Solubility static method

Gong and Cao described A. annua SEE of artemisinin (1) in SCCO2 determined by static method at three temperatures (313, 323 and 333 K) and pressures varying between 11 and 31 MPa. The solubility data ranged from 0.498 x 10 to 2.915 x 10 mol/mol under these conditions. Two density-based models (Chrastil s and Mendez-Sanfiago-Teja s) were selected to correlate the experimental data and the average absolute relative deviation was 8.32% and 8.33%, respectively. The correlation results were in agreement with experimental data. 

The solubility enhancement method is the most straightforward static technique in which the apparent solubility (S w) of a HOC is measured in the presence of increasing amounts of DOM (Chiou et al., 1986, 1987 Chin et al., 1997 Uhle et al., 1999). Briefly, the analyte is added in excess (10-100 times the reported aqueous solubility) to glass reactors by plating the solute out from a stock solution. Buffered DOM solutions at various concentrations are added to each tube along with a control reactor containing... 

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. 

SOLUBILITY MEASUREMENTS OF p-CAROTENE WITH A STATIC METHOD... 

Static Methods for Measuring Solubilities in Supercritical Fluids 91... 

STATIC METHODS FOR MEASURING SOLUBILITIES IN SUPERCRITICAL FLUIDS... 

The flow method ts the simplest and the most straightforward. In the flow method, the solvent fluid is supplied to a compressor by a pressure cylinder. At the desired pressure, the fluid passes into the thermostatted extractor cell that contains the solute present in appropriate matrix (e.g., multiple layer of glass wool). The fluid dissolves the solute in the extractor and, on expansion through a heated metering valve, precipitates solute into a series of collection vessels to be measured gravimetrically. The volume of the decompressed fluid is totaled by a wet or dry gas test meter. Static or equilibrium solubility measurement methods are used to eliminate the need to sample the supercritical fluid solution. A high-pressure flow cell is placed in the flow circuit to monitor the dissolution process by spectrophotometry. 

Figure IL Conditions for solubility measurements with the static method.

Figure 13. Solubilities ofCu(II)-dialkyldithiocabamates with different residual substituents measured with the static method at given conditions...

Tutna, D. Schneider G.M. High Pressure Investigations on the Solubility of Disperse Dyes in Near- and Supercritical Fluids Measurements up to 100 Mpa by a static Method" The 4 International Symposium on Supercritical Fluids 1997. 

Current official GC methods are described in USP XXIII under chapter 467 Organic volatile impurities . Four methods (I, IV, V, VI) are mentioned. Methods I, V and VI are based on direct injection. They are suitable for water-soluble drugs and V for water insoluble drugs. Method IV describes the static headspace technique and is used for water soluble drugs. Method VI is very general and refers to the individual monograph which describes the chromatographic conditions (injection, column, conditions) which should be used. The main characteristics of these four methods are summarized in Table 16.2.2. 

In some cases, the concentrations can be determined directly from UV/VIS/ NIR-spectroscopic measurements using Lambert-Beer s law (best in integrated form). A systematic study of the solubilities of some synthetic and natural dyestuffs in supercritical CO2 has been performed in our laboratory using a flow technique (up to 20 MPa see Figs. 27 and 28) [40-43,78-80] and a static method (up to 200 MPa see Figs. 17 and 18) [42,44-47,76,77], respectively. 

As shown in Figs. 17 and 18, some results on l,4-bis-(octylamino)-9,10-anthra-quinone (AQ08) obtained from the static method are plotted. Whereas the c p) isotherms in Fig. 17 intersect resulting in a complex temperature dependence, no intersection points are found for the c p) isotherms (Fig. 18). This makes clear that the dominant parameter for solubility is density, and that the unusual temperature dependence of the c p) isotherms mentioned above derives from the pVT behavior of CO2. For additional data and a detailed discussion see [40-42,45-47,76-80]. 

Tuma, D. and Schneider, G.M. (1998) High-pressure solubility of disperse dyes in near- and supercritical carbon dioxide measurements up to 100 MPa by a static method, J. Supercrit. Fluids 13, 37-42. 

D. Tuma and G. M. Schneider, Dyestuff solubilities in various near- and supercritical fluids up to 180 MPa, measured by a static method... 

