Surface analysis of griseofulvin powders by krypton adsorption: Evaluation of specific surface area, BET constant C and polanyi adsorption potential

Abstract

The use of krypton for the analysis of the surface properties of three reference standards and 18 samples of griseofulvin was assessed. A strong correlation (r = 0.9984) was observed between the Brunauer, Emmett and Teller (BET) specific surface areas (S) determined using krypton (S Kr ) and those using nitrogen (S N ). For low sample area (< 0.27 m 2), the estimations of S Kr were more accurate than those of S N . The cross-sectional area of adsorbed krypton, calculated in relation to nitrogen, is independent of the nature of the adsorbents, i.e., is not a function of the BET C constants, determined using krypton adsorption (C Kr ). The values of C Kr were related to the particle morphology. Moreover, the change of surface property upon heat treatment was reflected in a three-fold increase of C Kr . A linear correlation between the Polanyi adsorption potential and ln C Kr was observed suggesting that the entropy of adsorption is either constant or is a linear function of the enthalpy of adsorption. The results support the use of krypton adsorption as a technique of choice that provides valuable information concerning the surface of powders which, in many cases, is difficult to obtain using other experimental procedures.