Use of sorption isotherms to study the effect of moisture on the hardness of aged compacts

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Abstract
Hardness changes in aged compacts of the salts of sodium, potassium and ammonium were studied at various humidities. The anionic and cationic effects on tablet hardening were determined from sorption isotherms of the salts. The sorption isotherms were obtained by inverse gas chromatography. The isosteric heats of adsorption were calculated from isotherms measured at temperatures from 40–60°C. The heat of sorption was highest for the chloride salt, intermediate for the bromide salt, and the least for the iodide salt. Potassium chloride attained the highest hardness increase while the iodide salt experienced the least hardness increase. The cationic effect was also rationalized from the heat of sorption data.