A poly(amine ester) dendrimer with naphthyl units (G1N6) has been synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of G1N6 by adding each of Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Mg²⁺, Ni²⁺, and Zn²⁺ in acetonitrile solution. Large changes were observed in the fluorescence spectra of G1N6 upon the addition of Al³⁺, Cu²⁺, and Zn²⁺.

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In order to study the decontamination nature of the reactive extraction of uranium in the presence of some metal chemicals using a single-phase mixture of HNO₃, H₂O and tri-n-butylphosphate (TBP) in supercritical carbon dioxide (SC-CO₂), we measured the decontamination factors (DFs) of Sr, Zr, Mo, Ru, Pd, Ce and Nd from their mixture with U. These elements were originally added to U₃O₈ as SrO, ZrO₂, MoO₃, RuO₂, Pd, CeO₂ and Nd₂O₃, and the extraction was performed at 18 MPa and 323 K with the single-phase mixture. The DFs for these elements were determined to be greater than 10³ when the molecular ratio of U to TBP in the extracted complex was greater than 0.3. Dilution by SC-CO₂ effectively increased the DFs.

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Several investigations on the extraction of dioxins from soil and fly ash with supercritical fluid have been reported; however, few of them describe the influence of components on the extraction. We extracted dioxins from eight samples with different values of organic carbon content and surface area with supercritical CO₂ at a temperature of 463 K, a pressure of 40 MPa, and using 10% toluene as an entrainer. We researched the influence of the characteristics of soil and fly ash on supercritical CO₂ extraction of dioxins. The results revealed that the extraction efficiencies of PCDD/DFs and PCBs were high for all soil samples, while that of fly ash samples decreased with the increase in organic carbon content and surface area. The extraction efficiencies of dioxins from four standard samples, activated carbon, humic acid, alumina, and florisil, were also examined. The results revealed that the extraction efficiencies were strongly influenced by activated carbon like components present in the samples.

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The solubility of tris(pentane-2,4-dionato)chromium(III) (Cr(acac)₃) in supercritical carbon dioxide (SC-CO₂) containing organic modifiers (1,1,1,3,3,3-hexafluoro-2-propanol (HFP) and 3,5-bis(trifluoromethyl)phenol (BTMP)) of hydrogen-bond donors was investigated by UV/VIS spectrophotometry. A great solubility enhancement of Cr(acac)₃ in SC-CO₂ was accomplished by adding HFP and BTMP. The association constant of Cr(acac)₃ with HFP and BTMP in SC-CO₂ could be determined from the relationship of the solubility enhancement against the concentration of the modifier. The association constant linearly increases with an increase in the acid dissociation constant of the modifiers.

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The cross-linking structure of the ultra violet (UV)-cured resin prepared from dipentaerithritol hexacrylate (DPHA) was characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with supercritical methanolysis. The MALDI-mass spectrum of the decomposition products obtained by supercritical methanolysis contained a series of peaks of sodium-cationized methyl acrylate (MA) oligomers up to around m/z = 4000 formed through selective cleavage and methylation occurred at ester linkages in UV-cured DPHA. Furthermore, in order to observe widely distributed sequence lengths in the cross-linking junctions, the decomposed products of the cured resin were then fractionated using size exclusion chromatography followed by the MALDI-MS measurements of the individual fractions. The MALDI-mass spectra of the lower molar mass fractions mainly consisted of a series of peaks of MA oligomers around m/z values of several thousands, whereas those of higher molecular weight showed a broad peak up to m/z ca. 180000. The observed distributions of the supercritical methanolysis products suggested that the network junctions in the given UV-cured resin were composed of up to around 2000 acrylate units.

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Supercritical water (scH₂O) is utilized for organic synthesis as an acid- or a base-catalyst as well as a useful replacement for organic solvents. There have been few works on the use of scH₂O for acid- or base-catalyzed organic synthesis, because the ion product of scH₂O is much lower than liquid water under certain conditions. Our recent studies by in situ Raman and IR spectroscopic measurements were allowed to expect the occurrence of acid- or base-catalysis of scH₂O. Contrary to the conventional wisdom that acid- or base-catalyzed reactions will not take place in scH₂O, these results indicated the possibilities of scH₂O participating in Lewis acid- or base-catalysis, besides the Brønsted acid-base function. In this paper, we thus demonstrate that the new-generation syntheses of lactam, arylated olefin, and monoterpene alcohols can be successfully created in scH₂O.

