Off-line Supercritical Fluid Extraction Research Articles

Analysis of citrates and benzoates used in poly(vinyl chloride) by supercritical fluid extraction and gas chromatography

Supercritical fluid extraction (SFE) has been demonstrated to be a useful tool in the determination of additives in polymeric materials. This paper describes the determination of some citrates and benzoates in poly(vinyl chloride) blended with 33–34% of plasticizer using off-line SFE followed by gas chromatography. Experimental factors affecting SFE have been studied by gravimetric analysis, followed by analysis of the extracts using a gas chromatograph equipped with a flame ionization detector. The extraction process is governed by the solubility of the plasticizers in the supercritical fluid or by their diffusion through the polymer matrix, which depend on the pressure and temperature used. Maximum extraction (>99%) is obtained at pressures and temperatures higher than 40 MPa and 80 °C, respectively. Due to purge losses, the collection efficiency of plasticizers into a liquid solvent ranges from 85 to 90%. The applicability of the SFE method is demonstrated using real samples and comparing the results with those obtained by conventional Soxhlet extraction.

Effect of pressure, temperature and time on supercritical fluid extraction of citrate and benzoate plasticisers from poly (vinyl chloride)

Supercritical Fluid Extraction (SFE) has been demonstrated as a useful tool in the analysis of polymeric materials. This paper describes the off-line SFE followed by Gas Chromatography determination of some citrate and benzoate plasticisers used in poly (vinyl chloride) (PVC). Experimental factors affecting SFE with carbon dioxide have been studied by gravimetric analysis. Recoveries of analytes were calculated with the use of a Gas Chromatograph with a flame ionisation detector. The extraction process can be kinetically controlled by the solubility of plasticisers in the supercritical fluid or by their diffusion through the polymer depending on pressure and temperature conditions. Quantitative extractions (>99%) are obtained at 39.5 MPa, 100 °C and 20 min, while some losses in the collection of plasticisers in a liquid solvent (ranges from 85 to 95%) are observed.

Determination of fenpyroximate in apples by supercritical fluid extraction and packed capillary liquid chromatography with UV detection

A method using off-line supercritical fluid extraction (SFE) and micro liquid chromatography (μLC) with UV detection at 260 nm, was developed for selective determination of fenpyroximate in apple samples. The packed capillary liquid chromatography method utilises 20 μl injection volumes with on-column focusing. A 350×0.32 mm capillary column packed with Kromasil 100-C 18 of 5 μm particle size was used with a mobile phase of acetonitrile–10 m M ammonium acetate (85:15, v/v) at a flow of 5 μl/min. A two-step SFE procedure was used to extract fenpyroximate selectively in 2 g apple samples, with Hydromatrix (HMX) added as a water absorbent at a 1:1 (w:w) ratio. Fenpyroximate was extracted at 200 bar and 90°C for 15 min using carbon dioxide at a flow of 2 ml/min, and solvent trapping collection in 10 ml acetonitrile. The volume of the acetonitrile extract was reduced by evaporation and water was added to a final composition of acetonitrile–water (40:60, v/v). The resulting 2.0 ml solution was filtered using a 0.45 μm poly(vinylidene difluoride) syringe filter before μLC analysis. Validation of the method was accomplished with apple samples spiked with fenpyroximate, covering the range of 0.1 to 1.0 μg/kg. The within-day and between-day repeatabilities were in the range 4–18% relative standard deviation. Accuracy, measured as recovery, was found to be approximately 60%. Apple samples from a field treated with fenpyroximate were analysed. None of the samples contained fenpyroximate above the quantification level.

Supercritical fluid extraction/γ-radiolysis of PCBs from contaminated soil

Off-line supercritical fluid extraction (SFE) followed by γ-radiolysis as an alternative treatment technique for PCB-contaminated soil was investigated in this study using BZ #54 (2,2′,6,6′-tetrachlorobiphenyl) as the model compound. The preliminary results indicate that removal of BZ #54 from spiked sand and soil using SFE at 150°C and 20 MPa is 98% and 93%, respectively. The reduction efficiency of 864 mg/l BZ #54 in isooctane by γ-radiolysis is 99.8% at an absorbed dose of 500 kGy.

