Extractants optimum composition

Situations can be imagined, in which more than one solute has to be extracted from a sample. Such situations are, for instance, the extraction of an analyte simultaneously with an internal standard or a drug simultaneously with one or more major metabolites or co-drugs. Under these conditions, the aim of an extraction procedure is to extract all substances as quantitatively as possible. However, for each solute to be extracted the optimum composition may be located in another region of the factor space there may be no such combination of mixture variables, that guarantees optimum extraction for all substances. 

Similar to the criterion of the minimal partition coefficient, one can also use the criterion of the minimal selectivity. This criterion (a , ) is defined as follows an extraction liquid composition is optimal if there is no other composition that gives a higher value for the minimal selectivity (maximise In other words the optimum composition is that... 

Application of bis-(2-ethylhexyl) orthophosphate as a liquid ion exchanger in the complete or selective extraction of alkaloids from a buffered aqueous phase has been described. The behaviour of the salts of various alkaloids upon titration with base has been compared.Correlations have been made between the Rf of a number of alkaloids and the pH of an aqueous buffer solution which extracts half of the alkaloid from an aqueous solution. The stabilization of alkaloid solutions has been discussed. " Chromatographic separations of alkaloids by ion-exchange, adsorption, thin-layer, paper, and liquid chromatography have been reviewed. Reference lists have been compiled for methods and applications published in 1970—73 of chromatography and of electrophoresis of alkaloids on paper and thin layers. The optimum composition of Dragendorff s reagent for efficient alkaloid precipitation has been examined. ... 

A research project (carried out under the former BCR and coordinated by the CID-CSIC in Barcelona, Spain) also enabled development of a supercritical fluid extraction procedure which was successfully applied to the certification of TBT in the CRM 462 [99]. The effect of extraction variables, such as extraction time, temperature and extraction agent composition, in supercritical fluid extraction have been optimized by using a factorial-fractional experimental design. Under the optimum conditions (T = 60 °C, P = 35 MPa, 5.1 mol methanol in CO2, t = 30 minutes), the TBT extraction efficiency was 82% with a coefficient of variation of 9.2% (after determination by GC-FPD). 

If the feed, solvent, and extract compositions are specified, and the ratio of solvent to feed is gradually reduced, the number of ideal stages required increases. In economic terms, the effect of reducing the solvent-to-feed ratio is to reduce the operating cost, but the capital cost is increased because of the increased number of stages required. At the minimum solvent-to-feed ratio, the number of ideal stages approaches infinity and the specified separation is impossible at any lower solvent-to-feed ratio. In practice the economically optimum solvent-to-feed ratio is usually 1.5 to 2 times the minimum value. 

The mechanical piopeities of stmctuial foams and thek variation with polymer composition and density has been reviewed (103). The variation of stmctural foam mechanical properties with density as a function of polymer properties is extracted from stress—strain curves and, owkig to possible anisotropy of the foam, must be considered apparent data. These relations can provide valuable guidance toward arriving at an optimum stmctural foam, however. 

Ultrafiltration of heterogenous colloidal suspensions such as citrus juice is complex and many factors other than molecular weight contribute to fouling and permeation. For example, low MW aroma compounds were unevenly distributed in the permeate and retentate in UF in 500 kd MWCO system (10). The authors observed that the 500 kd MWCO UF removed all suspended solids, including pectin and PE. If PE is complexed to pectate in an inactive complex, then it is conceivable that release of PE from pectin with cations will enhance permeation in UF. At optimum salt concentration, less PE activation was observed at lower pH values than at higher pH (15). In juice systems, it is difficult to separate the effect of juice particulates on PE activity. Model studies with PE extracts allows UF in the absence of large or insoluble particulates and control of composition of the ultrafilter. In... 

In the right part of Figure 7.1, the maximal minimal partition coefficient is found in O,. Here, the composition where the ratio of the partition coefficients of compounds i and j reaches its optimum, Oo, is also the composition that gives a robust selectivity. Optima with respect to maximal partition coefficients of both compounds are obtained with different compositions. The response surfaces are not completely parallel. Little variation in the composition of the extraction liquid does influence... 