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The local density around pyridazine was evaluated by examining the UV-vis spectral shift of pyridazine in a high-pressure liquid state and supercritical water from 25 to 450°C and from 20 to 45 MPa. Augmentation of the local density was observed from 380 to 420°C, and showed the maximum at a lower density than the critical density of water. The degree of hydrogen bonding was estimated in consideration of the local density augmentation. The estimated degree of hydrogen bonding under subcritical conditions without any difference between the local density and the bulk density corresponded to the previously reported results with a UV-vis absorbance spectral shift of quinoline and an NMR proton chemical shift. However, the degree of hydrogen bonding near the critical point of water was larger than that in the case that the local density augmentation was not taken into account. At 380°C and 0.2 g cm^-3 of the bulk density there are 30% as many hydrogen bonds as those under the ambient condition, and it was around 1.5-times that without considering local-density augmentation.

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The supercritical fluid extraction (SFE) method using CO₂ as a medium with an extractant of HNO₃-tri-n-butyl phosphate (TBP) complex was applied to extract uranium from several uranyl phosphate compounds and simulated uranium ores. An extraction method consisting of a static extraction process and a dynamic one was established, and the effects of the experimental conditions, such as pressure, temperature, and extraction time, on the extraction of uranium were ascertained. It was found that uranium could be efficiently extracted from both the uranyl phosphates and simulated ores by the SFE method using CO₂. It was thus demonstrated that the SFE method using CO₂ is useful as a pretreatment method for the analysis of uranium in ores.

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The binary diffusion coefficients, D₁₂, and retention factors for myristoleic acid and its methyl ester at infinite dilution were measured by the chromatographic impulse response technique in supercritical carbon dioxide at temperatures of 313.2, 333.2 and 343.2 K and pressures from 9.2 to 30 MPa for the acid, and from 8.0 to 14 MPa for the ester. Although the D₁₂ values were represented by the two correlations, the D₁₂/T vs. CO₂ viscosity and the Schmidt-number correlations, which are valid for more than 40 compounds that we have measured so far, significant temperature dependences were observed for the ester. Moreover, the D₁₂ values for the ester at 313.2 K downward deviated from the background values around 400 kg m^-3, where the partial molar volumes, obtained from the correlation between the retention factors measured and CO₂ densities, showed large negative values.

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Supercritical fluid extraction was coupled to comprehensive two-dimensional supercritical fluid chromatography with conventional packed columns. With this system, three modes of operations were feasible, such as SFE-SFC, SFC×SFC, and SFE-SFC×SFC. The operations for valve switching and data acquisition were automated using in-house software. In order to evaluate the present system, SFE-SFC for polymer additives in polypropylene, SFC×SFC for a mixture of benzene derivatives with different polarities, and SFE-SFC×SFC for styrene oligomers in polystyrene were performed. With SFE-SFC×SFC, diastereomers were resolved for linear tetramers and pentamers as well as trimers with the tetraline moiety.

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The extraction of carotenoids from Japanese persimmon peels by supercritical fluid extraction (SFE), of which the solvent was CO₂, was performed. In order to enhance the yield and selectivity of the extraction, some portion of ethanol (5 - 20 mol%) was added as an entrainer. The extraction temperature ranged from 313 to 353 K and the pressure was 30 MPa. The effect of temperature on the extraction yield of carotenoids was investigated at 10 mol% of the ethanol concentration in the extraction solvent, and a suitable temperature was found to be 333 K among the temperatures studied with respect to the carotenoid yield. With increasing the entrainer amount from 0 to 10 mol% at a constant temperature (333 K), the carotenoid yield in the extraction was improved, whereas the selectivity of the extracted carotenoids was drastically depressed. We also conducted qualitative and quantitative analyses for the carotenoid components in the extract by HPLC, and analyzed the extraction behavior of each individual carotenoid (α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein, and zeaxanthin). The selectivity of each carotenoid changed with the elapsed time and its time evolution was dependent on the carotenoid component, indicating that the location profile and the content can be important factors to understand the SFE behavior of each carotenoid in persimmon peels.

