Filtration accelerated solvent extraction

Chapter 8 provides practical guidance on the use of widely used extraction and isolation techniques from the sample preparation perspective. The first two sections, solid-phase extraction and liquid-liquid extraction deal with liquid samples. The sections on supercritical fluid extraction and accelerated solvent extraction focus mainly on solid samples while the centrifugation and filtration sections handle suspensions. A successful sample preparation protocol accounts for specificity and homogeneity as well as recovery and final physical state of the targeted material. The ultimate aim is to produce a sample that is compatible with the desired analytical technique to assure generation of maximum information. 

Membrane filtration is a widely used but narrowly understood technique for sample preparation in chemical analysis. This section has the goal of providing some basic information to aid in the use of filtration tools with drug impurities. Many of the common sample preparation approaches described elsewhere in this chapter, such as liquid extraction, supercritical fluid extraction, and accelerated solvent extraction are effective at removing the dissolved analytes of interest from the matrix while leaving behind many poorly soluble or insoluble matrix components. In contrast, filtration is designed to remove these suspended particles from the extract prior to subsequent analytical steps. Unfiltered samples can destroy the performance of a downstream analytical technique such as HPLC or optical spectroscopy.68,69... 

Particulate matter, obtained from the filtration process, can be analyzed with the same analytical methods normally used for sediment samples. Solvents used in the filter extraction are generally the same as those previously described for liquid-liquid extraction (i.e., -hexane [152], toluene [31], and pentane/mefhylene chloride (2 1) [85]). However, water-miscible solvents can also be used such as acetone, ethyl acetate and methanol (n-heptane/acetone (1 1) [67], hexane/acetone (3 2) [10], dichloromethane/methanol (2 1) [46], and dichloromethane/methanol (2 1) [135]). The extraction process is carried out in a Soxhlet extractor or, more simply, in an ultrasonic bath— this improves the exchange process between the particle surface and the bulk of the organic solution. Pressurized liquid extractions (accelerate solvent extraction) can be used for a more efficient extraction, above all in terms of extraction times [10,67]. 

In microwave assisted extraction (MAE), microwave energy accelerates the partition, i.e. the mass transfer of an analyte from a sample matrix into a solvent, by directly heating the solution. The extraction is performed at an elevated temperature in a closed vessel. The major benefits are the shorter extraction time, reduced consumption of organic solvents and increased sample throughput. However, there is a need for an additional filtration step and, if the extract is dilute, further concentration, e.g. by evaporation or SEE, may be needed before analysis. 

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