Factors affecting extraction efficiencies

Efficient extraction of manganese is also obtained with sodium diethyldithio-carbamate/n-butyl acetate in a pH range from 4-8. Various factors affecting extraction efficiency were recently examined in detail66). 

For practical reasons, classical procedures are continuously upgraded to get improvements in terms of reliability and performance. Such an approach relates, for example, to the conventional Soxhlet extraction assisted by focused microwaves (FMSE). The main factors affecting extraction efficiency are microwave power, irradiation time, volume of the extractant, and number of cycles. The result, in terms of extracted mass and repeatability is similar to the classical method. In addition, there is a significant reduction in the total time taken for the process and far less amount of extractant is consumed. Organo-chlorine pesticides (OCPs) and related residues have been successfully isolated from sunflower seeds by means of FMSE. Comparison with the ISO 659-1988... 

Temperature is a very important factor that affects extraction efficiency, regardless of the applied technique. During MAE carried out in a closed vessel the... 

Over the projected hfe of a commercial-scale oil sands operation, such as Syncrude, the volumes of process-affected waters will be large. The quality and quantity of this water may affect water usage in the plant, as well as both onsite and offsite reclamation approaches [136]. As can be seen in Figure 31(a), much of the plant water requirements are drawn from the water released from the various sinks. To ensure optimized use of this water, factors that would adversely affect extraction efficiency or plant performance (scaling, corrosion) must be minimized. 

Factors that affect the phase volumes and equilibrium constants, such as temperature, pressure, aqueous phase pH, additives, and matrix interferences, may strongly affect extraction efficiency and performance and will need to be controlled carefully. The practical consequences of salt and pH effects are shown in Figure 11.18. 

One limitation of carbon dioxide as an extractant is its polarity. In its supercritical state and at low densities, CO2 has a polarity close to that of hexane. Even at extremely high pressures the solubility parameter may not approach that which is required to solubilize and extract polar analytes. This limitation can be overcome by the use of another extraction fluid, which is more polar, or by adding a polar modifier to the CO2. The most commonly used modifier with CO2 has been methanol. Increased solubilities and recoveries of polar analytes have been reported when a polar modifier is added to a less polar supercritical fluid (66-68). The ability of the supercritical fluid to dissolve a particular analyte is not the only factor, which affects extraction efficiency. The degree to which the analyte partitions into the supercritical fluid fi om the solid-sample matrix depends greatly on the sorptive and active sites on the solid matrix and the polarity of the solute (64,69). The addition of a polar modifier or entrainer, such as methanol, to a supercritical fluid such as CO2, not only increases the solubility of polar analytes in the supercritical fluid, but also may help block sorptive sites on the surface of the sample matrix. 

There are several factors that affect extraction efficiency and in general the efficiency depends on the mixing/settling and coalescence characteristics of the system. Important factors include ... 

Harrison et al. [33] studied the factors governing the extraction and gas chromatographic analysis of PAHs in water. Factors such as initial concentration, presence of suspended solids and prolonged storage of the samples affected considerably extraction efficiencies. It is recommended that water samples should be collected directly into the extraction vessel and that analysis should be carried out as soon as possible after extraction. 

In some cases, the flow-rate is the single factor most strongly influencing the extraction efficiency the higher it is, the greater the amount of analyte that is extracted over a given interval [38]. In other cases such as the extraction of fluoranthene from soil, the flow-rate scarcely affects the results above a 0.3 ml/min level [41]. The optimum conditions for a particular extraction cannot be established on the basis of the number of times the extraction cell is vented because the extraction of most analytes is kinetically limited. Occasionally (e.g. in the extraction of cocaine from coca leaves), the process is governed primarily by the solubility of the analyte rather than by its desorption kinetics (see Fig. 7.10) [22]. 

Shu, Y. Y., Lai, T. L., Lin, H., Yang, T. C., and Chang, C., Study of factors affecting on the extraction efficiency of polycyclic aromatic hydrocarbons from soils using open-vessel focused microwave-assisted extraction, Chemosphere, 52, 1667-1676, 2003. 

Bioavailability, that is, the availability of the bioactive compounds at the cellular level to an organism when consumed, is one of the major factors which govern the effectiveness of different bioactive compounds. Bioavailability is affected by various factors which have been discussed in different reviews [8, 9]. It has been observed that sometimes either the pure form of a polyphenol is more helpful or combinations of some particular polyphenols are more effective. Hence, extraction of the bioactive compounds with efficient processes, proper separation with least losses, and encapsulation with appropriate methods are required. For all the studies related to bioactive compounds such as polyphenols, including characterization, quantification, or biomedical in vivo or in vitro studies, extraction is the fundamental method which can be divided into the various steps, mainly preparation, extraction, separation, and purification [10]. This chapter concentrates on the phenols and properties of phenol which affect the extraction efficiency. Other factors affecting the extraction efficiency have also been discussed along with the different methods of extraction. Different methods of separatirni applied for the polyphenols have also been discussed. 

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