Extraction, of solutes

Extraction of solutes from ionic liquids with compressed gases or... 

The most common method of isolation and sample cleanup involves contacting a filtered aqueous solution with an appropriate immiscible organic solvent in a. aboratory separatory funnel of appropriate size. Some specific examples are discussed later. With multicomponent samples a single solvent or solvent mixture is unlikely to extract all components equally causing discrimination. Ihis discrimination may be useful if the solvent discriminates against the extraction of solutes that are not of interest in the analysis. 

From infiltrating water that has extracted solute from the soil or free product in its path due to the extraction of solute directly from soil adsorbates... 

Extraction Apparatus.—Very often an organic substance is so much more soluble in water than in ether and other solvents that shaking with a solvent even when repeated is ineffective. In such cases an apparatus for continuous extraction of solutions is used it should not be wanting in any organic laboratory. The apparatus of Schacherl (Fig. 25), which can be constructed from simple laboratory materials, indicates the principle involved. Still more convenient is the apparatus shown in Fig. 26. It likewise can be constructed in all dimensions from easily obtainable materials. 

In multiple extraction of solute from aqueous to organic phase, if the volume of the organic solvent used each time remains constant and equal to the volume of aqueous phase, the weight unextracted after n such operations is ... 

Microwave-assisted extraction (MAE) it has attracted growing interest, as it allows rapid extraction of solutes from solid matrices by employing microwave energy as a source of heat [42], The portioning of the analytes from the sample matrix to the extractant depends upon the temperature and the nature of the extractant. 

Solvent extraction may be accompanied by a chemical reaction. The selectivity and the extraction factor can be greatly improved by carrying out the extraction with a solution of an extractant that chemically converts the solute to a form that is preferentially soluble in the extracting solvent. An additional advantage of this procedure is that the reverse extraction of solute (stripping) can often be carried out by changing the equilibrium constant of the reaction, e.g., by changing the pH or temperature. 

Table 1 gives a summary of calculated times for 50% extraction of solute (t 50%)- Simulations conditions are P = 20 MPa, T = 313 K and Re = 40 for the system DCB/small cylinders and downflow operation. From Table 1, it is seen that for a constant value of Kq, a decrease of De and K lead to a significant increase of 150% irrespective of the Biot number. On the other hand, the influence of Kq is found to be significant only in the higher range of Biot number (Bi = 250) where the external mass transfer gradient may become limiting (Kq is very small). 

Figure 3 compares values of 6 of supercritical fluids for p = p,jq (where only the chemical nature of the fluid is taken into consideration). From this figure it can be seen that CO2 is a slightly polar fluid, and that at first sight the extraction of solutes strongly linked to a matrix will be difficult. 

Fahmy, T.M., Pulaitis, M.E., Johnson, D.M., McNally, M.E.P., Modifier effects in the supercritical fluid extraction of solutes from clay, soil, and plant materials. Anal. Chem., 65 (10), 1462-1469,1993. Langenfeld, J.J., Hawthorne, S.B., Miller, D.J., Pawliszyn, J., Role of modifiers for analytical scale supercritical fluid extraction of environmental samples. Anal. Chem., 66(6), 909-916,1994. Hawthorne, S.B., Methodology for off-line supercritical fluid extraction. In Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation, Westwood S.A. (Ed.), Blackie Academic and Professional, 39-64, 1993. 

A prerequisite for extraction of solutes from one phase to the other is the intensive interface contact of solvent and feed, followed by gravitational separation of the two coexisting phases. In all industrial extraction equipment, one phase is dispersed as droplets in the continuous phase. Thus the density difference is used to facilitate phase separation. The mass transfer rate is defined as ... 

For soil classification purpose the conductivity of saturation extracts of soils is required. However, extraction of solution from a saturated paste is very difficult process. As an approximation, the conductivity of the water extracts from a 1 2.5 soikwater suspension is determined and the conductivity of the saturation extract is calculated as EC (saturation extract) = E.C (1 2.5 extract) x 250/saturation percentage. 

Consider the conntercunetlt extraction of solute A from solution in B using pare solvent C. The operation is performed in the columa shown in Pig. 7.3-1, which may be either continuous-contact (packed) or stagewjse. 

Solubility and selectivity in a supercritical fluid are strong functions of temperature and pressure. For nearly total extraction of solutes by supercritical... 

As mentioned before, carbon dioxide is highly soluble in [C4CjIm]PFg, although the ionic liquid does not dissolve in carbon dioxide [103]. These properties can facilitate the extraction of solutes from the IL without contamination of the non-io-... 

Extraction of Solutes from Ionic Liquids with Compressed Cases or Supercritical Fluids... 

For other applications, like the selection of solvents for the liquid-liquid extraction of solutes from mixtures, solubility and related measures are determined on the basis of the liquid-phase activity coefficients, 7y, for solute-solvent pairs. Usually, for screening purposes, it is sufficient to estimate the liquid-phase activity coefficient at infinite dilution, 7,", using group-contribution methods. 

When considering solvent S for extraction of solute A from species B, Pretel and coworkers (1994) use the UNIFAC group-contribution method to obtain estimates of four solvent properties ... 

The main soluble intermediates could be readsorbed and oxidized to form CO2 or extracted from the surface under configuration of continuous flow rate. The last situation represents a loss of energy due to an incomplete methanol oxidation. This is well elucidated in the experiments where the extraction of solution in front of the electrode results in lower current than in experiments without sample collection [9]. For supported platinum, Jusys et al. [10] observed that an increasing conversion to CO2 would be attained with increasing Pt load by the cost of faster consumption of formaldehyde facts that are attributed to an increased readsoption rate on electrodes with enlarged electrochemical surface area. 

Although TLC/mass spectrometry (MS) has been shown to be technically feasible and applicable to a variety of problems, TLC is generally coupled with spectrophotometric methods for quantitative analysis of enantiomers. Optical quantitation can be achieved by in situ densitometry by the measurement of UV/VIS absorption, fluorescence, or fluorescence quenching, or after extraction of solutes from the scraped layer. The evaluation of detection limits for separated enantiomers is essential because precise determination of trace levels of a d- or L-enantiomer in an excess of the other becomes more and more important. Detection limits as low as 0.1% of an enantiomer in the other were obtained. 

The extraction of solutes from solid samples, according to the BIC model, can be divided into three periods the constant extraction rate, falling extraction rate, and diffusion (Sovova, 1994). In the first period, the easily accessible solutes are extracted at a constant rate until the particles at the bed entrance lose all their accessible solutes. At this time, the diffusion extraction of the entrance of the bed begins, combined with convection extraction of the rest of the bed. This results in a continuation of the extraction for broken cells, beyond the bed entrance, and at the same time the extraction of cells begins at the bed entrance and the rate of extraction decreases. At the end of this stage, all of the broken cells are extracted and only the intact cells are left. Thus the extraction becomes diffusion controlled. According to this, the simplified mass balances of the fluid and solid phases are described by Equations 5.1 and 5.2, respectively ... 

The mechanism of the extraction of solutes from porous structures into a near-critical solvent is regarded (see for example O Toole et al [93]) as taking place in three stages ... 

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