Accelerated solvent extraction instrumentation

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

This chapter covers techniques for the extraction of semivolatile organics from solid matrices. The focus is on commonly used and commercially available techniques, which include Soxhlet extraction, automated Soxhlet extraction, ultrasonic extraction, supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), and microwave-assisted extraction (MAE). The underlying principles, instrumentation, operational procedures, and selected applications of these techniques are described. In a given application, probably all the methods mentioned above will work, so it often boils down to identifying the most suitable one. Consequently, an effort is made to compare these methodologies. 

The accelerated solvent extraction (ASE) system introduced by Dionex uses standard solvents at elevated temperatures and pressures to increase extraction efficiency. Samples are placed in stainless-steel extraction vessels that are loaded into the ASE that has been programmed for the extraction protocol. The instrument allows for the unattended extraction of 24 samples. The initial units allowed for solvent blending by premixing solvents before they were placed into the ASE. Recent modifications allow solvent blending to be accomplished in-line. There has been some controversy about the use of the name ASE because it points to instrumentation from one company and other companies have introduced competing products. It has been proposed that the ASE technology be more correctly referred to as pressurized fluid extraction because ASE denotes a commercial device. 

A recent advance is accelerated solvent extraction (ASE), a method that uses high temperature and pressure to push an organic solvent through a solid material and to collect the eluent in a vial (Fig. 9.2). The instrument, made by Dionex, is automated and may run 30 samples at once. The instrument can process one sample every 15 min with extraction efficiencies equal to that produced by Soxhlet extraction in 12 h (Dionex, Product Literature, Appendix). The extraction does not use supercritical fluids but consists of using elevated... 

Since pressurized fluid extraction (PFE), also known as accelerated solvent extraction (ASE ), is a relatively new technique, the commercial availability of PFE instruments is limited. A commercial PFE system ( ASE 200 ) currently available is a fully automated sequential extractor developed by the Dionex Corporation, USA. This mainly consists of a solvent-supply system, extraction cell, oven, collection system and purge system, all of which are under computer control. A schematic diagram of a PFE system is shown in Figure 7.15. This system (ASE 200) can operate with up to 24 sample-containing extraction vessels and up to 26 collection vials, plus an additional four vial positions for rinse/waste collection. 

Yes, there have been comparative studies in which the percent recovery has been measured using not only SFE but also ASE and comparing these results to percent recoveries from the more conventional Soxhlet extraction (S-LSE). Generally, these studies are done on certified reference samples or on grossly contaminated samples. We will discuss two studies from the recent analytical chemistry literature. The first study compared the efficiencies of SFE, high-pressure solvent extraction (HPSE), to S-LSE for removal of nonpesticidal organophosphates from soil (46). HPSE is very similar to accelerated solvent extraction however, we will reserve the acronym ASE for use with the commercial instrument developed by Dionex Corporation. HPSE as developed by these authors used parts available in their laboratory.. The authors compared S-LSE with SFE and HPSE for extraction of tricresyl phosphate (TCP) and triphenyl phosphate (TPP) from soil. Molecular structures for these two substances are as follows ... 

Sampling, sample handling, and storage and sample preparation methods are extensively covered, and modern methods such as accelerated solvent extraction, solid-phase microextraction (SPME), QuEChERS, and microwave techniques are included. Instrumentation, the analysis of liquids and solids, and applications of NMR are discussed in detail. A section on hyphenated NMR techniques is included, along with an expanded section on MRI and advanced imaging. The IR instrumentation section is focused on FTIR instrumentation. Absorption, emission, and reflectance spectroscopy are discussed, as is ETIR microscopy. ATR has been expanded. Near-IR instrumentation and applications are presented, and the topic of chemometrics is introduced. Coverage of Raman spectroscopy includes resonance Raman, surface-enhanced Raman, and Raman microscopy. 

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. 

Special, fully automated instruments are available for ASE these include an extraction cell (1 up to 100 ml), which is maintained at a temperature between 80 and 200°C, into which a solvent is pumped and maintained at 10—20 MPa for some minutes. Then, a second volume of solvent carries the extract into a collection vial finally, the solvent is removed by flushing an inert gas. The main advantages of ASE are the high extraction yield combined with short extraction time and reduced solvent consumption. For the separation of volatile and semi-volatile components, accelerated solvent extraction gives recoveries comparable to those obtained with Soxhlet and other solvent-extraction techniques... 

Accelerated solvent extraction (ASE), also known as pressurized solvent extraction, is an instrumental technique that allows the extraction of solid or semisolid samples with organic solvents at temperatures above the boiling point of the solvent. In addition to the increased efficiency of... 

A recent study published in the Chinese Journal of Instrumental Analysis, Fenxi Ceshi Xuebao, showed a detection limit of 500 ng of Sulfur Mustard (HD) by using accelerated solvent extraction-gas chromatography (ASE-GC) coupled with a flame photometric detector (EPD) in the sulfur mode, in soil. In this case, the study showed evidence that ASE results in better recoveries and sensitivity than liquid solid extraction (LSE) [50]. In 1996, a paper was published on a method for the analysis of Lewisite through derivatization of the compound before introduction into a gas chromatograph. In order to simplify the derivatization process, a tube packed with absorbent was used for collection of airborne vapors. If a positive response occurs when screening analytes using a GC coupled with an FPD, then the same sample can be analysed using a GC equipped with an AED for confirmation based on the elemental response to arsenic (in the case of Lewisite) and sulfur (in the case of Sulfur Mustard) within the appropriate GC retention time window [54]. 

A typical procedure for TLC/HPTLC analysis of inks is as follows. A sample of an ink line, of - lOmm, is scraped from the document and dissolved in 10 pi of an appropriate solvent in a glass capillary (the extraction procedure can be accelerated by heating the capillary at 100°C for 15 min). The sample is spotted on a preconditioned or prewashed silica plate and eluted with a solvent. Several mobile phases can be used, depending on the kind of writing instrument examined. 

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