Pressurized fluid extraction instrumentation

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. 

Supercritical fluid extraction can be performed effectively with very simple systems. Figure 5 displays the basic components of an effective analytical SFE device. There are relatively few commercial suppliers of dedicated supercritical fluid extraction instrumentation. Table 7 shows the companies that promote SFE instrumentation as of the writing of this chapter. Some of the more traditional instrument manufacturers such as Hewlett-Packard (7680T SFE), Dionex (SFE 723), and Supelco (SFE-400) have discontinued their SFE lines. Dionex has invested quite heavily into high-temperature/high-pressure solvent extraction devices, and this will be described in the next section. For most purposes, inexpensive and efficient extraction units can be assembled using the basic components shown in Figure 5. 

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. 

See also Atomic Absorption Spectrometry Interferences and Background Correction. Atomic Emission Spectrometry Principles and Instrumentation Interferences and Background Correction Flame Photometry Inductively Coupled Plasma Microwave-Induced Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Countercurrent Chromatography Solvent Extraction with a Helical Column. Derivatization of Analytes. Elemental Speciation Overview Practicalities and Instrumentation. Extraction Solvent Extraction Principles Solvent Extraction Multistage Countercurrent Distribution Microwave-Assisted Solvent Extraction Pressurized Fluid Extraction Solid-Phase Extraction Solid-Phase Microextraction. Gas Chromatography Ovenriew. Isotope Dilution Analysis. Liquid Chromatography Ovenriew. 

The instrumental requirements for supercritical fluid extraction are quite simple. A pump is essential to generate the extraction pressure in a themostated extraction vessel. The soluble sample components are then swept from the vessel through a flow restrictor into a collection device that is normally at ambient pressure. The fluid used for supercritical fluid... 

Comparison of simple methanol extraction, Soxhlet extraction, pressurized liquid extraction (PLE), and supercritical fluid extraction (SFE) shows (Clausen et al., 2003) that DEHP can be extracted relatively easily from dust and that the effectiveness does not differ significantly between the different extraction methods (see Figure 2.4). Selection of the optimal method depends on several circumstances, for example number of extraction cycles, instrument accessibility and the analysis method. However, PLE using cyclohexane/acetone was chosen as the preferred extraction method in the field study. 

In this introductory book chapter, several modem extraction techniques will be described, including supercritical fluid extraction, pressurized liquid extraction, pressurized hot Avater extraction, microwave assisted extraction, membrane-assisted solvent extraction, solid phase micro extraction and stir-bar sorptive extraction. These are techniques that meet many of today s requirements in terms of environmental sustainability, speed and automation. Basic principles of operation as well as method optimization will be discussed and compared for the different techniques. Both analytical and industrial applications will be discussed, together with commercial instruments available on the market. Key references will be given, and conclusions regarding applicability of the different techniques with respect to sample e, target-molecules and analytical vs. large-scale applications. 

The third instrumental approach is the use of supercritical fluid extraction (SEE). A supercritical fluid is a substance at a temperature and pressure above the critical point for the substance. (You may want to review phase diagrams and the critical point on the phase diagram in your general chemistry text.) Supercritical fluids are more dense and viscous than the gas phase of the substance but not as dense and viscous as the hquid phase. The relatively high density (compared with the gas phase) of a supercritical fluid allows these fluids to dissolve nonvolatile organic molecules. Carbon dioxide, CO2, has a critical temperature of 31.3°C and a critical pressure of 72.9 atm this temperature and pressure are readily attainable, making supercritical CO2 easy to form. Supercritical CO2 dissolves many organic compormds, so it can replace a variety of common solvents supercritical... 

Instrument-based extraction techniques such as supercritical fluid extraction (SEE) and pressurized liquid extraction (PEE) offer advantages because of their potential for automation, more selective isolation of residues through tuning of parameters, and on-line clean-up of samples. Their applications have been slowed by the limited number of commercially available instruments, additional extraction costs, and instrumental downtime. Although several applications have been developed using SEE and PEE, these techniques are not widely used in routine laboratories. 

The instrumentation for SFE can be relatively simple as shown in Figure 29-10. Instrument components include a fluid source, most commonly a lank of carbon dioxide a syringe pump having a pressure rating of at least 400 atm and a flow rate for the pressurized fluid of at least 2 mL/min a valve to control the flow of the critical fluid into a heated extraction cell having a capacity of a few milliliters and an exit valve leading to a flow restrictor that depressurizes the fluid and transfers it into a collection device. In the simplest instruments, the flow restrictor is 10 to 50 cm of capillary tubing. In modern sophisticated commercial instruments, the restrictors are variable and controlled manually or automatically. Several iastrument manufacturers offer various types of SFE apparatus. ... 

Supercritical fluid extraction (SFE) is the most widespread of these methodologies. SFE is based on the use of a fluid at temperatures and pressures near the critical point. It comprises an extraction phase where the analyte is extracted from the sample matrix, followed by collection or trapping of the analytes, which might be coupled online into an analytical instrument, usually a liquid chromatograph. Off-line collection of the analytes can also be achieved after depressurizing of the supercritical fluid (SF) into a collection device such as an empty vessel, a vessel containing a small volume of solvent, solid-phase or solid-liquid phase traps, or a cryogenicaUy cooled capillary (reviewed by Turner etal. ). 

Supercritical fluid extraction (SFE) is an extraction procedure which utilizes solvents in their supercritical state as extractive agents. These supercritical fluids have similar densities to liquids, but lower viscosities and so higher solvation power. Supercritical fluids constitute an acceptable alternative to conventional liquid solvents in the analytical extraction of enviromnental samples [137]. Supercritical fluids are obtained in commercially available instruments, applying high temperatures and pressures to the solvent to ensure conditions above the critical point. The sample is located in an inert extraction cell, where the supercritical fluid is pumped. 

SEE is an instrumental approach not unlike PLE except that a supercritical fluid rather than a liquid is used as the extraction solvent. SFE and PLE employ the same procedures for preparing samples and loading extraction vessels, and the same concepts of static and dynamic extractions are also pertinent. SFE typically requires higher pressure than PLE to maintain supercritical conditions and, for this reason, SFE usually requires a restrictor to control better the flow and pressure of the extraction fluid. CO2 is by far the most common solvent used in SFE owing to its relatively low critical point (78 atm and 31 °C), extraction properties, availability, gaseous natural state, and safety. 

Off-line SFE is conceptually a simple experiment to perform and requires only relatively basic instrumentation. The instrumental components necessary include a source of fluid, most often CO2 or CO2 with an organic modifier, a means of pressurizing the fluid, an extraction cell, a method of controlling the extraction cell temperature, a device to depressurize the supercritical fluid (flow restrictor), and a device for collecting the extracted analytes. 

Modifier Pump. The first feature in our adapted design is the introduction of a liquid pump via an instrument controlled VALCO (Model E04, Valeo Instruments, Houston, TX), four position selection valve. We have used an LKB Model 2150, dual piston pump for pumping modifier and entrainer fluids (LKB-Produkter AB, Bromma, Sweden). However, any suitable liquid pump could be substituted. Only pure fluids such as carbon dioxide have been introduced with the Suprex system syringe pump. With the addition of this second pump to deliver liquids, modifier is introduced directly into the extraction vessel. A wide range of alternative fluids and fluid mixtures can be rapidly selected with this dual pumping option. The criteria for selection of a modifier pump include the ability of the pump heads to withstand pressures in the range of 100 to 300 atm and interfacing capabilities, i.e. the ability to be turned on and off by the Suprex contact closure controls. 

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