A general review of the methods available for the physical characterization of pharmaceutical solids is presented. The techniques are classified as being on the molecular level (properties capable of being detected in an ensemble of individual molecules), the particulate level (properties which can be detected through the analysis of an ensemble of particles), and the bulk level (properties which can be measured only using a relatively large amount of material). The molecular-level properties discussed are infrared spectroscopy and nuclear magnetic resonance spectrometry, the particulate-level properties discussed are particle morphology, particle size distribution, powder X-ray diffraction, and thermal methods of analysis, and the bulk-level properties discussed are surface area, porosity and pore size distribution, and powder flow characteristics. Full physical characterization of three modifications of lactose (hydrous, anhydrous, and Fast-Flo) is presented to illustrate the type of information which can be obtained using each of the techniques discussed.
It has been found that the current NF identity test for microcrystalline cellulose is actually an assay of the response of the material to energy dissipation expended during the analysis procedure. The blending step needed to effect suspension of the material results in a disintegration of the microcrystalline particles and a concomitant increase in the viscosity of the slurry viscosity. These effects were shown not to be unique functions of either blender speed or blending time. The passage or failure of a given sample of microcrystalline cellulose under the conditions of the identity test was found to be a consequence of the test conditions used. Any given sample of microcrystalline cellulose can be made to pass the identity test if it is blended for a sufficiently long time or at a sufficiently high speed. The test is sufficient, however, to differentiate powdered cellulose from powdered cellulose.
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