Supercritical Fluid Methods and Protocols (Methods in Biotechnology)

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However, there are few data to substantiate its efficacy in this role. The concept of supercritical fluid extraction SFE was introduced in Chapter 1. Extraction with supercritical carbon dioxide CO2 as the solvent has been used to isolate components from different matrices such as biological and environmental samples 2. The commercial process of extraction of caffeine from coffee using supercritical CO2 was patented by Zosel in 3.

The analytical SFE of caffeine from coffee has been reported by other workers using SFE coupled to supercritical fluid chromatography 4 , nuclear magnetic resonance spectroscopy 5 , infrared spectroscopy 6 , and high performance liquid chromatography HPLC 7. However, the use of a nonpolar supercritical fluid, such as CO2, does not exhaustively extract caffeine from instant coffee. As has been reported elsewhere 2 , the polarity of the supercritical fluid can be increased by the addition of a polar organic solvent, for example, methanol.

Analysis of the extracts is done by HPLC with ultraviolet detection. From: Methods in Biotechnology, Vol. Schematic diagram of the SFE apparatus. Materials 2. SFE 1. Two reciprocating pumps see Fig. A back-pressure regulator see Fig. A recirculating water bath containing an ethylene glycol mixture, which is passed through a jacket that encases the CO2 pump-head only see Fig.

An extraction cell see Fig. Analyte collection occurs during depressurization into a glass collection vial containing a suitable organic solvent methanol fitted with a rubber septum through which two holes are pierced see Fig. The purpose of the latter is to prevent loss of analyte from the collection vial and to vent the escaping gaseous carbon dioxide. HPLC-grade methanol. HPLC 1. Reciprocating pump Gilson, model , Anachem Ltd. SFE of Caffeine 19 3. An ultraviolet-visible detector Jasco, UV for monitoring the response at a wavelength of nm.

Sample 1. Instant coffee granules were purchased from local retail outlets in both decaffeinated and caffeinated forms. Method 3. Sample Preparation 1. Mix one part of the ground instant coffee with one part of Celite see Note 1. Turn on the electrical supply to the SFE system, including the recirculating water bath. Allow 30 min for cooling of the CO2 pump-head. Take an extraction cell see Note 2 and tighten, using a wrench, an end-cap on one end only and then weigh the cell.

Tighten the other end-cap on to the cell with the wrench and insert the capped cell into the oven. Plumb the cell into the SFE system. This requires the use of a wrench to ensure a suitable connection. Set SFE operating parameters: flow rate of liquid carbon dioxide, 1. Allow the system to operate for a few minutes to establish a working system.

Before the extraction commences, preheat the extraction cell containing the sample to the preset temperature for 10 min see Note 3 , then undergo a static extraction no flow of CO2 at the operating conditions for 5 min and, finally, a dynamic extraction flow of CO 2 and methanol for 1 h. After the allotted extraction time, remove the collection vial from the system and back-flush the C18 SPE cartridge with 2 mL of fresh methanol see Note 4.

Extract further samples using the stated parameters. Analysis of Coffee for Caffeine 1. Quantitatively transfer the contents of the collection vial into a mL volumetric flask and adjust to the required volume with a water:methanol mixture for decaffeinated products only. For caffeinated products, pipet 1 mL of 20 Dean et al. HPLC chromatogram of caffeine extracted from decaffeinated instant coffee.

This entails running a series of 4 to 5 caffeine standards of known concentration in methanol. There should be a linear relationship between absorbance and caffeine concentration over the concentration range of interest. The caffeine peak appears at a retention time of approximately 11 min. Analyze for the unknown levels of caffeine in the coffee extracts. Typical caffeine levels in commercial instant coffees using four varieties for which decaffeinated and caffeinated were available and a single variety for which only decaffeinated was available determined by off-line SFE—HPLC ranged from 0.

