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The supercritical fluid extraction (SFE) of metal ions was assessed in terms of the ability of the process to extract, solvate, transport and collect metal species. The extraction efficiency (per cent removed from the sample matrix), collection efficiency (per cent recovered in the collection solvent) and SFE residue (unextracted metal complex or metal ion recovered from the apparatus by flushing with an organic or acidic solvent, respectively) were determined to ascertain whether a mass balance for the metal could be achieved. Using this approach, it was demonstrated that the amount of metal extracted from the sample matrix did not necessarily correspond to the concentration of metal recovered in the collection solvent, as the chelated metal complex could partially degrade and/or dissociate in the supercritical fluid prior to collection. Typically, a discrepancy of 1 to 15% could be obtained. The non-fluorinated metal β-diketones and dithiocarbamates had a greater tendency to dissociate and/or degrade in a supercritical fluid (i.e., ca. 14 and 5%, respectively) than the corresponding fluorinated metal complex (i.e., ca. 6 and 1%, respectively). As for the collection solvents, a range of suitable fluids were found to be capable of obtaining quantitative metal complex recoveries, including methanol, chloroform, isobutyl methyl ketone or 10% nitric acid. A radioactive isotope, 177Lu, was used to trace the location of the metal residue in the SFE apparatus.

Supercritical fluid extraction of cobalt ions was evaluated in terms of the ability of the process to extract, solvate, transport and to collect the metal species. The aim of the study was to ensure that a mass balance could be obtained for the metal before and after extraction with supercritical carbon dioxide (CO2). The stability of the ligand and resulting metal complex were assessed as was the synergistic effect of the presence of water in the extraction. Two widely used β-diketones, namely, acetylacetone (AcAc) and hexafluoroacetylacetone (HFAcAc) were chosen to extract spiked cobalt from the surface of stainless steel and >90% of the metal was extracted and collected using the HFAcAc ligand with supercritical CO2.

Real world samples which contain high concentrations of water and/or extractable material frequently cause intermittent or irreversible plugging of the flow control device during off-line supercritical fluid extraction (SFE). A supercritical fluid (SF) flow control/collection device has been developed which can simultaneously maintain the extraction flow-rate of the SF (±0.1 ml/min) and quantitatively (>90%) collect analytes as volatile as n-octane directly into an organic solvent. With this device, the extract is partially depressurized through a heated capillary restrictor and into a pressurized collection solvent, so that both temperature and pressure are used to maintain the solubility of the extract in the SF. The pressurized mixture is finally depressurized to atmospheric conditions using a backpressure regulator, so the extract can be recovered in the collection vial. Depending on the sample matrix, a restrictor heater temperature of 200 °C and a backpressure regulator with a heated (>5 wt% water in sample) or unheated (

Supercritical fluid extraction of metals in the presence of complexing agents for environmental monitoring, cleanup, and metals processing is now being extensively researched, and there is a need for solubility data of metal complexes. In this paper, the method used is the combination of a study of chromatographic retention over a wide range of pressures at 40, 50, 60, and 70 `C, followed by selected direct solubility measurements, to provide a comprehensive set of solubility results obtained with minimum effort. The method relies on the assumption that an inverse relationship exists between chromatographic retention and solubility in the mobile phase. This assumption is checked in this study. Results are presented for the solubility of ferrocene in supercritical carbon dioxide and a nickel complex, (5,7,12,14-tetramethyl-2,3:9,10-dibenzo[b,i][1,4,8,11]tetraazacyclotetradecine)nickel(II), in supercritical carbon dioxide modified with 10 vol % methanol.

A coupled supercritical fluid extraction-gas chromatography (SFE-GC) method has been developed for the quantitative extraction and analysis of gasoline and diesel range organics from real world environmental samples. Petroleum-contaminated samples containing gasoline- to diesel- and motor oil-range hydrocarbons (total hydrocarbon content typically ranging from 2 to 26 mgg) could be quantitatively extracted by a 15-min SFE-GC extraction using 400 atm (1 atm = 101 325 Pa), 60°C CO2. The SFE-GC hydrocarbon recoveries from real-world samples were comparable to those obtained by sonicating the samples in methylene chloride for 14 h, except for the gasoline recovery which was higher by SFE-GC analysis due to the more efficient collection of the more volatile analytes. Reproducibilities for replicate SFE-GC extractions and analyses were typically

Of 21 potential drying agents investigated, five (anhydrous and monohydrated magnesium sulfate, molecular sieves 3A and 5A and Hydromatrix) were able successfully to prevent restrictor plugging by water during off-line supercritical fluid extraction (e.g., 400 atm CO2 at 60°C) by retaining the majority of the water (but generally not the analytes of interest) in the extraction cell. Increasing the extraction temperature (e.g., to 150°C) or adding a polar modifier [10% (v/v) methanol] to the CO2 extraction fluid greatly reduced the amount of water the drying agents retained. However, when 10% (v/v) toluene was used for the extraction, the drying agents were able to retain the majority of the water (ca. 80% w/w). Polar and non-polar pollutants were quantitatively extracted from the wet drying agents (i.e., water present), but nearly all of the drying agents selectively retained at least one of the polar analytes if used dry (i.e., no water present), thus demonstrating the need for a spike recovery study to determine the potential for analyte loss. The successful drying agents eliminated restrictor plugging when used with moderately wet [ca. 20% (w/w) water at a 1:1 reagent-to-sample ratio] and very wet [ca. 90% (w/w) water at 4:1 reagent-to-sample ratio] samples without the need to heat the restrictor or the collection solvent.