Analysis of atmospheric semi-volatile organic pollutants by adsorptiveenrichment and off-line supercritical fluid extraction—Gas chromatography

Methods have been developed for determination of semivolatile organic pollutants in air. Extraction efficiencies for test compounds are >83%, and rsd’s are <3.4% (n=3). Atmospheric samples were collected from a variety of sites in Lanzhou, China by an adsorptive enrichment method. Over 50 organic pollutants were extracted by SFE with CO2 modified with methanol. Extracts were subjected to GC and GC-MS analysis. The results showed that one of the most serious polluted regions was an oil refinery, in which total concentration of pollutants amounted to 285.75 μg·m−3. The relationships between the total concentration of pollutants and sampling time and weather were also investigated. Results showed that pollution on sunny days is more serious than that on rainy days, while pollution is most serious during the evening.

Analyte Collection in Off-Line Supercritical Fluid Extraction

A new analyte collection method for off-line supercritical fluid extraction (SFE), based on mixing of expanding supercritical effluent with overheated organic solvent vapor, is described. The mixing process takes place in a fused-silica capillary (i.d. < 500 μm). The model, describing the trapping mechanism, is validated by the collection of n-alkanes into n-hexane. Spike experiments were performed with selected PAHs (acenaphthene, fluorene, phenanthrene, pyrene, and chrysene) and with the mixture of acetophenone, N,N-dimethylaniline, and naphthalene. In the case of PAHs, from 12 common organic solvents used, quantitative recoveries (>90%) were achieved for 10 of them, the exceptions being cyclohexane and diethyl ether. The minimum solvent flow rates were found to be in the 25 (ethanol)−90 μL/min (acetone) range. Recoveries of acetophenone, N,N-dimethylaniline, and naphthalene were found to be quantitative to a CO2 flow rate of 420 mL/min (a.c.) at a 70 μL/min toluene flow rate into the collection device. In comparison with existing collection methods, the total solvent consumption was considerably reduced, and resulting extracts were concentrated more than 10 times without preconcentration. There is not a problem of analyte stripping by gaseous CO2 from the collection vial. Due to the efficient heating of the restrictor end (∼150 °C), no restrictor plugging was observed.

Restrictor plugging in off-line supercritical fluid extraction of environmental samples: Microscopic, chemical, and spectroscopic evaluations

Irreversible restrictor plugging is often a problem in supercritical fluid extraction (SFE) with linear restrictors. Restrictor plugging occurs when high temperature (200°C) off-line SFE is performed on either the marine sediment (SRM 1941) or the urban dust (SRM 1649) standard reference material (SRM). Microscopic evaluation of the linear restrictors (50 μm i.d.×40 cm long fused silica capillary) showed that a solid mass approximately 1 cm to 3 cm from the tip of the restrictor caused the plugging in the case of SRM 1941. Three distinct zones of analyte deposition were observed in the restrictor used during SFE of SRM 1649 — a thin, diffuse, granular film (3 cm to 13 cm from tip), a thick, wavy film (13 cm to 17 cm from tip), and plugs of highly viscous liquid (17 cm to 28 cm from tip). Raman microscopy and X-ray microanalysis confirmed that inorganic sulfur was the major component of the material plugging the restrictor when SRM 1941 was extracted. X-ray microanalysis and direct insertion probe mass spectrometry confirmed that dichlorophen, phthalate esters, hydrocarbon fragments, and other compounds were contained in the material plugging the restrictor when SRM 1649 was extracted. In both cases the plugging did not occur at the tip of the restrictor. Both isenthalpic and isentropic explanations for plugging in SRM 1649 and 1941 are invalid because the zones of plugging are significantly removed from the tip of the restrictor and decompression occurred over a large region of the restrictor. The analytes appeared to have condensed in the linear restrictor either immediately after exiting the oven (SRM 1649) or further down the restrictor (SRM 1941).