Typical chromatograms obtained for decaffeinated and caffeinated coffee extracts are shown in Figs. SFE of Caffeine 21 Fig. HPLC chromatogram of caffeine extracted from caffeinated instant coffee. Notes 1. Ensure the extraction cell is suitable for its purpose, that is, able to withstand high pressure and does not leak. After insertion of the extraction cell into the oven, allow sufficient time for the cell and its contents to reach the preset temperature.

Ten minutes was considered to be suitable in this experiment. This will ensure that quantitative analyses are performed. Lopez-Ortiz, A. Dean, J. Blackie Academic and Professional, Glasgow, U. Zosel, K. Patrick, E. Braumann, U. Heglund, D. Ndiomu, C. Acta , — Pensabene and Walter Fiddler 1. Introduction Supercritical fluid extraction or SFE see Chapter 1 is used to isolate pesticides from environmental samples, fruits and vegetables.

However, the use of this technique for the extraction of residues, such as nitrosamines at the ppb level, in cured meat products is relatively recent. The fact that nitrosamines induce cancer in at least 40 different animal species, including primates 2 , makes it likely that these compounds would also be active in humans. This accounts for the regulatory concern, the monitoring of, and establishment of tolerance or action levels for nitrosamine-containing foods.

The two SFE methods described in this chapter are alternatives to distillation 3—5 and solid-phase extraction or SPE 6 methods currently in use that employ considerable amounts of organic solvents, principally halogen-containing ones. Unlike the distillation methods, without the addition of a nitrosation inhibitor, SFE is not as susceptible to artifactual nitrosamine formation. These SFE methods for isolating volatile nitrosamines include N-nitrosopyrrolidine formed in bacon as a result of frying 7 , N-nitrosodibutylamine 8 and the semivolatile, N-nitrosodibenzylamine 9—11 , which is found primarily on the surface of boneless hams that are wrapped with rubber-containing elastic nettings.

These methods are applicable to a wide range of cured meat products, from high fat bacon to lean boneless ham. For these three nitrosamines, and for the other Mention of brand or firm names does not constitute an endorsement by the U. Department of Agriculture over others of a similar nature not mentioned. Interfacing this TEA to a gas chromatograph allows the separation and permits specific detection of N-nitroso compounds at the subnanogram level. SFE with off-line trapping on a commercial SPE cartridge is employed for the isolation of nitrosamines in both types of products.

With a slight modification, the method for fried bacon is also applicable to its drippings. The procedure presented herein is simple, rapid, solvent-sparing, and offers a reproducible means for extracting nitrosamines from these complex food matrices. Materials 1. Extraction vessels were connected to the system with hand-tightened, slip-free connectors Keystone Scientific, Bellefonte, PA.

A diagram of this instrument is shown in Fig. Supercritical-grade CO2, without helium headspace. High pressure 10, psi extraction vessels, 24 mL capacity Keystone Scientific. Tamping rod and polyethylene frits for mL extraction vessels Applied Separations. The column used was a 2.

Diagram of the supercritical fluid extraction system. The column used was a 1. Method 1. Comminute and then mix the meat sample thoroughly to obtain a representative sample. All samples are to be analyzed in duplicate. Weigh 5. Add mg of propyl gallate to the sample to prevent artifactual nitrosamine formation. Fortify the sample with 0. Add 5. Seal one end of the high-pressure extraction vessel and label it on top. Add the dry, free-flowing sample mixture to the extraction vessel prepacked with a plug of polypropylene wool see Note 5. Tightly compress the mixture with a tamping rod to ensure uniform supercritical fluid flow.

Add a second plug of polypropylene wool to the extraction vessel and compress in place with the tamping rod see Note 6. Seal bottom end of extraction vessel. Install the extraction vessels in the SFE oven with the end labeled top connected to the upper fittings Fig. Attach 6 mL SPE cartridges containing 1. Attach the flow meter—gas totalizer to the SPE cartridges with flexible tubing. Ensure there are no leaks of gas at the connections.

