Determination of surface heterogeneity of D-mannitol by sessile drop contact angle and finite concentration inverse gas chromatography.


The sensitivity of two techniques in tracking changes in surface energetics was investigated for a crystalline excipient, D-mannitol. Macroscopic crystals of D-mannitol were grown from saturated water solution by slow cooling, and sessile drop contact angle was employed to measure the anisotropic surface energy. The facet-specific surface energy was consistent with localised hydroxyl group concentrations determined by X-ray photoelectron spectroscopy (XPS), and was also in excellent agreement with the surface energy distribution of the powder form of mannitol measured via a new methodology using inverse gas chromatography (IGC) at finite concentrations. The gamma(SV)(d) was found to vary between 39.5 mJ/m(2) and 44.1 mJ/m(2) for contact angle and between 40 mJ/m(2) and 49 mJ/m(2) for IGC measurements. We report here, a high level of surface heterogeneity on the native mannitol crystal surfaces. When the surfaces of both D-mannitol samples (powder and large single crystals) were modified by dichlorodimethylsilane to induce surface hydrophobicity, both IGC and contact angle revealed a homogeneous surface due to functionalisation of mannitol crystal surface with methyl groups resulting in gamma(SV)(d) of approximately 34 mJ/m(2). It was shown that both IGC and contact angle techniques are able to detect surface chemical variations and detailed surface energetic distribution.

DOI: 10.1016/j.ijpharm.2009.12.011
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@article{Ho2010DeterminationOS, title={Determination of surface heterogeneity of D-mannitol by sessile drop contact angle and finite concentration inverse gas chromatography.}, author={Raimundo Ho and Steven J. Hinder and John F. Watts and Sarah E Dilworth and Daryl R. Williams and Jerry Y Y Heng}, journal={International journal of pharmaceutics}, year={2010}, volume={387 1-2}, pages={79-86} }