Combined supercritical fluid extraction/solid-phase extraction with octadecylsilane cartridges as a sample preparation technique for the ultratrace analysis of a drug metabolite in plasma.

Supercritical fluid extraction was coupled with solid-phase extraction using octadecylsilane cartridges for the selective isolation of ultratrace levels of a drug metabolite, mebeverine alcohol, from plasma. Plasma was directly applied to the extraction cartridge, the cartridge was washed to remove protein and then extracted under supercritical conditions using CO2/5% methanol. The effluent from the extraction cell was bubbled through a small volume of 2-propanol to trap the extracted mebeverine alcohol. The effects of extraction pressure and temperature on analyte recovery were examined. The absolute recovery, selectivity, precision, and accuracy of the combined supercritical fluid extraction/solid-phase extraction approach were compared to those of conventional solid-phase extraction using gas chromatography/mass spectrometry in the selected-ion monitoring mode. Mebeverine alcohol was used as a model compound, and dog plasma was employed as the biological matrix for these studies.     

SFE plus C18 lipid cleanup method for selective extraction and GC/MS quantitation of polycyclic aromatic hydrocarbons in biological tissues

Lipid material represents a potential interference for determination of nonpolar compounds (e.g., polycyclic aromatic hydrocarbons) in biological tissue samples. This study reports the development of a selective extraction method using supercritical CO2 that allows the GC/MS quantitation of PAHs in the presence of a substantial lipid background. Selective extraction of PAHs relies upon addition of C18 adsorbent beads to the initial sample slurry. The dried mixture, including C18 adsorbent, is placed in the supercritical fluid extraction (SFE) chamber. During the SFE process, lipids are preferentially retained on the C18 beads. This "SFE plus C18" procedure was developed by first optimizing SFE conditions (100 degrees C, 350 bar) for recovery of PAH standards. PAHs containing added model lipid compounds (stearic acid and cholesterol) were then subjected to SFE plus C18 treatment followed by GC/MS analysis. Using this approach, a recovery of 94-100% of PAHs was obtained while only 9-17% of the lipid material present was coextracted from the same test sample. The developed method is demonstrated to permit efficient recovery and detection of PAHs spiked into crab tissue, a matrix with a high lipid content.     

Analysis of cocaine, benzoylecgonine, codeine, and morphine in hair by supercritical fluid extraction with carbon dioxide modified with methanol

Supercritical fluid extraction (SFE) using CO2 modified with methanol (10%) was employed for the extraction of cocaine from human hair. Extraction conditions were developed by using designed experiments to characterize the effects of pressure, temperature, and percent methanol on the recovery of cocaine from hair. When compared to the conventional acid hydrolysis method for hair analysis, SFE was faster and gave higher recoveries. Amounts of cocaine, benzoylecgonine (cocaine metabolite), codeine, and morphine in a hair standard reference material were determined by SFE-gas chromatography/ mass spectrometry (GC/MS) and found to be in agreement with reported levels. Analyses of hair from forensic case studies are also reported.     

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 the quaternary ammonium surfactant ditallowdimethylammonium in digested sludges and marine sediments by supercritical fluid extraction and liquid chromatography with postcolumn ion-pair formation

To study the phasing-out of the quaternary ammonium surfactant ditallowdimethylammonium cation (DTDMAC), concentrations of the cation in anaerobically stabilized sewage sludges were determined before and after its replacement by better degradable compounds. DTDMAC was quantitatively extracted from digested sludges using 380 atm of supercritical CO(2) modified with 30% methanol at 100 °C. Determination of DTDMAC was performed by normal-phase HPLC with postcolumn ion-pair formation and extraction with no sample cleanup. Mean concentrations of DTDMAC in sludges from five different municipal sewage treatment plants in Switzerland decreased from 3.67 g/kg (in 1991) to 0.96, 0.47, and 0.21 g/kg of dry sludge in 1992, 1993, and 1994, respectively. The precision of the method in digested sludge for 0.1-6.0 g/kg of dry matter, as indicated by the relative standard deviation, was typically 7%. The influence of the sample matrix was studied by performing supercritical fluid extraction (SFE) in coastal marine sediments. While SFE and a conventional liquid extraction method gave equal DTDMAC concentrations in sludges, the extraction of marine sediment samples yielded 30-40% higher DTDMAC values for SFE compared to those obtained by liquid extraction. The 94% drop in DTDMAC concentrations in digested sludges is due to the replacement of this substance and is a clear result of the producers' voluntary ban on its use in Europe.     