Fused-silica restrictors used for off-line supercritical fluid extraction (SFE) frequently break when extractions are performed with polar supercritica

The development of quantitative supercritical fluid extraction (SFE) methods for the recovery of organic pollutants from environmental samples requires three steps: quantitative partitioning of the analytes from the sample into the extraction fluid, quantitative removal from the extraction vessel, and quantitative collection of the extracted analytes. While spike recovery studies are an excellent method to develop the final two steps, they are often not valid for determining extraction efficiencies from complex real-world samples such as soils and sediments, exchaust particulates, and sludges. SFE conditions that yield quantitative recoveries of spiked analytes may recover < 10% of the same analytes from real-world samples, because spiked pollutants are not exposed to the same active sites as the native pollutants. Because of the heterogeneous nature of environmental samples, the partitioning step may be controlled by analyte solubility in the extraction fluid, kinetic limitations, and/or the ability of the extraction fluid to interrupt matrix-analyte interactions. While the interactions that control SFE rates from heterogenous environmental samples are not well understood, a generalized scheme for developing quantitative SFE methods is proposed based on interactive considerations of the collection efficiencies after SFE, fluid flow parameters in the extraction cell, analyte solubility, extraction kinetics, and analyte-matrix-extraction fluid interactions. The proposed development scheme includes increasing SFE extraction rates by the use of more polar fluids than CO2 such as CHClF2, the addition of organic modifiers to CO 2, and the use of high temperature extractions with pure CO2. Validation of quantitative extractions based on multiple extraction methods (SFE followed by liquid solvent extractions) is also described.

The relative extraction rates of native polycyclic aromatic hydrocarbons (PAHs) ranging from naphthalene (M = 128) to benzo[b]fluoranthene (M = 252) and those of spiked deuterated PAHs (d-PAHs) from heterogeneous environmental samples including petroleum waste sludge, urban air particulate matter (SRM 1649), and railroad bed soil were compared using sequential extractions with pure supercritical CO[sub 2] or modified (10% v/v methanol) supercritical CO[sub 2] and using sonication with methylene chloride. Regardless of the spiking method (injection of the spike or suspension of the sample in the spiking solution) or aging time (up to 14 h), the extraction rates of most of the spiked d-PAHs were substantially (up to 10-fold) higher than those of the same native PAHs. Differences in extraction rates of the spiked and native PAHs were most dramatic for the lower molecular weight PAHs, indicating that relatively volatile species such as naphthalene must be tightly bound in order to remain associated with a real-world sample. In most cases, 30-min extractions with pure CO[sub 2] quantitatively recovered (>90%) the spiked deuterated-PAHs, but only extracted ca.25-80% of the native PAHs. Similar differences were observed using conventional methylene chloride sonication, demonstrating that spike recovery studies are not valid for developing quantitativemore » extraction methods for heterogeneous environmental samples. 21 refs., 8 figs., 4 tabs.« less

Supercritical carbon dioxide was used to extract the sesquiterpene lactone parthenolide, which is reported to be the active component of the medicinal herb feverfew ( Tanacetum parthenium ), from dried plant material for gas-liquid chromatographic analysis. The extracts also contained significant amounts of camphor and chrysanthenol acetate. The pressure and densities required for quantitative extraction and the methods of sample collection were studied. The addition of methanol or acetonitrile as modifiers in the carbon dioxide gave higher yields of parthenolide bu the extractions were less selective and considerable amounts of co-extractives were obtained. By employing a trapping column made of cellulose or silica the purity of the extracts could be improved and a practical method for the rapid isolation of parthenolide is described.

Real-world environmental samples which contain high concentrations of water and/or extractable matrix components frequently cause intermittent or irreversible plugging of capillary flow restrictors during off-line supercritical fluid extraction. Heating the entire restrictor at 50°C produces a constant extraction flow-rate (± 0.03 ml/min) for such samples, but poor collection efficiencies (30–65% recovery for polycyclic aromatic hydrocarbons) were obtained because the supercritical fluid could not be depressurized directly into the collection solvent. While the collection efficiency was improved (80–90%) by nebulizing an organic solvent with the restrictor effluent, a simpler method was to heat all but the last 3 cm of the restrictor and to depressurize the extract directly in the collection solvent. Depending on the sample matrix, restrictor heater temperatures ranging from 50 to 200°C were required to avoid restrictor plugging. With proper heating, constant extraction flow-rates (± 0.07 ml/min) and high collection efficiencies (90–100%) for polycyclic aromatic hydrocarbons and n -alkanes as volatile as n -octane were achieved.