The behavior of the solubility curves in the same temperature region but at pressures above the critical was determined by Petit and Weil at Grenoble. Their results, obtained by the circulation method, show the t3rpical horizontal section above the 27 K temperature (see Fig. 4). This peculiar behavior was also noticed by us while making some isobaric measurements on the solid-gas equilibrium above the critical temperature of hydrogen when the flow method was used. From an inspection of Fig. 2, it follows that there is a possibility of the retrograde increase of the concentration of the fluid in the supercritical region. Such an effect, however, cannot easily be detected by adynamic method as applied to our measurements on liquid-solid equilibrium. Consequently, we used the static method in our determinations. 

The predictions of all these expressions were verified by Daynes (3). The intercepts L were, for membranes about 1 mm. thick, suitably large for evaluating D, as Fig. 144(33) indicates. Most early measurements of solubility employed the static method (1), Wroblewski(29) found that Henry s law was obeyed Q = kp. The temperature dependence of the solu-... 

Static methods. In which the system of interest is enclosed in a magnetically stirred variable volume cell [64, 76] which in some cases contains a window. The temperature and pressure within the cell are accurately metered. The cell volume may be changed either using a mercury piston or a mechanical piston and samples of the fluid phases present may be obtained, if required, under conditions of constant temperature and pressure by suitably reducing the cell volume. In the windowed cell version [76] sampling is unnecessary for binary systems since the cell may be charged with known amounts of the two components and conditions adjusted to obtain trace presence only of one of the phases. In this way the dew- and bubble-point curves for binary systems may be established and similarly the solubilities of solids in compressed fluids may be determined. 

With semicrystalline polymers having moderate to high crystallinity, Tg may be poorly resolved. Other static methods used to measure Tg are the following refractive index gas difiusion/solubility thermal conductivity chain mobility [nuclear magnetic resonance (NMR)] specific volume (dilatometry). Experimentally observed Tg is a function of several variables including molecular weight, plasticizer content, test rate/fi equency, sample size, copolymers/blends, cross-linking, crystallinity, and tacticity. 

Surface tension methods measure either static or dynamic surface tension. Static methods measure surface tension at equilibrium, if sufficient time is allowed for the measurement, and characterize the system. Dynamic surface tension methods provide information on adsorption kinetics of surfactants at the air-liquid interface or at a liquid-liquid interface. Dynamic surface tension can be measured in a timescale ranging from a few milliseconds to several minutes [315]. However, a demarkation line between static and dynamic methods is not very sharp because surfactant adsorption kinetics can also affect the results obtained by static methods. It has been argued [316] that in many industrial processes, sufficient time is not available for the surfactant molecules to attain equilibrium. In such situations, dynamic surface tension, dependent on the rate of interface formation, is more meaningful than the equilibrium surface tension. For example, peaked alcohol ethoxylates, because they are more water soluble, do not lower surface tension under static conditions as much as the conventional alcohol ethoxylates. Under dynamic conditions, however, peaked ethoxylates are equally or more effective than conventional ethoxylates in lowering surface tension [317]. 

Supercritical fluid extraction can be performed in a static system with the attainment of a steady-state equilibrium or in a continuous leaching mode (dynamic mode) for which equilibrium is unlikely to be obtained (257,260). In most instances the dynamic approach has been preferred, although the selection of the method probably depends just as much on the properties of the matrix as those of the analyte. The potential for saturation of a component with limited solubility in a static solvent pool may hinder complete recovery of the analyte. In a dynamic system, the analyte is continuously exposed to a fresh stream of solvent, increasing the rate of extraction from the matrix. In a static systea... 

SFE can be carried out in three different ways. In a static extraction (no flow-rate), the extraction vessel is pressurised to the desired pressure with the extracting fluid and then simply left for a certain length of time. The main benefit of this method is that the fluid has time to penetrate the matrix. It is most applicable when the analyte has a high affinity for the solvent and a low affinity for the matrix and also when the solubility limit of the analyte in the fluid is much higher than the actual level reached during the extraction [89]. This method was popular in early SFE experiments but has declined in favour of dynamic SFE. Here, fresh SCF is continuously passed over the sample, extracting soluble compounds and depositing them in a suitable solvent or on a solid trap. The dynamic mode is particularly useful when the concentration of the solute... 

The ability of SFE-FTIR to perform a variety of extraction methods is a definite advantage, especially for the study of complex mixtures containing analytes of varying solubility. For analytes which are readily solubilised in C02, direct dynamic and direct static-dynamic SFE-FTIR methods are quite successful. Elimination of the trapping process reduces both analysis time and potential analyte loss arising from... 

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