Authors:U. Griesser, M. Szelagiewicz, U. Hofmeier, C. Pitt, and S. Cianferani
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.
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.
Authors:J May, A Del Grosso, N Etz, R Wheeler, and L Rey
(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
Authors:Ana Paula Barreto Gomes, Fátima Duarte Freire, and Cícero Flávio Soares Aragão
well as measurement of the vaporpressure 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 vaporpressure of the
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)
(n=3, 4 and 5). The vapor pressures of
the cadmium (pCd)
and trimer (p(MoO3)3)
measured in the temperature range 987≤T/K≤1111
could be expressed, respectively, as ln (pCd/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:
(s)0= –1002.0+0.267T14.5 kJ mol–1
(987≤T/K≤1033) and fGCdMoO4 (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
Authors:N. Morozova, P. Semyannikov, S. Trubin, P. Stabnikov, A. Bessonov, K. Zherikova, and I. Igumenov
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 ΔHT* and entropy ΔST0 were determined. The energy of intermolecular interaction in the crystals of complexes was calculated.
Authors:G. I. Zharkova, S. V. Sysoev, P. A. Stabnikov, V. A. Logvinenko, and I. K. Igumenov
dependence of the saturated vaporpressure 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
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.
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.
The Modified Entrainment Method developed by Faktor et al.  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.