Supercritical fluid extraction (SFE) recoveries for native pollutants including PCBs from a standard reference material sediment (SRM 1939), PAHs from a petroleum waste sludge, and PAHs from railroad bed soil were compared using supercritical CHCIF 2 (Freon-22), N 2 O, and CO 2 . While SFE with pure CO 2 yielded the lowest recoveries for each sample, CHCIF 2 consistently yielded the highest extraction efficiencies, most likely because of its high dipole moment

α-Cellulose has been used as a model plant matrix to investigate the conditions required to optimize the supercritical fluid extraction of typical plant constituents, limonene, caryophyllene, carvone, eugenol and santonin, using carbon dioxide as the extraction medium. The conditions required for the successful recovery of the analytes were monitored by gas-liquid chromatography. Timed recovery studies enabled differences in the rates of extraction to be determined to ensure that sufficiently long extraction runs were used. Subcritical and supercritical extractions over the ranges −10 to 80°C and 50–250 bar were examined and 250 bar and 40°C were chosen as the optimum conditions. The effects of the addition of modifiers to the supercritical fluid were also examined. The work also demonstrated that increased selectivity for polar analytes such as lactones could be obtained by trapping the extract on a silica column coupled with selective elution.

Supercritical fluid extraction (SFE) collection efficiences of 66 compounds with a wide range of volatility and polarity were examined. Good collection efficiencies required efficient partitioning of the analyte into the collection solvent after depressurization, and factors including collection solvent polarity and temperature were found to be more important than collection solvent volume and height. Heating the collection solvent with a heat gun to avoid plugging of the outlet restrictor resulted in 20−50% losses of the more volatile analytes, while > 90% trapping of all test analytes could be attained by controlling the solvent temperature at 5°C. Extraction cell geometry (“long, narrow” versus “short, broad” vessel) at constant internal volume and the orientation of the extraction cell were found to have negligible effects on the extraction rates of polycyclic aromatic hydrocarbons (PAHs) from railroad bed soil and flavor and fragrance compounds from lemon peels. The supercritical fluid flow-rate also had little effect on the extraction rate of native PAHs provided that it was sufficient to sweep the cell dead volume every ca. 3 min.

Conventional supercritical fluid extraction (SFE) system are constructed using stainless steel due to its relative inertness, ready availability, tensile strength and low cost. Recently, metal complex solubilities and metal extraction using chelating agents have been investigated using a stainless steel SFE system. Metal complexes are usually soluble in supercritical carbon dioxide (SC-CO2) and so this was the fluid of choice for the experiments. During the chelation step, temperature and pressure have great effect on the extraction efficiency. Using a metal salt as a sample, and hexafluoroacetylacetone (HFAcAc) as a ligand, the most efficient extraction conditions were found to be 60°C and 400atm. However, when contaminated soil was used as a sample, extraction efficiency fell. This was thought to be related to the corrosion of the stainless steel SFE system by the ligand HFAcAc. During the 30min extraction period, 1678μg of iron was obtained. The corrosion of the SFE system was much greater during the soil extraction than during both the metal salt extraction and metal complex solubility experiments. Copyright (C) 2000 Elsevier Science B.V.

The saying ‘time is money’ is becoming ever more common in the laboratory environment. There has always been a need to control analytical costs in terms of solvent usage and disposal, consumable expenditure and administration overheads. However, there is currently an even greater emphasis on the time an analysis takes, and this has led to the development of automated commercial extraction methods using solvent, microwave-assisted and supercritical fluid extraction (SFE) systems. To automate the analytical process fully the extraction and analysis procedures need to be combined to produce a coupled on-line technique that minimises the sample handling and preparation steps which contribute to analyte loss, degradation and/or contamination. This direct transfer of extracted analytes into the analyte separation and detection system produces a more sensitive analysis and increases the laboratory sample throughput. For example, the extraction and chromatographic analysis of real-world samples with low (ppm—ppb) analyte concentrations can be achieved within 1 h using an on-line approach [1-3].

Sample preparation is often proved the most time consuming part of a chromatographic assay because it usually involves an extraction procedure with organic solvents and the subsequent need to evaporate the solvent to concentrate the extract.

A model for dynamic supercritical fluid extraction (SFE) is proposed, which contains the steps of: rapid fluid entry into the matrix; a reversible release process such as desorption from matrix sites or penetration of a biological membrane; transport, by diffusion or otherwise to the edge of a matrix particle; and removal by biological membrane; transport, by diffusion or otherwise to the edge of matrix particle; and removal by solvation in the fluid. It can explain the following kinetic features of dynamic SFE : (i) a slow initial extraction; (ii) a more rapid extraction phase; and (iii) a slow final phase, which can be so slow that it appears that extraction is complete when only a fraction of the solute present in the matrix has been recovered. The model may be used to extract values for the parameters quantifying the individual steps, to understand further the SFE process.