Accelerated solvent extraction matrices

The first step for the determination of PAHs is removal from the matrix by solvent extraction, which preferably is performed with boiling toluene or benzene (hot solvent extraction by refluxing see Jacob and Grimmer 1994), although other solvents (e.g. tol-uene/acetone, acetone, and dichloromethane) and other extraction procedures (ultrasonic treatment, Soxhlet extraction, and accelerated solvent extraction) can also be applied. 

MAE simply involves placing the sample with the solvent in specialized containers and heating the solvent using microwave energy. MAE is also sometimes called MASE, which can stand for microwave-assisted solvent extraction or microwave-accelerated solvent extraction. In any event, the extraction process is more rapid than Soxhlet extractions, can be run in batches, and reduces solvent consumption. As in the case of sonication, MAE may overcome retention of the analyte by the matrix, but analyte degradation can be a problem at higher temperatures in certain applications. 

Accelerated solvent extraction is a new technique for the extraction of a range of organic pollutants from soils and related material. The technique is based on the use of a solvent or combination of solvents to extract organic pollutants at elevated pressure and temperature from a solid matrix. The range of organic pollutants for which the technique is proposed includes semivolatile compounds, organochlorine pesticides, organophosphorus pesticides, chlorinated herbicides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons [53-56],... 

Another method (EPA 3545, accelerated solvent extraction) has been validated using a variety of soil matrixes, ranging from sand to clay. In the method, conventional solvents such as methylene chloride (or a hexane-acetone mixture) are heated [100°C, (212°E)] and pressurized (2000 psi), then passed through the soil sample (this technique is also suitable for application to petroleum sludge and petroleum sediment). The method has the advantage of requiring smaller solvent volumes than is required by traditional solvent extraction techniques. 

Wennrich et al. [167] investigated the capabilities of coupling accelerated solvent extraction with water as the extraction solvent and solid-phase microextraction to determine chlorophenols in polluted soils. Subcritical water extraction was performed using a commercially available accelerated solvent extractor. This system solves the problem of the analytes partitioning back to the soil matrix, which can occur in straightforward subcritical water extraction because in the Wennrich et al. method [167] the aqueous phase and the soil are separated under the extraction conditions. 

For example, in the analysis of chlorophenol in soil by accelerated solvent extraction followed by GC-MS, deuterated benzene may be used as the matrix spike. The deuterated compound will not be present in the original sample and can easily be identified by GC-MS. At the same time, it has chemical and physical properties that closely match those of the analyte of interest. 

Accelerated solvent extraction (ASE) is also known as pressurized fluid extraction (PFE) or pressurized liquid extraction (PLE). It uses conventional solvents at elevated temperatures (100 to 180°C) and pressures (1500 to 2000 psi) to enhance the extraction of organic analytes from solids. ASE was introduced by Dionex Corp. (Sunnyvale, CA) in 1995. It evolved as a consequence of many years of research on SFE [45], SFE is matrix dependent and often requires the addition of organic modifiers. ASE was developed to overcome these limitations. It was expected that conventional solvents would be less efficient than supercritical fluids, which have higher diffusion coefficients and lower viscosity. However, the results turned out to be quite the opposite. In many cases, extraction was faster and more complete with organic solvents at elevated temperature and pressure than with SFE. Extensive research has been done on the extraction of a variety of samples with ASE. ASE was approved by EPA as a standard method in 1996. 

Pressurized solvent extraction (PSE), also called pressurized fluid extraction (PEE), accelerated solvent extraction (ASE ), pressurized liquid extraction (PEE), or enhanced solvent extraction (ESE), is a solid-liquid extraction that has been developed as an alternative to conventional extractions such as Soxhlet, maceration, percolation, or reflux. It uses organic solvents at high pressure and temperature to increase the efficiency of the extraction process. Increased temperature decreases the viscosity of the liquid solvent, enhances its diffusivity, and accelerates the extraction kinetics. High pressure keeps the solvent in its liquid state and thus facilitates its penetration into the matrix, resulting in increase extraction speed [30]. 

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... 

First of all, it is important to identify what the acronyms represent. The following have been used aMAE, atmospheric microwave-assisted extraction SFE, supercritical fluid extraction pMAE, pressurized microwave-assisted extraction PFE, pressurized fluid extraction ASE, accelerated solvent extraction MSPD, matrix solid-phase dispersion. 

