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Abstract  

Isothermal microcalorimetry was used to evaluate excipient compatibility of solid dosage form. Oxybutynin hydrochloride and cefaclor were used as model drugs for compatibility test with excipients. The calorimetric data for compatibility test were compared with those of HPLC data. Evaluation of compatibility between drug and excipient of solid dosage form might be possible to use isothermal microcalorimetry instead of conventional method. By using microcalorimetric method, the evaluation of the compatibility between drug and excipient could be successfully performed with a simple operation in a short time. The application of the isothermal microcalorimetry would be useful for the screening test of the drug compatibility with excipients.

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In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After ∼10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.

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Abstract  

A series of blends of dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PANDR) and PVC were synthesized by solution blending technique and investigated by heatflow microcalorimetry (HFC) for thermal and oxidative stability and for PVC–PANDR compatibility. FTIR results provided evidence for strong dipole–dipole interactions between PANDR and PVC. The energy of the oxidation is independent of the composition. The interaction energy and thermal stability increased with the increase of PANDR content in the blend. The activation energies calculated by using Arrhenius relationship can be employed for accelerated ageing of the synthesized blends. It has been observed that the average degradation of PANDR component is higher than that of PVC.

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Abstract  

The exothermic decomposition of cumene hydroperoxide (CHP) in cumene liquid was characterized by isothermal microcalorimetry, involving the thermal activity monitor (TAM). Unlike the exothermic behaviors previously determined from an adiabatic calorimeter, such as the vent sizing package 2 (VSP2), or differential scanning calorimetry (DSC), thermal curves revealed that CHP undergoes an autocatalytic decomposition detectable between 75 and 90°C. Previous studies have shown that the CHP in a temperature range higher than 100°C conformed to an n th order reaction rate model. CHP heat of decomposition and autocatalytic kinetics behavior were measured and compared with previous reports, and the methodology and the advantages of using the TAM to obtain an autocatalytic model by curve fitting are reported. With various autocatalytic models, such as the Prout-Tompkins equation and the Avrami-Erofeev rate law, the best curve fit among models was also investigated and proposed.

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Abstract  

The amorphous content of different Desferal samples was quantified by recording its recrystallization using isothermal microcalorimetry in a static as well as in a flowing humid atmosphere. Furthermore water vapor sorption gravimetry was performed for the same purpose. These analytical methods result in a quantitative signal directly dependent on the content of the amorphous phase (recrystallization, water sorption equilibrium). Their sensitivity allows the detection of amorphous content below 1%. Methods are compared and advantages and disadvantages are discussed.

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Abstract  

A well-known photolabile substance, nifedipine, was used as a sample material to test self-constructed irradiation cells and demonstrate their usefulness in photostability studies. The devices were made as accessories for a commercial isothermal microcalorimeter. Several powder samples containing various amounts of moisture were irradiated with monochromatic light as a scan measurement from 700 to 280 nm, and the heat flow evolved in the photodegradation of nifedipine was determined. According to the results, light does not affect the nifedipine molecule directly, but the photodegradation is a result of the combined effects of moisture and light.

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The adsorption of argon, oxygen, nitrogen and carbon monoxide at 77 K on crystalline zirconia and microporous zirconia gels has been studied by adsorption volumetry and isothermal microcalorimetry.

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