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Supercritical fluid extraction (SFE) has been evaluated as an extraction technique for the isotope-dilution quantification of polychlorinated biphenyls (PCBs) in a sediment sample. A high-resolution mass-spectrometric system equipped with a gas chromatograph was employed for the determination of seven target PCB congeners. The effect of the operation parameters on the SFE efficiency was investigated, in which the analytical values of five target PCB congeners significantly increased with increases in the extraction temperature and pressure, and that of 4,4′-dichlorobiphenyl further increased by applying static extraction. The following conditions were found to be optimal: extraction temperature, 140°C; pressure, 30 MPa; time and mode, static for 15 min then dynamic for 30 min. Under these conditions, the addition of modifiers influenced the extraction of polar compounds, but did not affect the analytical values of the PCB congeners. The optimized method was suitable for high-throughput analysis as well as for providing accurate analytical results, which were comparable to or better than the analytical results obtained by Soxhlet extraction.

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A combined solid-phase extraction (SPE)-supercritical fluid extraction (SFE) procedure was developed for the analysis of polychlorinated biphenyls (PCBs) in wastewater. The importance of cleaning and drying the filters and SPE-disks prior to eluting PCBs with SFE was studied, leading to improved recoveries for all congeners investigated. The average PCB recovery of the final procedure, at a concentration of 18 ng/L in reagent water, was 101% with relative standard deviations ranging from 1 to 5% for the different congeners. Spiked leachate to a final concentration of 4 ng/L was extracted directly after spiking, or after 24 h of spiking. An average recovery of 112% was obtained in the direct extraction of spiked leachate.

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A novel pretreatment method has been developed for determination of toxic metals in plastic materials by their decomposition under supercritical water conditions. Particularly, quantitative analysis of cadmium in polyethylene has been demonstrated using inductively coupled plasma atomic emission spectrometry combined with supercritical water treatment. All the cadmium in a polyethylene sample was obtained as an aqueous solution by the treatment with supercritical water containing 12.4% of hydrogen peroxide at 673 K. Although a complete recovery of the aqueous solution from the reactors has not yet been attained, we verified that the present method was effective and promising for quantitative analysis of trace amounts of hazardous metals in plastic materials.

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The extraction of lead from fly ash produced during the thermal treatment of municipal solid wastes was studied using supercritical carbon dioxide (SC-CO₂) and Cyanex 302 (bis(2,4,4-trimethylpentyl)monophosphinic acid). The extraction of lead from the fly ash was carried out in a 5 cm³ internal volume reaction vessel under static extraction conditions at 323 K, and 24 MPa for 1 h. The extraction efficiencies of lead ranged from 4% to the total extraction under the conditions of 0.05 g fly ash with 2 cm³ Cyanex 302. There was a linear relationship between the extraction efficiencies of lead using the SC-CO₂ + Cyanex 302 and using a water-based method described by JLT13.

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4,4′-Bis(dihexylaminocarbonyl)-2,2′-bipyridine (BDC-Bipy) was synthesized and studied systematically as a chelating reagent for metal ions extraction in supercritical CO₂. The compound showed high extraction efficiency for Co²⁺ (100%), Cu²⁺ (100%), Cd²⁺ (98.2%), and Zn²⁺ (100%) ions and good extraction efficiency for Sr²⁺ (79.4%) and Pb²⁺ (89.8%) when the extraction was performed in supercritical CO₂ at 313 K and 25 MPa with the system of BDC-Bipy, deionized water and perfluoro-1-octanesulfonic acid tetraethylammonium salt. The recoveries of mixed metal ions were also measured; unfortunately, the system of extraction has no selectivity for the metal ions.

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Compared to generally used solvent extraction methods, supercritical fluid extraction (SFE) with carbon dioxide has the advantages of automation and simple operation in preparing samples for pesticide residue analysis. This report is the outcome of our evaluation of the practicality of SFE for the preparation of samples for pesticide residue analysis. We studied the recovery of 303 compounds with several crops by a simultaneous analytical method of SFE, cartridge column purification, followed by GC/MS determination. We achieved 70 to 120% recovery for more than 80% of the examined compounds.

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