Accelerated solvent extraction is a closed system of extraction which utilises higher temperature and pressure. Closed systems are designed to minimise the loss of volatiles, improve the efficiency and increase the throughput. The elevated temperature improves analyte solubility. For example, anthracene, a PAH, is 15 times more soluble in methylene chloride at 150°C than at 50°C. High temperature also helps to overcome sample extraction matrix effects and gives faster desorption kinetics. The lower solvent viscosity allows diffusion of the solvent into the matrix to occur more quickly than other extraction techniques. Increased pressure also elevates the boiling point of the solvent. 

Accelerated solvent extraction is a technique for the efficient extraction of analytes from a solid sample matrix into a solvent. The sample and solvent are placed in a closed vessel and heated to 50 to 200°C. The high pressure allows heating above the boiling point, and the high temperature accelerates the dissolution of analytes in the solvent. Both time of extraction and the volume of solvent needed are greatly reduced over atmospheric extraction. 

The procedure to be used to extract carbamate pesticides from environmental samples depends on their polarity and on the type of sample matrix involved. Various choices exist for the extraction of pesticides ranging from conventional procedures (e.g., Soxhlet extraction, liquid-liquid extraction (LLE), evaporation, steam distillation) to new methodologies including solid-phase extraction (SPE), solid-phase microextraction (SPME), supercritical fluid extraction (SEE), matrix solid-phase dispersion (MSPD), accelerated solvent extraction (ASE) and microwave-assisted extraction. " ... 

Current trends have been to accelerate the extraction of pesticides from the sample matrix by accelerated solvent extraction (ASE) or pressurized solvent extraction (PSE), microwave-assisted solvent extraction (MASE), and super critical fluid extraction (SEE). 

Pressurized liquid extraction (PEE) has received numerous names, such as accelerated solvent extraction (ASE), pressurized fluid extraction (PEE), pressurized hot-solvent extraction (PHSE), subcritical solvent extraction (SSE) and hot-water (H2O) extraction (HWE). PEE is carried out at temperatures above the boiling point of the solvent and uses high pressure to maintain the solvent in the liquid phase and achieve fast and efficient extraction of analytes from the solid matrix. HWE is being increasingly used in residue analysis, due to low cost, low toxicity, and ease of disposal. At ambient temperature and pressure H2O is a polar solvent, but if the temperature and pressure are increased, the polarity decreases considerably, and H2O can be used to extract medium to low polarity analytes. ... 

Tomy, G. T. G. A. Stern, 1999. Analysis of C14-C17 Polychloro-n-alkanes in Environmental Matrixes by Accelerated Solvent Extraction-High-Resolution Gas Chromatography/EIectron Capture Negative Ion High-Resolution Mass Spectrometry, Anal. Chem. 71 4860-4865. 

For many years, the traditional sample preparation methods, such as the Soxhlet extraction, were applied. Most of these methods have been used for more than 100 years, and they mostly require large amounts of organic solvents. These methods were tested during those times, and the analysts were familiar with the processes and protocols required. However, the trends in recent years are automation, short extraction times, and reduced organic solvent consumption. Modern approaches in solid sample preparation include microwave-assisted solvent extraction (MASE), pressurized liquid extraction, accelerated solvent extraction (ASE), matrix solid-phase dispersion (MSPD), automated Soxhlet extraction, supercritical fluid extraction (SEE), gas-phase extraction, etc. 

In PLE, solvent is pumped into an extraction vessel containing the sample and is heated (e.g., 60-200°C) and pressurized (3.5-20.0 MPa). The method is also termed pressurized solvent extraction (PSE) and accelerated solvent extraction (ASE). Solvent consumption and extraction time are reduced by increasing the solubility of the analyte in the solvent and increasing the kinetic rate of desorption of the analyte from the sample matrix. 

In this context, studies about the development of relevant analytical methods allowing the detection of pesticide residues in VOO are usually focused on an optimization of the various steps of the analysis process, namely extraction, clean-up, identification, and quantitation of pesticide content. The common extraction methods are Soxhlet extraction, microwave-assisted extraction (MAE), supercritical fluid extraction (SEE), and accelerated solvent extraction (ASE). Cleanup methods include SPE, matrix solid-phase dispersion (MSPD), and gel permeation chromatography (GPC). 

