This approach is valuable for comparing surface properties of pharmaceutical ingredients and excipients.