Close the outlet and vent valves; open the inlet valves. Adjust the pressure to a final setting of 10, psi bar. After the min heating period, open the outlet valves to direct flow through the micrometering valve module to the SPE cartridges. Use the micrometering valves to establish and maintain a 2. After 50 L per vessel are recorded on the gas totalizer, close the inlet and outlet valves and depressurize the SFE vessels by slowly opening the vent valves.

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Remove the extraction vessels from the oven, and attach Luer adapters to the upper slip-free connectors of the extractor. Attach a 1-mL glass syringe to each adapter and flush any trace residues of analyte-lipid remaining in the lines with 0. SFE of Nitrosamines 27 Remove the SPE cartridges containing the analyte—lipid mixture from the micrometering valve collection assembly. Hold the cartridges below the micrometering valve and rinse the external system with 0.

Collect the eluate in mL concentrator tubes. Attach a micro-Snyder column to the concentrator tube and concentrate solvent to approximately 0. Dilute to a final volume of 1. Reported performance criteria for normally incurred nitrosamines in fried bacon 15 are NPYR, range, 0. Total time to prepare duplicate samples for quantitation is about 1 h; GC-TEA analysis time is approximately 25 min. It was sieved to a particle range of 70— mesh before use. Hydromatrix: Sieved at 30—40 mesh to remove fine particles. Caution: N-nitrosamines are potential carcinogens. Exercise care in handling these compounds.

Nitrosamines were synthesized from the corresponding amine and sodium nitrite as follows: cool an equimolar amine—hydrochloric acid solution with ice. Slowly, add a twofold excess of an aqueous solution of sodium nitrite to the amine—acid solution. Extract the nitrosamine three times with diethyl ether.

Dry the combined extracts over anhydrous sodium sulfate, then filter and concentrate under a stream of nitrogen. Distill the nitrosamine under vacuum Add the sample mixture to the extraction vessel in approximately four equal parts, compressing after each addition. If there is more than a 1-cm space between the end of the compressed wool and the top of the extraction vessel, fill the space with additional polypropylene wool. Add the silica gel to the cartridge followed by a polyethylene frit.

Cut a 4-mm hole in another frit using a No. This will prevent sample loss during decompression of the CO 2. Analyze all samples in duplicate. Nitrosamines in the individual samples are corrected for recovery of the NDPA internal standard. Preussmann, R. Tricker, A. Fine, D.

Acta 78, — Greenfield, E. Sen, N. Pensabene, J. Food Sci. IARC Sci. Fiddler, W. AOAC Int. Maxwell, R. SFE of Nitrosamines 29 Fuerst 1. In the United States, the Food and Drugs Administration FDA has set the tolerance level for residues of MGA in edible tissues at 25 ppb based on evidence that residues at or below this concentration do not elicit a hormonal response 1 , whereas in the European Union EU the residue limit for this steroid in animal products is 0 ppb 2.

All of the reported methods use large amounts of organic solvents, many of which are halogenated. Department of Agriculture to detect MGA in bovine fat tissue requires 1. This is a matter of concern because the U.

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Environmental Protection Agency EPA has mandated that Federal laboratories and others reduce or eliminate the use of certain organic solvents 8. Hence solvent-sparing technologies must be investigated to determine their suitability for regulatory laboratories. Mention of brand or firm names does not constitute an endorsement by the US Department of Agriculture over others of a similar nature not mentioned. Chemical structure of melengestrol acetate. The fundamental principles of supercritical fluid extraction SFE have been covered in Chapter 1.

Extraction with supercritical fluids has been used by others to isolate steroids such as androsterone from boar fat 9. In that study, the steroid was collected off-line [after carbon dioxide CO2 decompression] together with coextracted fat. This method of analyte collection requires several post-SFE clean-up operations to separate the androsterone from coextracted fat prior to chromatographic analysis. Maxwell et al. This technique is illustrated in Fig. Analytes such as steroids are retained on the in-line sorbent bed while fat and other fat-soluble coextractables are deposited in an off-line vial after CO2 decompression thereby eliminating the need for multiple post-SFE clean-up operations.

