Solubility isothermal methods

To determine the composition of bimetallic alkoxides formed via complex formation in solution and in the solid phase and to estimate their stability, we have applied physicochemical analysis — the investigation of the solubility isotherms in the systems M(OR)m- M (OR)n - L (solvent alcohol, ether, hydrocarbon, etc.). This method, common for the studies ofthe interaction of inorganic salts in water solutions, turned out to be rather fruitful in the chemistry of alkoxides. It permitted the study of the interaction ofthe components... 

In this paper solubility measurements of synthetic and natural dyestuffs are presented using VIS-spectroscopy. The investigations concentrate on two different methods. I. P-carotene was measured as a function of temperature and pressure in near- and supercritical C02 (289 to 309 K, 10 to 160 MPa) and CC1F3 (297 to 326 K, 12 to 180 MPa), respectively, using a static method. II. Additionally, the solubilities of l,4-bis-(n-alkylamino)-9,10-anthraquinones (with n-alkyl = butyl, octyl) were determined with a dynamic method in temperature and pressure ranges from 310 to 340 K and 8 to 20 MPa, respectively this method permits a continuous purification from better soluble impurities as well as the measurement of solubilities at the same time. For both anthraquinone dyestuffs intersection points of the solubility isotherms were found in the plot of concentration versus pressure. This behavior can be explained by a density effect. 

In this chapter we describe the methods used to calculate solubility isotherms as well as the entire phase diagram for binary and ternary solute-SCF mixtures. The objective of the first part of the chapter is to discuss the relevant physical properties of the solute and solvent pair that are needed to describe the intermolecular forces in operation between molecules in a mixture that ultimately fix solubility levels. A brief description is provided on the application of solubility parameters to supercritical fluids. 

In the present work, we review reliable methods to evaluate solubility isotherms in polymeric phases, and examine the conditions needed for predictive calculations. The EoS approach will be used to calculate the chemical potential and the sorption isotherms of low molecular weight species in polymeric mixtures. Both the cases of equilibrium (e.g rubbery) and non-equilibrium (e.g. glassy) states will be treated, showing how the results of classical thermodynamics can be extended to the case of non-equilibrium states. 

The so-called synthesis methods of solubility determination involve the preparation of a solvent-solute mixture of known composition, initially containing excess solute. The complete dissolution of the sohd phase is then observed, either when the mixture is subjected to slow controlled heating (the polythermal methods) or at constant temperature when small quantities of fresh solvent are sequentiahy added over a period of time (the isothermal methods). The disappearance of the sohd phase can be observed visually or monitored by recording some appropriate physical or physicochemical property of the system. 

Mixed matrix membranes based on fluorinated high free volume matrices loaded with fumed silica nanoparticles show attractive features, especially if compared to unloaded polymeric membranes. The addition of filler changes the FFV of the glassy polymeric matrix, thus positively affecting both solubility and diffnsivity. A simple procedure has been proposed to calculate the relevant properties of the MMM, which is based on limited experimental data represented by the solubility isotherm of a test penetrant and few values of diffusion coefficients. The nnexpected behaviour shown by the MMM obtained by using nano-filler loadings can be properly described by the method developed. The... 

A method of determination of the equilibrium constant of 1 based on measurements of solubilities has been divesed. So far equilibria involving Co(II), Ni(II), and Zn(ll) were investigated, chlorobenzene being used as an inert solvent. The determined solubility isotherms for chlorobenzene-pyridine mixtures are shown in Fig. 1, the compositions of solid phases in equilibrium being indicated. It is seen that solid complexes are very slightly soluble in pure chlorobenzene but their solubility increases more or less rapidly on increasing pyridine concentration. This effect is a result of the formation of... 

The isothermal method was used. Equilibrium was approached from both supersaturation and undersaturation. Samples of saturated solution were weighed, evaporated to dryness and heated strongly to form the pyrophosphate. The solubility was calculated from the weight of the pyrophosphate formed. 

The isothermal method was used. The solubility was determined by evaporating the saturated solutions and drying to constant weight. Cooling curves were determined for some of the mixtures. 