Supercritical fluid extraction of water samples containing ultratrace amounts of organic micropollutants

. Abstract: A true solventless off-line supercritical fluid extraction SFE method has been developed, which does not use organic solvents for trapping and for washing out of analytes. Determination of polynuclear aromatic hydrocarbons, chlorinated pesticides, and polychlorinated biphenyls in aqueous solutions based on their direct SFE extraction and on off-line solventless SFErgas chromatography coupling has been done. This new method has a detection limit at the parts per billionrparts per trillion level. For the ultralow concentration level of 0.1)1 ppt, direct SFE from water was more accurate, faster, and more reproducible than conventional sample preparation methods based on micro-liquidrliquid extraction and solid-phase extraction. Q 1999 John Wiley & Sons, Inc. J Micro Sep 11: 729)736, 1999

Determination of pesticides in high-water-content samples by off-line supercritical fluid extraction–gas chromatography–electron-capture detection

The optimization of supercritical fluid extraction of several organochlorine and organophosphorus pesticides is presented. The optimized method is compared with the classical sonication coupled to gel permeation chromatography as a clean-up method. The SFE method has been tested for 11 pesticides in spiked strawberries. At a spiking level of 100 ng/g, the pesticide recoveries were higher than 80%. The influence of the water content present in the sample is discussed. Two different approaches to solve this problem, which involve the use of anhydrous sodium sulfate mixed with the sample and alternatively the lyophilization, are presented too.

Interlaboratory evaluation of an off-line supercritical fluid extraction and gas chromatography with atomic emission detection method for the determination of organotin compounds in soil and sediments

A collaborative study was conducted, with eight laboratories participating, to determine the method accuracy and precision of an off-line supercritical fluid extraction (SFE) method for organotin compounds. This method involves extraction of organotin compounds from solid matrixes with supercritical carbon dioxide, modified with 5% methanol, at 450 atm and 60°C for 20 min in the static mode followed by 30 min in the dynamic mode. The extracted material was collected in either methylene chloride or on a C 18-bonded silica trap followed by a methylene chloride rinse. The extracted material was derivatized with pentyl magnesium bromide and analyzed by gas chromatography with atomic emission detection (GC-AED). The study design was based on the AOAC blind-replicate design with balanced replicates. The study samples consisted of three solid matrixes that were spiked with organotin compounds at 1000 ng/g (as Sn) and one unspiked matrix that contained dibutyltin and tributyltin compounds at independently determined levels. The results of this interlaboratory study indicate that the SFE method works satisfactorily for the tri- and tetra-substituted organotin compounds but that the di-and mono-substituted organotin compounds are quite difficult to extract under these conditions. Higher pressures and different modifiers may be required to enable extraction of the mono- and di-substituted organotin compounds from soils and sediments.

Optimisation of supercritical fluid extraction of polynuclear aromatic hydrocarbons from spiked soil and marine sediment standard reference material

For the determination of 16 PAHs in soils and sediment samples by GC/FID and GC/MS, the dynamic off-line supercritical fluid extraction with both pure and modified carbon dioxide has been evaluated. The optimisation of extraction parameters was performed for four individual groups of PAHs according to their number of aromatic rings (2–3 rings, 4 rings, 5 rings and 6 rings) by varying pressure (200–510 bar), temperature (50–150 °C), extraction fluid volume (10–50 ml), and the methanol modifier concentration (0–10%). Using a five level spherical factorial experimental design the number of experiments required for optimisation was 45. In spiked soil samples extraction efficiencies of 80–100% were achieved for the individual groups of PAHs. At the optimal set of conditions 10–30% lower recoveries of PAHs were obtained for the standard reference material NIST SRM 1941a (marine sediment). The largest differences between extraction recoveries of native and spiked PAHs occurred at high molecular weight PAHs. Using SFE efficiency data for the standard reference material, cluster analysis proved that dividing the 16 PAHs into four groups according to their number of aromatic rings was appropriate and correct.