Recoveries of MGA from fortified tissues were Table 1 shows calculated concentration values of incurred residues of MGA from bovine fat tissues that compared favorably to those obtained by the FSIS procedure Schematic drawing of high pressure extraction vessel showing layering of in-line trap, sample mixture and presample trap. Note that the total 34 Maxwell et al.

The SFE apparatus is equipped with a thermocouple to monitor extraction vessel temperature. The use of this device obviates the need for helium-pressurized CO2, which is required for standard operation with a noncooled pump-head. The extracted fat is collected off-line in 9-mL vials fitted with septa.

Hydromatrix or Celite part no. Alumina Al2O3 —activated, neutral, Brockmann I catalog no. Louis, MO , used as received. Solid-phase extraction SPE columns 6 mL containing 1. Supercritical fluid chromatography-grade CO2 with a diptube and no helium headspace Scott Specialty Gases. Polypropylene wool from Aldrich Chemical Co. SFE of Melengestrol 35 Fig.

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HPLC chromatograms of supercritical CO2 extracts of A control sample of perirenal fat tissue and B visceral fat tissue animal number containing incurred residues of melengestrol acetate or MGA reported concentration, 20 ppb; determined concentration, Heptafluorobutyric acid anhydride or HFBA cat.

Microreaction vessel cat. Quantitation of MGA is accomplished by comparison of peak heights or areas or both with external standards. The final temperature is held for 10 min. Place 1. Add the fortified tissue to 4. Cap and seal one end of an SFE high pressure vessel and label that end top. Pack the extraction vessel tightly see Note 6 in the following sequence relative to the top of the vessel: a plug of polypropylene wool, two polyethylene frits, 2 g of neutral alumina analyte trap , a polyethylene frit, fortified or incurred tissueHydromatrix mixture dry, free-flowing sample mixture , a polyethylene frit, 3 g of alumina presample trap - see Note 7 and a polyethylene frit Fig.

Cap bottom end of vessel. The SFE inlet, outlet and vent valves should be closed and the micrometering valves set to a minimum flow rate. Install the packed extraction vessels in the SFE oven with the end labeled top connected to the upper slip-free fittings and attach the built-in thermocouple to one extraction vessel see Note 8 and Chapter 3, Fig.

Attach a 9-mL vial to each micrometering valve off-line interface for fat collection. When the vessel set point temperature is reached, open the inlet valves and increase the pump pressure to 10, psi or bar see Note 9. Equilibrate the system with a 5 min static holding period. After 5 minutes, open the outlet valves. After 40 L are recorded by the totalizer, close the inlets valves and depressurize the extraction vessels under controlled flow conditions using the micrometering valves see Note Attach an empty 6-mL SPE column fitted with a polyethylene frit to a stand.

Directly below this column attach a 6 mL SPE column containing 1. Set aside until step After extraction vessel decompression, remove the vessel s from the SFE oven and uncap the end labeled top see Note Remove and discard the polypropylene wool and frits. Compact the sorbent by tapping the sides and top of the SPE column with a spatula, then layer the top of the sorbent bed with 0.

Evaporate the MeOH in the vial to dryness under a nitrogen stream. Transfer contents of vial to a 0. Evaporate the contents of the vessel to dryness at room temperature under a nitrogen stream. Vortex the vessel and centrifuge. Performance criteria for normally incurred MGA in bovine fat tissue are shown in Table 1. Total time to prepare the sample for quantitation is approximately 1 h. Fortification solutions containing 34, 17, and 8.

Hold the fortified tissue at room temperature for 10 min before beginning step 2 in order to allow permeation of MGA into the tissue and for evaporation of the MeOH. SFE of Melengestrol 39 6. Compress the material tightly in the vessel with the tamping rod after adding each successive layer.

