Ultraviolet photoelectron spectroscopy indicates that butadiene adsorbs molecularly onto Mo(100) at 120-150 K. The occupied molecular orbitals are only minimally perturbed on adsorption, and work function measurements indicate that bonding to the surface is by electron donation from the metal to the adsorbed butadiene. Both near-edge X-ray absorption fine-structure measurements and angle-resolved photoelectron spectroscopy indicate that the molecular plane of butadiene is oriented at ~40°to the metal surface. Warming a butadiene-covered surface to 200 K results in the thermal transformation of chemisorbed butadiene to a different surface species exhibiting a photoelectron spectrum that corresponds well to that of gas-phase írcms-2-butene. This observation is in accord with theoretical predictions that suggest that the middle C-C bond of butadiene should be strengthened relative to the terminal C-C bonds on chemisorption.
Development of an appropriate dissolution method for quality control purposes requires consideration of many factors and a balance of different needs. The method is typically distinctive to each drug product because of the unique characteristics of the active ingredient, the formulation, and the manufacturing process. The method development and selection process remains subjective due to the potential range of profiles that could be considered acceptable. This article presents a strategy and detailed recommendations for developing a quality control dissolution method for immediate-release solid oral dosage forms for the purpose of quality control and formulation or process development. The strategy is developed based on an understanding of dissolution technology, regulatory expectations, literature, and experiences in developing various dissolution methods. A case study demonstrating this strategy with the discriminatory potential of an appropriately developed dissolution method is also described.
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