The observed rate of drug release from a polymeric drug delivery system is governed by a combination of diffusion, swelling and erosion. It is thus not a simple task to determine the effects of the polymer on the observed drug release rate, because the swelling characteristics of the polymer are inferred from the drug release profile. Here we propose to use solution calorimetry to monitor swelling. Powdered polymer samples (HPMC E4M, K4M, K15M and NaCMC, both alone and in a blend) were dispersed into water or buffer (pH 2.2 and 6.8 McIlvaine citrate buffers) in a calorimeter and the heat associated with the swelling phenomena (hydration, swelling, gelation and dissolution) was recorded. Plots of normalised cumulative heat (i.e. qt/Q, where qt is the heat released up to time t and Q the total amount of heat released) versus time were analysed by the power law model, in which a fitting parameter, n, imparts information on the mechanism of swelling.
For all systems the values of n were greater than 1, which indicated that dissolution occurred immediately following hydration of the polymer. However, while not suitable for determining reaction mechanism, the values of n for each polymer were significantly different and, moreover, were observed to vary both as a function of particle size and dissolution medium pH. Thus, the values of n may serve as comparative parameters. Properties of the polymer blends were observed to be different from those of either constituent and correlated with the behaviour seen for polymer tablets during dissolution experiments. The data imply that solution calorimetry could be used to construct quantitative structure–activity relationships (QSARs) and hence to optimise selection of polymer blends for specific applications. 相似文献
A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating
parameters and particle collection mechanisms on the synthesis of CeO2 particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor
regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating
conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO2 particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels
(alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature
of CeO2 formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were
taken using a fast speed CCD camera. 相似文献
The present paper describes stability indicating reverse phase high-performance liquid chromatography (RP-HPLC) assay method
for nitazoxanide in bulk drugs. The developed method is also applicable for the related substances determination in bulk drug.
The drug substance was subjected to stress conditions of hydrolysis, photolysis and thermal degradation. The considerable
degradation of nitazoxanide was observed under base and peroxide hydrolysis. The drug was found to be stable in other stress
conditions attempted. The chromatographic separation of the drug was achieved on reversed-phase C-18 column. Eluents were
monitored on photo-diode array detector at a wavelength of 240 nm. The mobile phase was aqueous 0.005 M tetra butyl ammonium
hydrogen sulphate and acetonitrile (45:55, v/v). In the developed HPLC method, resolution between nitazoxanide and its potential impurities, namely Imp-A (5-nitro-1,3-thiazol-2-amine),
Imp-B (N-(5-nitro-1,3-thiazol-2-yl) acetamide) and Imp-C (2-{[(5-nitro-1,3-thiazol-2-yl) amino] carbonyl} phenyl 2-(acetyloxy) benzoate)
was found greater than three. The developed RP-HPLC method was validated with respect to response function, accuracy, precision,
specificity, stability of analytical solutions and robustness. Also to determine related substances and assay determination
of nitazoxanide that can be used to evaluate the quality of regular production samples. The developed method can also be conveniently
used for the assay determination of nitazoxanide in pharmaceutical formulations. 相似文献
Summary. In this work was presented an application of the use of task specific onium salts (TSOSs) as soluble supports in Grieco’s multicomponent synthesis of tetrahydroquinolines. These soluble supports are of wide applicability and combine advantages
of solid phase synthesis without its limitations with those of solution phase chemistry. After a simple washing step, products
were cleaved from the supports and obtained in pure form and good yields. 相似文献