Advantages And Disadvantages Of Solid Phase Extraction (SPE)
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Solid phase extraction (SPE)
Solvent extraction has been largely replaced by solid phase extraction (SPE). SPE provides several advantages over LLE including higher recoveries, elimination of emulsion, less organic solvent usage, easier operation and possibility of automation, improved selectivity and reproducibility and shorter sample preparation time. This method is often the preferred way to extract and preconcentrate organics at low or very low levels from aqueous systems. SPE is not only widely used in water analysis, it is also extensively used for extraction of material from biological systems for instance, drugs of abuse in urine, or blood analysis. The most widely used SPE systems apply a small bed of a specific adsorbent material…show more content… Selective filter is also known as membrane, either to only limit the diffusion between two solutions or acts as an active membrane in which the selectivity of sample transferred can be determined by chemical structure of the membrane.  The most crucial membrane extraction technique is supported liquid membrane (SLM) extracton, which is based on a three-phase system (aqueous/or-ganic/aqueous) in which organic phase is immobilized in a hydrophobic porous polymer membrane, located between two aqueous liquids which are the donor and accepter in a flow system. All of the analytes should pass through the organic membrane liquid by a diffusion process as uncharged species. Microporous membrane LLE is the second membrane-extraction technique based on two-phase system (organic and aqueous).…show more content… Mostly suitable for high or moderate polarity analytes such as sulfonamides and they are useful when size or charge can be used to achieve selection. 
Ultrasonic extraction (USE)
This is technique is mostly used for extraction of analytes of interest from solid samples. This method uses mechanical energy in the form of shearing action, which is created by a low-frequency sound wave. The sample is first dissolved in the solvent, and it is immersed in an ultrasonic bath and provided few minutes of ultrasonic radiation. Extracted analytes are removed from the matrix by vacuum filtration or centrifugation. Two to three times the process is repeated to have higher extraction efficiency and the extracts are combined for analysis.  USE has the advantage of extraction times slower than classical liquid extraction techniques. The main disadvantage of USE is poor reproducibility due to lacking of distribution uniformity of ultrasound energy. Since both specificity and sample enrichment abilities are limited, additional clean-up and/or concentration steps are normally needed for identification of trace analysis.