A relatively new automated extraction method is PLE, also called accelerated solvent extraction (ASE), which is based on an extraction under elevated temperature (50-200°C) and pressure (3-205 bar) during a short period of time (5-15 min). This technique has been used for the extraction of phenolic compounds from foods such as vegetables and fruits. In PLE, a solid sample is packed into the extraction cell and analytes are extracted from the matrix with conventional low-boiling solvents or solvent mixtures at elevated temperatures up to 200°C and pressure (30-200 bar) to maintain the solvent in the liquid state [61]. 

Accelerated solvent extraction (ASE) is a relatively recent advance in sample preparation for trace environmental analysis. This techiuque uses conventional solvents at elevated pressures and temperatures to extract solid samples quickly. The process takes advantage of the increased analyte solubilities at temperatures well above the boiling points of common solvents. Under these conditions, the kinetic processes for the desorption of analytes from the matrix are accelerated. Currently a commercial unit is available in which automated extractions can be carried out on 24 samples sequentially (Richter et al., 1995, 1996). This technique offers some significant advantages over SEE and MAP. SEE uses supercritical CO2, which is a nonpolar fluid, whereas MAP requires the presence of a polar solvent that couples with microwave to promote heating. By comparison, ASE uses the same solvent as traditional Soxhlet extractions, which means a (firect transfer of methodology is feasible without any of the restrictions or limitations of the two other methods. Method development time is therefore shortened. 

Pressurized liquid extraction (PLE) is also known as pressurized solvent extraction (PSE), enhanced solvent extraction (ESE), pressurized fluid extraction (PEE), or accelerated solvent extraction (ASE ) in the literature. PLE is considered an environmentally friendly extraction technique because it requires only small volumes of solvents. PLE was primarily used for the extraction of environmental samples, such as soils and sediments. Elevated temperatures (usually between 50 and 200 °C) and pressures (between 10 and 15 MPa) are used in closed vessels, which allow extractions to be completed in a very short time. High pressure allows the solvent to remain in its liquid state even at temperatures above its boiling point, and forces it into the matrix pores. High temperatures decrease the solvent viscosity and increase metabolite solubilization, the diffusion rate, and mass transfer kinetics, thus facilitating desorption of the analytes from the plant material. Most PLE applications reported in the literature employ the same organic solvents as those commonly used in conventional solid-liquid extraction techniques. When water is used as the extraction solvent, the technique is referred to as pressurized hot water extraction (PHWE). Extractions are carried out in stainless steel extraction cells of various volumes (typically 1-250 mL). One extraction cycle is generally applied for 5-20 min at temperatures ranging from 50 to 140 °C in the vast majority of applications. 

The mode of extraction for PAHs is highly dependent on the matrix. For solid-based matrices such as food samples, sediments, soil, marine organisms, etc. extraction methods such as Soxhlet extraction with nonpolar solvent [35 6], hollow fiber membrane solvent microextraction (HFMSME) [10], pressimzed hquid extraction (PLE) [37,38], sonication extraction [3], microwave-assisted extraction (MAE) [3], supercritical fluid extraction, (SEE) [39], accelerated solvent extraction (ASE) [40], cold extraction [41], soxtec extraction [42], microwave-assisted alkaline saponification (MAAS) [43], dynamic microwave-assisted extraction (DMAE) [44], add-induced cloud point extraction (ACPE) [45], methanolic saponification extraction (MSE) [7], etc. are employed. Of all these, Soxhlet extraction is the most common for solid samples and has achieved excellent extraction with high-level recovery but its setback is the high consmnption of solvent and time associated with it. 

In the static mode, the sample is placed into an extraction vessel, filled with a supercritical fluid at the appropriated temperature and pressure, and allowed to stand for a period. When the extraction is complete, the supercritical fluid is released through a trap to collect the analytes. Static extraction allows analytes with slow mass transfer time to be solvated by the SF. In addition, the use of a known concentration of modifier is possible by direct addition of the modifier to the extraction cell. The main limitation of static extraction is its inability to perform an exhaustive extraction. As in static headspace GC, and the traditional liqnid-liquid extraction, as a result of the equilibrium of the analyte between the matrix and SF, one extraction can not exhaustively extract the analyte from the matrix. Consequently, it is often necessary to perform multiple static extraction. The use of SFE has been decreasing over the years in part due to the growth of accelerated solvent extraction (ASE), which employs much of the same instrumentation and methodology of Sra. 

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