The reliability of the solubility data for cesium dihydrogenphosphate depends on the analytical method that was used. This matter was discussed by Bykova, et al. (3) and they were careful in their experimental work. Their data agree fairly well with those obtained by extrapolation of solubility isotherms measured by others (4). Therefore, the data of Bykova, et al, (3) as well as their equation for the temperature dependence of the solubility of cesium dihydrogenphosphate are recommended values. The solubility data published by others (5, 6) are rejectee because of analytical uncertainties. The only information that can be considered to be proved Is the occurrence of solid solutions in the CSH2PO4-NH4H2PO4-H2O and CSH2PO4-KH2PO4-H2O systems at 298 K,... 

The ternary solubility phase diagram of (S) - and (R) - propranolol hydrochloride in a mixed solvent of methanol and acetone was measured by isothermal method [25]. For isothermal method, enough amount of powder, namely lOfttO.lmg, was dissolved in the solvent of methanol in a test tube. Saturated solution samples were carefully withdrawn and filtered, and the concentration of which were analyzed by the HPLC system with employment of above-mentioned self-packed column. 

Isobaric-isothermal methods are often also called dynamic methods. One or more fluid streams are pumped continuoirsly into a thermostated equilibriirm cell. The pressure is kept constant during the experiment by controlling an effluent stream, irsually of the vapor phase. One can distinguish between continuorrs-flow methods and semi-flow methods. In continuous-flow methods, both phases flow throrrgh the eqrrihbrirrm cell. They can be used only for systems where the time needed to attain phase equilibrium is sufficiently short. Therefore, such equipment is usually not applied to polymer solutions. In semi-flow methods, only one phase is flowing while the other stays in the equilibrium phase. They are sometimes called gas-saturation methods or pure-gas circulation methods and can be used to measure gas solubilities in liquids and melts or solubilities of liquid or solid substances in supercritical fluids. 

The solubility isotherm at 25°C was established and the solid phase compositions were determined by Schreinemakers method. The system is eutonic. The eutonic point is at 8.23 wt% Nd2(Se04)3 and 37.16 wt% Yb2(Se04)3. Solid solutions based on Nd2(Se04)3 5H20 are observed for up to 70.09 mol% Yb2(Se04)3 beyond that mixed crystals based on... 

The same system has been studied previously by Boguslavsky et al. [29], who also used the drop weight method. While qualitatively the same behavior was observed over the broad concentration range up to the solubility limit, the data were fitted to a Frumkin isotherm, i.e., the ions were supposed to be specifically adsorbed as the interfacial ion pair [29]. The equation of the Frumkin-type isotherm was derived by Krylov et al. [31], on assuming that the electrolyte concentration in each phase is high, so that the potential difference across the diffuse double layer can be neglected. 

A range of different methods measures the solubility of hydrogen in metals and alloys. Manometric methods [98] and gas volumetric methods [99] have been used to determine pressure-composition isotherms at selected temperatures for a range of alloys [100-103],... 

A radioactive tracer method was developed to quantitatively measure the adsorption of high molecular wt compds on the surfaces of powdered expls. Expts were conducted by allowing a pre-weighed amt of powdered expl to equilibrate with a fixed volume of radioactive adsorbate in an appropriate solvent. The expl must be either insoluble or of very low solubility in the solvent used. At equilibrium, an aliquot of supernatant soln is removed and its radioactivity is measured. The loss in radioactivity is a measure of the amt of adsorbate taken up by the expl. By varying the concn of adsorbate in the soln, an adsorption isotherm can be constructed relating amount adsorbed with solution concn... 

The NMR method we have developed gives a direct, in situ determination of the solubility and also allows us to obtain phase data on the system. In this study we have measured the solubilities of solid naphthalene in supercritical carbon dioxide along three isotherms (50.0, 55.0, and 58.5°C) near the UCEP temperature over a pressure range of 120-500 bar. We have also determined the pressure-temperature trace of the S-L-G phase line that terminates with the UCEP for the binary mixture. Finally, we have performed an analysis of our data using a quantitative theory of solubility in supercritical fluids to help establish the location of the UCEP. 

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