Sacchetti Mark
GlaxoSmithKline, Pharmaceutical Development, Research Triangle Park, NC 27709, USA.
Pharm Dev Technol. 2006;11(3):351-8. doi: 10.1080/10837450600769793.
A complete nitrogen adsorption isotherm was measured for alpha-lactose monohydrate, from 0.001 to 0.995 relative pressure at 77 K. The isotherm was qualitatively classified as Type II, and was quantitatively analyzed for surface area, porosity, and surface heterogeneity. Surface area results revealed that the normal Brunauer Emmett Teller (BET) range of 0.05-0.35 relative pressure was not suitable for this grade of lactose, but having full isotherm data enabled a more appropriate analytical range to be found, illustrating the importance of measuring the entire isotherm as an essential step in method development. The isotherm was analyzed for micro and mesoporosity, both of which were found to be insignificant for lactose. The low relative pressure range 0.001-0.005 did not obey Henry's law, indicating the presence of surface heterogeneity. Density functional theory was exploited to quantitatively measure heterogeneity in the surface energy of lactose, using the full nitrogen adsorption profile. As expected for a crystalline material with multiple faces and likely presence of imperfections on the surface, the surface energy distribution function was broad with more than one mode.
在77 K下，测量了α-乳糖一水合物在相对压力为0.001至0.995范围内的完整氮吸附等温线。该等温线定性地归类为II型，并对其表面积、孔隙率和表面非均质性进行了定量分析。表面积结果表明，相对压力在0.05 - 0.35的正常布鲁诺尔-埃米特-特勒（BET）范围不适用于该等级的乳糖，但完整的等温线数据使得能够找到更合适的分析范围，这说明了测量整个等温线作为方法开发中关键步骤的重要性。对该等温线的微孔和介孔进行了分析，发现两者对乳糖来说都不显著。相对压力范围在0.001 - 0.005时不遵循亨利定律，表明存在表面非均质性。利用密度泛函理论，通过完整的氮吸附曲线来定量测量乳糖表面能的非均质性。正如对具有多个面且表面可能存在缺陷的晶体材料所预期的那样，表面能分布函数很宽且有不止一个峰。