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Refrigerate the packed vessel to prevent analyte loss if it is not to be immediately extracted by SFE. The purpose of the presample trap is to prevent any contaminants from the SFE pump or the CO2 cylinder from reaching the in-line analyte trap. The vessel temperature is monitored separately from the oven temperature in order to ensure reproducible analyte recovery.

Monitor vessel temperature on thermocouple display not oven temperature readout to ensure that vessel temperature does not exceed the set point during vessel pressurization. Do not use the vent valves to depressurize the system. It is neither necessary to clean the transfer lines from the SFE vessel to the micrometering valves after each use, nor is it required to replace the off-line fat collection vials on a daily basis.

However, in the event that the transfer lines are to be cleaned, attach Luer adapters to the upper slip-free connectors in the oven and attach a 1-mL syringe filled with 0. Flush fat residues in transfer lines into the off-line collection vials.

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  • Anonymous Melengestrol acetate clearances broadened. News, August 15, p. Heitzman, R. Ryan, J. Chichila, T. Pollution Prevention Strategy. High Resol. Parks, O. Stolker, A. Hale 1. Introduction Polychlorinated biphenyls PCBs are of great concern to the scientific and regulatory communities due to their tendency to accumulate to toxic levels in the edible tissues of fish and other organisms 1—4. PCBs are nonpolar compounds that can partition into the lipid reservoirs of edible tissues causing damage to ecosystems and human health 5,6.

    Despite significant progress in environmental reform, extraction methodologies required to isolate PCBs continue to rely heavily on environmentally deleterious liquid organic solvent extraction methods such as Soxhlet extraction, sonication, and column elution 7—9. These techniques are laborious, tedious, analyte-nonselective, and require copious volumes of organic solvents.

    Common solvents are typically toxic or flammable and ultimately must be disposed of as hazardous waste. Traditional solvent extracts obtained require multiple postextraction purification steps, such as gel permeation chromatography GPC , florisil, and silica column clean-up These steps contribute further to the hazardous waste disposal problem facing environmental laboratories.

    The entire process is paradoxical in that it contradicts the intended goal of these procedures, that of improving environmental quality. By contrast, supercritical fluid extraction or SFE Chapter 1 has emerged in recent years as a more environmentally benign analytical technique that promises to significantly improve the extraction of trace organic pollutants, such as PCBs, from environmental samples 11, The practical advantages of SFE for PCB determinations in environmental samples include minimal sample manipulation, rapid extractions 30—60 min , improved analyte selectivity and From: Methods in Biotechnology, Vol.

    The vast majority of environmental research has focused on SFE of abiotic matrices such as soils, sediments, sludges, and fly ash 13— Comparably little research has been conducted in applying SFE to trace-level organic pollutant determinations in aquatic biota samples 11,16, Complete removal of water from the sample is critical for SFE because of the potential to freeze and plug the restrictor and cryogenic trap during extraction.

    Further, because of the negligible miscibility of supercritical phase CO2 and water SFE of PCBs 43 considerable time hours vs days and solvent milliliters vs liters compared to conventional liquid solvent-based techniques and is capable of selectively extracting PCBs from fatty fish tissue samples. Organic solvents hexane, isooctane, benzene, n-propyl alcohol, acetone, methylene chloride, methanol certified for pesticide residue trace analyses.

    Ultrahigh purity helium and hydrogen minimum purity Soaking overnight is preferred. Remove glassware from Contrad 70 solution, rinse with deionized water and allow to air dry. Before preparing samples, rinse all sample contact surfaces with a suite of organic solvents ranging in polarity from moderately polar to nonpolar. A typical sequence is methanol, acetone, methylene chloride, and hexane. Edible fish tissue sample handling and preparation: immediately after collection, wrap the fish in solvent-rinsed aluminum foil, pack on ice, and transport to the laboratory. Remove edible fillet tissue and place in a clean, preweighed stainless steel freeze-dryer pan see Note 5.