Determination of Chlorinated Hydrocarbons in Marine Sediments at the Part-per-Trillion Level with Supercritical Fluid Extraction

An off-line supercritical fluid extraction method has been developed for the determination of polychlorinated biphenyls and organochlorine pesticides at the part-per-trillion level in marine sediments. Four different extraction conditions were evaluated: pure carbon dioxide at 60 °C/220 atm and 100 °C/350 atm; addition of methanol prior to the static extraction at 80 °C/350 atm; addition of methanol prior to the static extraction step and continuously during the dynamic extraction step at 80 °C/350 atm. Only the latter condition gave extraction recoveries that were comparable and for some compounds higher than Soxhlet recoveries. The significance of differences between the two extraction methodes was determined in an F- and t-test. The method was validated by analysis of a reference material from an international intercomparison exercise.

Determination of Antifungals in Rodent Diet by Supercritical Fluid Extraction Followed by Packed Column Supercritical Fluid Chromatography with Ultraviolet Detection

Supercritical fluid extraction (SFE) followed by packed column supercritical fluid chromatography with ultraviolet detection was evaluated as a quantitative method for determining 4 antifungals (fluconazole, tioconazole, hexaconazole, and UK-47,265) in rodent diet. Chromatography was achieved with a cyano-bonded silica column, UV detection at 210 nm, and methanol-modified supercritical carbon dioxide as mobile phase. The effects of modifier concentration, temperature, and column pressure on antifungal retention time was studied. Off-line SFE was optimized at 2 spike levels, ranging from 0.5 to 10 g/kg, for each of the 4 antifungals. Average recoveries ranged from 79.0% for UK-47,265 to 96.5% for hexaconazole. Overall, the procedure provides a suitable method for analyzing antifungals in spiked rodent diet.

Variable flow control and collection device for use with supercritical fluids

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 (<5 wt% water in sample) exit tube is required to eliminate restrictor plugging. By varying the pressure of the collection solvent, a range of reversible and reproducible flow-rates were obtained at both high (400 bar, 3.5 to 0.2 ml/min liquid CO 2) and low (100 bar, 0.8 to 0.1 ml/min CO 2) SFE pressures using a 50 μm I.D. capillary restrictor. At low (0.2 ml/min) SF flow-rates the solubility of several metal complexes (e.g., ferrocene and Ni[C 22H 22N 4] complex) was measured and reproducible solubility values and flow-rates (R.S.D.<8%) were obtained.

Analysis of extracts fromcedrela toona (meliaceae) by on-line and off-line supercritical fluid extraction-capillary gas chromatography

A quantitative comparison between off-line supercritical fluid extraction (SFE) and a classical solvent extraction of a limonoid compound is discussed. A two-level three factor factorial analysis was used to optimize the variables, pressure, temperature, and the length of extraction time. By a statistical analysis of variance on the preliminary data collected, pressure and temperature were the significant variables influencing the yields of the limonoid cedrelone from the ground wood of Cedrela toona (Meliaceae). The cedrelone in the extracts was analyzed by capillary gas chromatography with flame ionization and mass spectrometric detection. On-line combination of micro-SFE with gas chromatography (SFE-GC) was also performed on the wood and bark to show the applicability of the technique in the analysis of semi-volatile components in natural products. Results for on-line and off-line SFE-GC were comparable and indicated that the on-line studies could be used to predict results obtainable from large scale SFE. © 1996 John Wiley & Sons, Inc.

