Thermal analysis solubility

Of all the methods available for the physical characterization of solid materials, it is generally agreed that crystallography, microscopy, thermal analysis, solubility studies, vibrational spectroscopy, and nuclear magnetic resonance are the most useful for characterization of polymorphs and solvates. However, it cannot be overemphasized that the defining criterion for the existence of polymorphic types must always be a non-equivalence of crystal structures. For compounds of pharmaceutical interest, this ordinarily implies that a non-equivalent X-ray powder diffraction pattern is observed for each suspected polymorphic variation. All other methodologies must be considered as sources of supporting and ancillary information, but cannot be taken as definitive proof for the existence of polymorphism by themselves. 

It is important to ascertain whether the solid phase of the solute changes during equilibration to produce a different polymorph or solvate, by analyzing the solid phase (using either chemical or thermal analysis, or x-ray diffraction). If a solid-solid phase transition occurs during equilibration, the measured equilibrium solubility will be that of the new solid phase of the solute. Methods of circumventing this problem have been proposed and evaluated [26]. 

Widespread medicinal use of colloidal bismuth subcitrate (CBS) has prompted extensive studies of bismuth compounds involving the citrate anion. Bismuth citrate is essentially insoluble in water, but a dramatic increase in solubility with increasing pH has been exploited as a bio-ready source of soluble bismuth, a material referred to as CBS. Formulation of these solutions is complicated by the variability of the bismuth anion stoichiometry, the presence of potassium and/ or ammonium cations, the susceptibility of bismuth to oxygenation to Bi=0, and the incorporation of water in isolated solids. Consequently, a variety of formulas are classified in the literature as CBS. Solids isolated from various, often ill-defined combinations of bismuth citrate, citric acid, potassium hydroxide, or ammonium hydroxide have been assigned formulas on the basis of elemental analysis data or by determination of water and ammonia content, but are of low significance in the absence of complementary data other than thermal analysis (163), infrared spectroscopy (163), or NMR spectroscopy (164). In this context, the Merck index lists the chemical formula of CBS as KgfNHJaBieOafOHMCeHsCbh in the 11th edition (165), but in the most recent edition provides a less precise name, tripotassium dicitrato bismuthate (166). 

Apart from the qualitative observations made previously about suitable solvents for study, the subject of solvates has two important bearings on the topics of thermochemistry which form the main body of this review. The first is that measured solubilities relate to the appropriate hydrate in equilibrium with the saturated solution, rather than to the anhydrous halide. Obviously, therefore, any estimate of enthalpy of solution from temperature dependence of solubility will refer to the appropriate solvate. The second area of relevance is to halide-solvent bonding strengths. These may be gauged to some extent from differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) solvates of "aprotic solvents such as pyridine, tetrahydrofuran, and acetonitrile will give clearer pictures here than solvates of "protic solvents such as water or alcohols. 

All coals were ground to <500 ym and acid-washed to remove HCl-soluble Iron (28). The resulting specimens were stored at 255 K under nitrogen. They were dried overnight under nitrogen at 378 K Immediately prior to thermal analysis or addition of pyridine. 

The long-term operation of a continuous reaction process with catalyst recovery requires a catalyst with very good thermal stability. Unfortunately the tetra(n-alkyl) ammonium iodides which have good solubility properties also have poor thermal stability due to breakdown by dealkylation. This was observed during operation of the continuous process and in thermal analysis. Thermogravimetric... 

Urszula Domahska has been professor. Faculty of Chemistry, Warsaw University of Technology since February 1995. She has been the Head of the Physical Chemistry Division since September 1991 and vice director of the Institute of Fundamental Chemistry (1988-1990). She had long-term scientific visits as visiting professor Laboratoire De Thermodynamique Ft D Analyse Chimique, University of Metz, France University of Turku, Finland Faculty of Science, Department of Chemistry, University of Natal, South Africa Department of Chemical Engineering, Louisiana State University, United States. Her interests have included such areas of physical chemistry as thermodynamics, especially thermodynamics of phase equilibria, VLE, LLE, SLE, high-pressure SLE, separation science, calorimetry, correlation and prediction of physical-chemical properties, and ionic liquids. She is a member of the Polish Chemical Society member of the Polish Association of Calorimetry and Thermal Analysis member of lUPAC Commission on Solubility member of International Association of Chemical Thermodynamics and scientific advisor at the Journal of Chemical Engineering Data. 

The acrylonitrile cellulose grafts were examined by differential thermal analysis, solvent extraction and solubility studies. They conclude from their data that the unextractable portion is present mainly in grafted form. 

Graft and block copolymers of cotton cellulose, in fiber, yam, and fabric forms, were prepared by free-radical initiated copolymerization reactions of vinyl monomers with cellulose. The properties of the fibrous cellulose-polyvinyl copolymers were evaluated by solubility, ESR, and infrared spectroscopy, light, electron, and scanning electron microscopy, fractional separation, thermal analysis, and physical properties, including textile properties. Generally, the textile properties of the fibrous copolymers were improved as compared with the properties of cotton products. 

Macroradicals obtained by the heterogeneous copolymerization of styrene and maleic anhydride in poor solvents such as benzene were used to initiate further polymerization of selected monomers. This technique was used to produce higher molecular weight alternating copolymers of styrene and maleic anhydride and block copolymers. Evidence for the block copolymers was based op molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. 

Quantitative PXRD and thermal analysis have been used to determine solid solubility of drugs in polymeric carrier [132-134], When phase separation occurs in solid dispersion, it results in formation of a drug-rich phase and a polymer-rich phase. The polymer-rich phase could retain, either by restricting molecular mobility or by interacting with drug, a certain portion of drug within its matrix. 

Bikiaris, D., G. Z. Papageorgiou, A. Stergiou, E. Pavlidou, E. Karavas, F. Kanaze, and M. Georgarakis. 2005. Physicochemical studies on solid dispersions of poorly water-soluble drugs. Evaluation of capabilities and limitations of thermal analysis techniqiT ffirmochnica Act 39 58-67. 

As part of the preformulation activities, investigations include physiochemical character, purity, solubility, stability, and optimal pH studies. In preparation for clinical studies, potential product formulations considering route of administration and solution stability are also studied. Unique to dosage form development studies for lyophilized products, thermal analysis of the drug substance and product formulations are also necessary. Data generated during this phase of product development is useful for future development activities, along with validation. 

Iwatsuki, M., T. Kyotani, and K. Matsubara. 1998. Fractional determination of elemental carbon and total soluble and insoluble organic compounds in airborne particulate matter by thermal analysis combined with extraction and heavy liquid separation. Anal. Sci. 14 321-326. 

Solvent-soluble organics Extraction and carbon detection differential thermal analysis... 

The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kUobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO2-rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with Pt02 to form cubic Pb2Pt207. Several corundum-type sesquioxides exhibit measurable solubility in PtOz. Two series of compounds are formed with metal monoxides M2PtOh (where M is Mg, Zn, Cd) and MPt306 (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 

Unlike divalent oxides, the solubility of alumina is low and hence some warm temperature treatment is required. In addition, rather than using lower solubility phosphate solutions such as ammonium and potassium phosphate solutions, phosphoric acid solution is directly used. Wagh et al. [ 17] employed a thermodynamic analysis to study the elfect of the temperature on the solubility of individual phases of alumina on the formation of its phosphate phases during heat treatment where solubility of hydrated aluminum oxide, viz., hydrargillite (A1203-3H20) is enhanced, and that contributes further to the formation of berlinite phase. They confirmed this by differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis on samples heated beyond 118°C. 

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