Analytical supercritical fluid extraction of adsorbent materials

Development of a sequential supercritical fluid extraction method for the analysis of nitrated and oxygenated derivatives of polycyclic aromatic hydrocarbons in urban aerosols

A two-step supercritical fluid extraction (SFE) method has been developed for the analysis of oxygenated and nitrated polycyclic aromatic hydrocarbons (oxy- and nitro-PAHs, respectively) present in urban aerosol samples. The proposed SFE procedure first involves an extraction step using pure CO2 in order to remove the less polar compounds from the matrix and a second consecutive step using toluene-modified CO2. The oxy- and nitro-PAHs are obtained in the second step. Parameters affecting both collection efficiencies and the selective extraction of oxy- and nitro-PAHs in the second SFE step were optimised. Analysis of the extracts was performed using gas chromatography with electron-capture detection and coupled to mass spectrometry. The proposed SFE method was compared with a conventional extraction technique such as sonication and good agreement in the results was obtained. Nevertheless, clean up of sonication extracts was needed, whereas no purification was necessary for SFE extracts. The SFE method was applied to the analysis of oxy- and nitro-PAHs in urban aerosol samples and 9-fluorenone, 9,10-anthraquinone, 2-methyl-9,10-anthraquinone, benzanthrone, benz[a]anthracene-7,12-dione and 1-nitropyrene were identified at concentrations ranging between 15 and 364 pg m(-3).

An alternative supercritical fluid extraction system for aqueous matrices and its application in pesticides residue analysis

Supercritical fluid extraction (SFE) is a rapid and convenient method for the isolation of organic compounds from environmental samples. This paper describes a supercritical carbon dioxide (CO2) extraction system that uses a newly designed extraction cell to recover organic compounds from an aqueous matrix. Analysis of the extracts by gas chromatography-electron capture detector (GC-ECD) indicated that the herbicide trifluralin (2,6-dinitro-N,N-dipropyl-4-trifluoromethylaniline) could be quantitatively extracted by using the SFE system proposed with small amounts of sample. The percentage of recovery obtained with the SFE system described was twice as high as the result obtained using a conventional solid-phase extraction technique. Extraction by SFE was completed in a short period of time using a simple and low-cost home-made system that did not require the use of organic solvents.

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 (microLC) with UV detection at 260 nm, was developed for selective determination of fenpyroximate in apple samples. The packed capillary liquid chromatography method utilises 20 microl injection volumes with on-column focusing. A 350x0.32 mm capillary column packed with Kromasil 100-C18 of 5 microm particle size was used with a mobile phase of acetonitrile-10 mM ammonium acetate (85:15, v/v) at a flow of 5 microl/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 degrees 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 microm poly(vinylidene difluoride) syringe filter before microLC analysis. Validation of the method was accomplished with apple samples spiked with fenpyroximate, covering the range of 0.1 to 1.0 microg/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.

The kinetics and reversibility of the partitioning of polychlorinated biphenyls between air and ryegrass

Lolium multiflorum (ryegrass) was contaminated with technical mixtures of polychlorinated biphenyls (PCBs) via the gas phase and the subsequent elimination of the PCBs from the vegetation was studied under field conditions. There was a pronounced decrease in the concentrations of the di- through to the pentachlorinated congeners over the 240-h elimination period. For many of the congeners the elimination was nearly complete, suggesting that the partitioning of these compounds from the gas phase into ryegrass is largely reversible. The elimination followed first order kinetics. The elimination half-lives were linearly proportional to the plant/air equilibrium partition coefficients (K(PA)) of the PCB congeners and ranged from 22 h for PCBs 8 + 5 to 87 h for PCBs 84 + 101. For the hexa- through to the octachlorinated congeners no significant decrease in the concentration of the vegetation was observed during the elimination experiment. The elimination was described well using a two-resistance model of PCB desorption which indicated that elimination of the di- and trichlorinated PCBs was limited by transport within the plant itself while elimination of the higher chlorinated congeners was limited by transport from the plant surface into the atmosphere. Furthermore, the results demonstrate that if elimination of higher chlorinated PCBs from ryegrass via biological or photochemical degradation occurs, then it is very slow.

Supercritical fluids in separation science--the dreams, the reality and the future

The last 20 years have seen an intense interest in the use of supercritical fluids in separation science. This started with the introduction of commercial instruments first for packed and then for capillary chromatography and it looked as if this would be a technique to rival gas-liquid chromatography and HPLC. The activity developed quite rapidly into packed column supercritical fluid separations then into supercritical fluid extraction. However, in recent years there has been a decline in publications. These later techniques continue to be used but are now principally applied to a limited group of applications where they offer significant advantages over alternative techniques. This review looks back over this period and analyses how these methods were developed and the fluids, detectors and applications that were examined. It suggests why many of the initial applications have vanished and why the initial apparent promise was not fulfilled. The rise and fall of supercritical fluids represents a lesson in the way analysts approach new techniques and how we might view other new separation developments at the end of this millennium. The review looks forward to the future of supercritical fluids and their role at the end of the first century of separation science. Probably the most important idea that supercritical fluids have brought to separation science is a recognition that there is unity in the separation methods and that a continuum exists from gases to liquids.