CB could be fractionated into 3 fractions on the continuous pilot-scale system without ethanol. Table 2 shows experimental conditions and yields of the fractions obtained. Trials were run at 24.1 MPa and 40 °C and the solvent-to-feed ratio (S/F) was 116-120. The S/F ratio was chosen based on our work with milk fat. The optimum S/F for fractionation of milk fat at the same temperature and pressure was 55-60 [4], Composition of CB is significantly different from that of milk fat. Twice the S/F ratio as that for milk fat was used. The solubility of CB in SC-C02 under the given extraction conditions was 0.58 wt%. As mentioned earlier, CB solubility is low in SC-C02 compared to other fats and oils, e.g. milk fat has an equilibrium solubility of 2.1 wt% at 24.1 MPa/40 °C. 

The composition of the SARP reject acid or extractor bottoms will vary depending on a lot of factors, but for most of the V(ork with less than optimum conditions in the absorption, extraction and acid treating steps, a fairly typical analysis is shown in Table 2, below. For orientation purposes an analysis of used alkylation acid is also shown. 

These results imply that since residual crude oil composition changes as it undergoes extraction by injected COj, the optimum COj mobility control agent may change during the course of the COj flood. 

The membrane composition should be such that the membrane should be stable and at the same time should have reasonable solute extraction capability. Studies by a number of researchers [10, 45, 58] reveal that the initial extraction rate increases wich increase in surfactant concentration. This is due to the fact chat addition of more surfactant lowers the surface tension and results in smaller droplet size of the W/O emulsion, which gives a larger mass transfer area and thus more efficient solute extraction. With low surfactant concentration, it was observed in certain cases that after large contact times, the external phase solute concentration shghtly increases. Lee and Chan [10] observed that a large amount of surfactant increases the viscosity of the membrane phase and lowers the diffusivity of the solute through the membrane thereby decreasing solute extraction rate. Hence the surfactant concentration cannot be increased indefinitely and there exists an optimum value beyond which if it is increased, the extraction rate may be adversely affected. Chaudhuri and Pyle [58] found that for extraction of lactic acid with Span 80 as surfactant, with 1-2% ot the surfactant concentration, the external phase lactic acid concentration increased after about 3-4 min contact time. Lee and Chan [10] found this optimum value to be 6%. 

PHB Under optimum conditions, in the accumulation phase during the fermentation process, the rate of the enzymatic degradation of this amorphous PHB is extremely fast, within a few hours. In contrast to this, extracted or processed, partially crystalline PHB is attacked relatively slowly over periods of weeks. The enzymatic decomposition, for example, of the PHB test specimen, leads to a slow surface erosion, while the volume body remains unchanged for some time, so the whole weight and the properties change slowly. The enzymatic degradation occurs at the surface of the PHB material and the rate of the surface erosion is strongly dependent on both the structure and the composition. 

A well-known extraction system is supercritical fluid extraction. It can be applied to matrices of different composition. This technique demonstrates the influence of matrix characteristics and common extraction variables on equilibrium analyte distribution.63 These factors assure, for supercritical fluid extrachon, the optimum conditions for efficient extraction of the matrix. 

This concept of optimum aromaticity and the role of sulfur compounds as inhibitors were further established by a study by Bum and Greig (British Petroleum) of the oxidation of solvent extracted base stocks.18 They chose samples from a North African (Sahara) and three Middle East (Iran, Abu Dhabi, and Kuwait) crudes. The aromatic + heterocyclic (A + II) and paraffin + naphthene (P + N) components were separated by alumina chromatography from each base stock (Table 5.9 includes their composition and sulfur contents) and recombined in several ratios and the resistance of the blends to oxidation measured by the oxygen uptake method. 

For the comparison of the performance of ASE with commonly used extraction methods such as SE and MAE, standard-spiked PUF and filter samples were processed separately. An overall comparison between the recoveries is shown in Fig. 3, in which the individual bars represent the average values obtained from triplicate measurements for each target compound. All extraction techniques used the HEX/ACE solvent composition and the optimized extraction time and temperature (for SE and MAE, the optimum conditions are from the literamre). The recoveries of SE even after 8 h extraction were significantly lower than those of MAE (20 min) and ASE (40 min 2 cycles x 20 min/cycle) for both PUF and filter samples, respectively. Although MAE and ASE-1 cycle achieved similar efficiencies, ASE-2 cycles gave the best recovery for all target compounds. Furthermore, good reproducibility was also obtained for ASE, which is most likely due to the automation of the whole extraction procedure. 

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