ADSORPTION OF WATER ON CYCLOSPORINE-A, FROM ZERO TO FINITE SURFACE COVERAGE

A gas-chromatographic technique was used to measure the adsorption of water at zero and finite surface coverage of the orthorhombic form of cyclosporin A. For calculation of the surface area, the BET adsorption isotherms of water at 373 K and nitrogen at 77 K were utilized. When nitrogen was used as adsorbate a lower value for the specific surface area was obtained. This could be explained in terms of the size and shape of the adsorbate molecule and its ability to access the internal surface of the adsorbent. Results obtained with the scanning electron microscope revealed small apertures on the adsorbent surface.