    Reweigh the pan and wet sample to determine percent moisture after freeze-drying. Cover the samples with aluminum foil and freeze overnight in preparation for drying. Freeze-drying samples: rinse the freeze-dryer thoroughly with a methanolsoaked, lint-free disposable towel and allow it to completely dry before introducing samples. Remove sample pans from the freezer and place them immediately into the freeze-dryer.

    Peel back one corner of the foil to allow complete sublimation of sample water during freeze-drying. During freeze-drying, a positive pressure of nitrogen 0. Samples typically require 24—48 h to dry thoroughly see Note 6. Sample homogenization: after drying, store foil-covered samples in a desiccator. Place each individual sample separately into a blender and homogenize at high speed until a powderlike consistency is achieved see Note 7. Activation of neutral alumina before SFE: Activate neutral alumina by pouring a 2- to 3-cm layer of alumina into a clean stainless steel freeze-drying pan or Pyrex dish.

    Preparation of surrogate and internal standards: prepare surrogate standard s by dissolving known amounts of PCB congeners 30, 65, and in hexane in a clean volumetric flask. An internal standard should be chosen and prepared similarly for use in quantitating PCBs in the sample see Note 8. Pre-SFE sample preparation: remove tissue samples from the freezer and allow them to warm to room temperature in the sample jars. Solvent rinse stainless steel extraction vessels 10 mL; see Subheading 3. Allow vessels to completely dry for several minutes under a fume hood.

    Tare the vessel on an analytical balance. Introduce the sample into the vessel using a clean spatula by gently scraping tissue from the jar and guiding it into the funnel in small amounts. Remove any spilled sample material from the vessel rim and weigh at periodic intervals until the desired sample weight is achieved usually 1 g.

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    Again, remove excess sample material from the top rim spilled during vessel filling before recording the final sample weight see Note 9. Using a graduated pipette, add the desired amount of surrogate standard directly to the top of the sample to assess the efficacy of the technique and account for procedurally related analyte losses. Allow carrier solvent to evaporate before continuing see Note Addition of neutral alumina: remove alumina from the oven and transfer to a clean to mL beaker, cover with clean aluminum foil and allow to cool to room temperature in a desiccator see Note Once cooled, slowly pour the alumina directly into the exit end of the extraction vessel, on top of the sample, until the vessel is filled completely see Fig.

    Gently tamp the vessel periodically during alumina addition to compact the sorbent and eliminate voids. The final sorbent level should be ca. Completely remove excess sorbent from the rim of the vessel opening see Note 9. Cap the vessel with a PEEK frit and seal with the crimping wrench. Load the vessels into the SFE sample carousel. Preparation of the cryogenic trap: disassemble the trap by removing both end caps and freeing the stainless steel center piece see Note If the trap has been used previously for a different suite of analytes, and contains sorbent incompatible with PCB trapping, blow out this material into an appropriate disposal receptacle using compressed air.

    Solvent rinse the trap to remove residual material from the inner surface. Cap the bottom end exit end and insert a small plug of glass wool into the top end entrance end , compressing it to the bottom with a clean spatula or glass rod to retain the trapping sorbent during analyte collection.

    Cap the top end and reattach the assembly to the AccutrapTM module. Sample extraction: enter the desired extraction parameters into the SFE unit using the key pad on the front of the instrument. The optimum parameters for extraction of PCBs from fish tissue with this configuration are: 10 min initial static 46 Gaylor and Hale Fig.

    Diagram of an SFE vessel showing the orientation of sample, alumina and direction of CO2 flow and dissolved analytes during extraction. After desorption, the remaining isooctane and analytes are purged from the trap with nitrogen. This prevents analyte carry-over between collection vials and promotes quantitative analyte recovery see Note Amend the extract with internal standard s before chromatographic analysis for use in quantitation of sample PCBs see Note After quantitation, PCB concentrations in the sample are typically normalized to the recovery of surrogate compounds.

