Solubility-limiting methods

FLAVOR MODIFICATION TECHNOLOGIES Solubility-Limiting Methods... 

Due to the small emission and absorption cross sections of Er +, a high Er density is needed to reach reasonable values of optical gain. Typically Er densities are between 0.1% and 1.0% (10 -10- Er/cm- ). These values are far beyond the equilibrium solubility limits of Er in silicon. Therefore, nonequilibrium methods have to be used, such as ion implantation. Er implantation in crystalline silicon leads to amorphization, and additional annealing (600°C) is required to... 

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. 

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... 

Limited method development (Hildebrand solubility parameters for solvent choice)... 

For systems that are only partially miscible in the liquid state, the activity coefficient in the homogeneous region can be calculated from experimental values of the mutual solubility limits. The methods used are described by Reid et al. (1987), Treybal (1963), Brian (1965) and Null (1970). Treybal (1963) has shown that the Van-Laar equation should be used for predicting activity coefficients from mutual solubility limits. 

For this method, either a weighed amount of the solute (or a definite amount of the solvent) is placed in a suitable vessel. While agitating the system at constant temperature, known amounts of the solvent (or the solute) are added gradually until the solubility limit is reached. Appropriate checks must be carried out to ensure that the system is very close to equilibrium when the content or temperature of the system is recorded. In this method of temperature variation, attention is usually focused on the last small crystal. The equilibrium temperature is taken as the mean of the two temperatures at which the crystal either slowly grows or slowly dissolves. This procedure may also be carried out at the microscale by examining a small volume of the system under a hot-stage microscope. 

This method is best solved graphically by plotting the maximum concentration measured at the center of the plume on different dates, then extrapolating to determine the date on which the concentrations of the contaminant in question approaches its solubility limit. The solubility limit, corrected for the temperature of the aquifer, for a particular contaminant can be obtained from the literature. 

It is assumed that the contaminant enters the water table or aquifer at a concentration near its solubility limit, although there is no practical means to verify this. This method is more favorable when the release occurred as a single, short-term episode. A long-term release from a continuing source would result in a date that more closely represents the last date upon which the contaminant entered the aquifer at or near its solubility limit. Should the contaminant enter the aquifer below its solubility limit, then a date earlier than the actual event would result. Conversely, should the contaminant enter the aquifer as NAPL for a period of time, a date in which all the NAPL dissolved in groundwater would result. If NAPL was present when measurements were obtained, then the zone of highest concentration would... 

EPA Method 9071A Sludge Used to recover low levels of oil and grease from sludge. Used when relatively polar, heavy petroleum fractions are present, or when the levels of nonvolatile greases challenge the solubility limit of the solvent. Not recommended for measurement of low-boiling fractions. 

A phase diagram is often considered as something which can only be measured directly. For example, if the solubility limit of a phase needs to be known, some physical method such as microscopy would be used to observe the formation of the second phase. However, it can also be argued that if the thermodynamic properties of a system could be properly measured this would also define the solubility limit of the phase. The previous sections have discussed in detail unary, single-phase systems and the quantities which are inherent in that sjrstem, such as enthalpy, activity, entropy, etc. This section will deal with what happens when there are various equilibria between different phases and includes a preliminary description of phase-diagram calculations. 

The effectiveness of magnesium enolates as nucleophilic agents limits the interest of the reaction. With less substituted substrates (R = H), the aldol reaction is faster than the sily-lation. Moreover, due to solubility limitations, the authors are unable to determine whether the high thermodynamic kinetic ratio of silylenol ethers obtained accurately represents the magnesium enolate composition. Nonetheless, this method is an excellent procedure to selectively prepare the thermodynamic silylenol ether from an unsymmetrical ketone. ... 

In order to overcome the solubility limitation typical of lignin fractions, chemical modifications have been envisaged. Obviously only those methods giving nearly quantitative recovery are adequate for the purpose of measuring Mn- Table V shows results related to the acetylation technique where only a slight increase in M is observed as expected. 

Lyophilic sols are true solutions of large molecules in a solvent, Solutions of starch, proteins, or polyvinyl alcohol in water are representative of numerous examples. Properties of these solutions at equilibrium (for example, density and viscosity) are regular functions of concentration and temperature, independent of the method of preparation. The solvent-macromolecule compound system may consist uf more than one phase, each phase in general containing both components. Thus, if a solid polymer is added to a solvent in an amount exceeding the solubility limit, the system will consist of a liquid phase (solvent with dissolved polymer) and a solid phase (polymer swollen with solvent, i.e., a polymer with dissolved solvent). 

---