Supercritical fluid extraction-liquid chromatography method development for a polymeric controlled-release drug formulation

We have recently been involved in the development of a method for assaying the active component in a controlled-release drug formulation, which is composed of a drug substance covalently bonded to polymer matrix. The drug substance in the formulation is the active enantiomer of misoprostol, a synthetic analog of natural prostaglandins and the active ingredient in Cytotec ®. Our method development consisted of a systematic evaluation of dynamic, off-line supercritical fluid extraction (SFE) as sample preparation for the formulation assay. Extracts were analyzed with normal phase and reversed-phase HPLC methods. The reversed-phase system utilized postcolumn reaction to provide selective detection of the extracted prostaglandin sample components. Several SFE parameters were investigated to optimize the recovery of the drug substance from the formulation, including sample quantity, extraction cell volume, extraction duration, supercritical carbon dioxide modifier, temperature, pressure, and collection solvent. The SFE experiments were completed with a commercially available multicell extractor. Preliminary validation studies utilized a formulation made with radiolabeled drug to determine the recovery achieved under the optimized SFE conditions and assessed the precision of replicate determinations. Analysis was completed under the optimized conditions to quantitate levels of the active component and related compounds in lots of the experimental polymeric formulation and to determine the total weight per cent extracted.

Studies on trapping efficiencies of various collection devices for off-line supercritical fluid extraction

Abstract Analyte collection in supercritical fluid extraction can be difficult, especially for relatively volatile substances. Losses of polycyclic aromatic hydrocarbons (PAHs) of up to 30% are observed with different liquid collection devices. A solid-liquid trap can minimize these trapping problems. Silica gel and two different octadecylsilanes were tested as solid sorbents. Good recoveries were found with pure carbon dioxide as the extraction fluid. Higher flow-rates did not increase analyte losses. The analytes were trapped on the solid surface. The use of modified carbon dioxide was also no problem. The analytes were eluted from the solid matrix after extraction by the modifier in the liquid phase. In the extraction of PAHs from real samples, further clean-up may be unnecessary when silica gel is used as a solid trapping material.

Extraction of pesticides using supercritical trifluoromethane and carbon dioxide

The off-line supercritical fluid extraction of pesticides using trifluoromethane (CHF 3) and carbon dioxide (CO 2) is described. Pesticides containing nitrogen or phosphorus heteroatoms were used as analytes to determine the extraction ability of CHF 3 in comparison with CO 2 at various pressures and densities. A 15% increase in extraction efficiency was obtained when CHF 3 was used as the extraction solvent rather than CO 2. No selectivity was observed for different groups of pesticides, although CHF 3 has a dipole moment whereas CO 2 does not. Because in environmental matrices the hydrocarbons are mostly present in high excess compared with the pesticides, extractions were carried out without and with addition of alkanes and polycyclic aromatic hydrocarbons (PAHs). The extraction efficiency of the pesticides with CHF 3 performed without addition of alkanes and PAHs was significantly decreased.

Off-Line SFE of Bis(2-ethylhexyl) Phthalate from PVC Materials

Off-line supercritical fluid extraction with pure CO2 was used to isolate and quantify bis(2-ethylhexyl) phthalate (DIOP) from PVC samples. Two modes of analyte trapping, onto an inner solid surface of a fused silica capillary (i.d. 0.5 mm) and direct bubbling through a bulk liquid (2-propanol), have been compared. Collected samples were analyzed by high performance liquid chromatography with UV detection. Quantitative recovery of over 95% was obtained in spite of limited operating parameters of home-made SFE device (maximum of pressure 30 MPa and of temperature 70 °C) for samples containing 10 or less wt.% of DIOP.

Solute collection after off-line supercritical fluid extraction into a moving liquid layer

A solute collection method after off-line supercritical fluid extraction using a moving layer of liquid organic solvent flowing down through a fused-silica capillary (0.5 mm I.D.) is proposed. Recoveries of over 90% were measured for selected polycyclic aromatic hydrocarbons (acenaphthene, phenanthrene, fluoranthene, pyrene and benzo[a]pyrene) and s-triazine herbicides when methanol was used as a trapping solvent.