    Quality assurance or quality control: continuously monitor quality assurance and control by extracting spiked blank matrices interspaced between real samples to assess analyte carryover, laboratory contamination and recovery of surrogate compounds in all samples. Spiked blanks can also be used to establish analyte solubility under a given set of extraction conditions and ensure that quantitative recoveries of surrogate compounds are obtained in the absence of matrix effects. Extract sample replicates and standard reference materials SRMs periodically to certify accuracy and precision of the protocol.

    Inject PCB standards containing congeners representing all degrees of chlorine substitution i. Two balances were used for this work, one high weight range for sample and extraction vessel weighing Mettler and the other for standard s preparation Ohaus. PCBs 30, 65, and have been used extensively as surrogate standards during development of this method. Other congeners are potentially suitable provided they are also absent from commercial Aroclor mixtures, thus not occurring in environmental samples Recently, considerable SFE optimization work has been completed using a PCB by-product standard containing PCB congeners 1, 3, 7, 30, 50, 97, , , , , and These compounds have proven valuable for assessing extraction efficiency as a function of both molecular weight and degree of chlorination from spiked blanks and real-world samples containing minimal incurred PCBs i.

    Again, the majority of these congeners are either absent from technical Aroclor mixtures, or present at less than 0. The major consideration should be that the surrogate compounds represent the range in physical and chemical properties of the analytes of interest. This will facilitate larger desorption volumes if needed.

    Use of these vials also eliminates the need for any solvent rinsing of the trap between samples. Considerable flexibility exists here for the analyst. Any data system capable of analog to digital signal conversion with subsequent peak area integration and quantitation should be adequate. A glass fillet board is recommended for use during fish dissection because it is inert, easy to clean, and will withstand rinsing with organic solvents. The fillet board and knife should be rinsed thoroughly with deionized water and the solvent regime described in Subheading 3.

    The time required for complete drying of tissue samples will vary depending upon sample amount, density, water content and freeze-dryer efficiency. Samples should be checked at to h intervals by probing with clean spatulas. Drying is complete in less than 48 h in most cases. Attempts to dry tissue samples with chemical desiccants during SFE method development failed. It was possible to obtain a sample with a manageable powderlike consistency that appeared visually dry.

    This could be due in part to the elevated temperatures at which the extractions were conducted. Algaier et al. In light of these data, new studies are being conducted in this laboratory to ascertain whether PCBs can be extracted from aquatic biota samples at lower temperatures higher fluid density without coextracting sample water.

    A method has been developed by Capangpangan et al. The technique has been modified to allow drying of small quantities 1—2 g of wet biota Hale and Gaylor, unpublished. Wet samples are applied to a glass fiber filter and suspended over a bed of calcium chloride in a closed glass container for 24 h. Assuming successful extraction of a wet sample, any water present in the extract must be removed before GC.

    Any blender made of glass should suffice for this step. During homogenization of larger fillets, it may be necessary to stop periodically and break up large chunks of tissue with a clean spatula until a powderlike sample consistency is achieved. Solvent rinsed mason jars are excellent for sample storage prior to SFE and long-term archiving. Surrogate and internal standards can be prepared from neat or by serial dilution of commercially prepared standards.

    All standards should be prepared in clean, solvent-rinsed volumetric glassware and stored in a freezer when not in use. Tape is adequate for properly labeling standards, collection vials, and so on. It is essential that working surfaces i. Failure to remove any excess material from the top rim of the vessel can lead to vessel pressurization problems, resulting in instrument error messages and system shutdown during SFE.

    Addition of large solvent volumes can lead to leaching of analytes and subsequent loss through the bottom of the extraction vessel. Transfer of the alumina to a to mL beaker after activation is a matter of convenience. The beaker permits the alumina to be poured directly into the vessel without the need for a spatula, thus minimizing the potential for contamination. Trap configuration will vary widely among instruments. In this integration, we are the JavaScript millions working fast risk Readiness and its dilemmas in segments and students abuse.

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