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Abstract  

In order to determine the applicability of vapor pressure studies on polymorphic modifications, pairs of enantiotropically related modifications of caffeine, theophylline and carbamazepine were investigated. The studies were performed over a wide temperature range (71 to 191°C) and accordingly over a wide vapor pressure range (0.02 to 400 Pa) using an automatic instrument constructed on the basis of the gas saturation principle. This instrument enables an analytical determination of the main component and the impurities present by the chromatographic separation of the substances transported in the gas flow. Therefore, the real partial pressure of the main component can be measured. Due to the high precision of the applied method it was possible to determine partial pressure curves and the thermodynamic transition temperature — the point at which the vapor pressure of two crystal polymorphs is equal. The thermodynamic transition temperatures of caffeine and theophylline were determined to be 136 and 232°C, respectively. These values are in agreement with experimental or calculated values derived from DSC investigations but are more reliable. Vapor pressure measurements of carbamazepine are only meaningful in the low temperature range due to its decomposition at high temperatures. The thermodynamics, advantages and limits of vapor pressure determinations of polymorphic modifications are discussed.

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Abstract  

A simplified approach was developed to estimate the vapor pressure of pure compounds from experimental data obtained by isothermal thermogravimetric (TG) analysis. A numerical procedure was developed to estimate the Antoine parameters of the substance by the analysis of isothermal TG data. The results of the experimental validations carried out evidenced that at least a preliminary estimation of vapour pressures of pure substances by the analysis of TG data is possible. The limited time and the reduced amounts of sample required for the experimental runs make the technique attractive with respect to the conventional and more accurate techniques for vapor pressure assessment.

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Thermogravimetry and vapor pressure moisture

Applications to determination of residual moisture in BCG vaccine

Journal of Thermal Analysis and Calorimetry
Authors: J May, A Del Grosso, N Etz, R Wheeler, and L Rey

Abstract  

Thermogravimetry (TG), thermogravimetry/mass spectrometry (TG/MS), and loss-on-drying methodology are used to provide residual moisture results for freeze-dried biological products regulated by the US Food and Drug Administration. Residual moisture specifications must be met in order to ensure freeze-dried biological product potency and stability throughout the licensed product's shelf life. TG, TG/MS, loss-on-drying and vapor pressure moisture measurements are compared for a BCG Vaccine. Comparisons are made between residual moisture data for the freeze-dried cake and vapor pressure moisture determinations in the space above the freeze-dried cake in the final container. Vapor pressure moisture precision data is presented for α-interferon and BCG vaccine. Impact of residual moisture and vapor pressure moisture upon product stability is presented.

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well as measurement of the vapor pressure of substances [ 16 – 24 ]. Evaporation can be stated as the transition from the liquid phase to the vapor phase, without a change in chemical composition. Several factors such as vapor pressure of the

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Abstract  

Thermodynamic stability of CdMoO4 was determined by measuring the vapor pressures of Cd and MoO3 bearing gaseous species. Th vaporization reaction could be described as CdMoO4(s)+MoO2(s) =Cd(g)+2/n(MoO3)n (n=3, 4 and 5). The vapor pressures of the cadmium (p Cd) and trimer (p (MoO3)3) measured in the temperature range 987≤T/K≤1111 could be expressed, respectively, as ln (p Cd/Pa) = –32643.9/T+29.460.08 and ln(p (MoO3)3/Pa) = –32289.6/T+29.280.08. The standard molar Gibbs free energy of formation of CdMoO4(s), derived from the vaporization results could be expressed by the equations: f G CdMoO4 (s) 0= –1002.0+0.267T14.5 kJ mol–1 (987≤T/K≤1033) and f G CdMoO4 (s) 0 = –1101.9+0.363T14.4 kJ mol–1 (1044≤T/K≤1111). The standard enthalpy of formation of CdMoO4(s) was found to be –1015.414.5 kJ mol–1 .

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Abstract  

Volatile compounds of iridium(I): (acetylacetonato)(1,5-cyclooctadiene)iridium(I) Ir(acac)(cod), (methylcyclopentadienyl) (1,5-cyclooctadiene)iridium(I) Ir(Cp’)(cod), (pentamethylcyclopentadienyl)(dicarbonyl) iridium(I) Ir(Cp*)(CO)2 and (acetylacetonato)(dicarbonyl)iridium(I) Ir(acac)(CO)2 were synthesized and identified by means of element analysis, NMR-spectroscopy, mass spectrometry. Thermal properties in solid phase for synthesized iridium(I) complexes were studied by means of thermogravimetric analysis in inert atmosphere (He). By effusion Knudsen method with mass spectrometric registration of gas phase composition the temperature dependencies of saturated vapor pressure were measured for iridium(I) compounds and the thermodynamic characteristics of vaporization processes enthalpy ΔH T* and entropy ΔS T 0 were determined. The energy of intermolecular interaction in the crystals of complexes was calculated.

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dependence of the saturated vapor pressure was measured by the flow method and the standard thermodynamic parameters Δ H T and Δ S T o were determined for the vaporization process of the compounds. The molecule packing in the crystals was considered using

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Abstract  

For a large number of DSC calibration substances the vapour pressure at room temperature or at transition temperature (whichever is the highest) is given. It is important to know the vapour pressure of substances, because a DSC measurement on a substance with a high vapour pressure requires encapsulation of the substance in a hermetically sealed crucible to prevent evaporation. Because the calibration procedure must be performed using the same type of sample pan as will be used during the actual measurements, the presented information allows one to decide which calibration substances and/or what type of sample pan should be used for calibration.

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Abstract  

A new pressure DSC module (Mettler DSC27HP) and its abilities for vapor pressure determination in the range of subambient pressure to 7 MPa are presented. To compare the new to an established method, vapor pressures of caffeine, naphthalene and o-phenacetin have been determined both by pressure DSC and the Knudsen effusion cell method. These results, including the derived heats of evaporation and heats of sublimation, are compared to literature values.

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Abstract  

The Modified Entrainment Method developed by Faktor et al. [1] is an attractive yet not very popular method to determine vapour pressures in the range of 0.002 to 0.1 bar at 10–1000°C. The method consists of evaporating a solid or liquid from a small bulb through a capillary into a flowing inert gas, e.g. argon. The vapour pressure of the sample is related to the rate of evaporation and some easily controlled experimental parameters. In the present paper a new convenient experimental set-up is described and its use to study the decomposition of metal complexes is illustrated.

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