Solubility parameters and solubilities of metal dithiocarbamates in supercritical carbon dioxide

The solubilities of Cu, Hg, and Zn complexes with seven different dithiocarbamate ligands in supercritical fluid CO(2) at 60 °C and two pressures (100 and 230 atm) are reported. In each metal chelate system, the solubility of the metal-dithiocarbamate complex shows a strong correlation with the solubility parameters of the ligands, calculated using a group contribution method. Dithiocarbamate ligands with smaller solubility parameter values form metal complexes with higher solubilities in supercritical CO(2). The solubility parameter value may provide a general guideline for selecting effective ligands for metal extraction in supercritical CO(2).     

Molecular Baskets in Supercritical CO(2)

Calixarenes are synthetic macrocyclic compounds, described as "molecular baskets" as they possess high ionophoric selectivity and form inclusion complexes with many important ionic guests. In our initial work, hexameric and tetrameric tert-butylcalixarenes, unfunctionalized at the lower rim, are shown to be separable on a diol column using supercritical fluid chromatography with methanol/chloroform-modified CO(2) as mobile phase. The variation in capacity factors for these calixarenes was studied as a function of modifier composition. However, the solubility of these molecular baskets in unmodified supercritical CO(2) is enhanced by fluorination at the upper rim. For example, when p-allylcalix[4]arene is derivatized by a thiol-ene addition reaction with heptadecafluorodecanethiol, CF(3)(CF(2))(7)(CH(2))(2)SH, a solubility of >0.12 mol L(-)(1) in supercritical CO(2) is measured for the p-heptadecafluorodecylthio-n-propylcalix[4]arene at 60 °C and 200 atm. However, subsequent lower rim functionalization to form the tetrahydroxamate derivative, while reducing the solubility, allows supercritical fluid extraction of Fe(III) by the fluorinated calix[4]arene ligands to be studied as a function of temperature and pressure and monitored using UV/visible and atomic absorption spectrometry. In particular, the visible absorption spectra obtained for the extracted Fe(III)-calix[4]arene tetrahydroxamate complex, collected in dimethyl sulfoxide, are indicative of octahedral Fe(III) complexation in a manner similar to that displayed by water-soluble siderophores. Studies on the efficiency and selectivity of Fe(III) extraction are also reported.     

Direct on-line continuous supercritical fluid extraction and HPLC of aqueous pyrethrins solutions

A new method, employing supercritical fluid extraction (SFE) connected on-line with high-performance liquid chromatography, was developed for the determination of pyrethrins and piperonyl butoxide in aqueous solutions. The principle of the laboratory-made device for SFE is based on the low mutual solubility of water and supercritical (liquid) CO2. This device works in continuous mode that offers extraction of unlimited sample volumes. Different extraction temperatures and pressures were tested to find optimum extraction conditions. The addition of organic modifier and inorganic salt to the water sample to increase extraction recovery was investigated. The method was evaluated, and it was applied for the extraction of aqueous samples spiked with commercial insecticides. The working concentration range of the method was from the limit of quantification (0.1 microg L(-1)) to the solubility of the analytes in water.     

Quantitative enzyme-linked immunosorbent assay for determination of polychlorinated biphenyls in environmental soil and sediment samples

An enzyme-linked immunosorbent assay (ELISA) for the quantitative determination of Aroclors 1242, 1248, 1254, and 1260 in soil and sediments was developed and its performance compared with that of gas chromatography (GC). The detection limits for Aroclors 1242 and 1248 in soil are 10.5 and 9 ng/g, respectively. The assay linear dynamic range is 50-1333 ng/g. Cross-reactivity of the assay with 37 structurally related potential cocontaminants in environmental soil samples was examined; none of the chlorinated anisoles, benzenes, or phenols exhibited >3% cross-reactivity, with <0.1% cross-reactivity being the norm. Soil spike recoveries of 107% and 104% were obtained for Aroclors 1242 and 1248, respectively, for a spike level of 5 mg/kg, with corresponding relative standard deviations of 14% and 17%. One hundred forty-eight environmental soil, sediment, and paper pulp samples, obtained from two EPA listed Superfund sites, were analyzed by ELISA and standard GC methods. Samples were extracted for ELISA analysis by shaking with methanol. Additional extractions of the same samples were performed either with supercritical carbon dioxide or by Soxhlet extraction with methanol. ELISA results for both the supercritical fluid and the Soxhlet extracts were in close agreement with the GC results, while the ELISA results for the methanol shake extracts were not. The data for the environmental samples demonstrated the capability of the ELISA to provide accurate results and reinforced the dependence of any detection method, including ELISA, on appropriate extraction procedures.     

超临界流体对碳纤维/环氧树脂复合材料的降解作用

为对比分析不同超临界流体对碳纤维/环氧树脂（CF/EP）复合材料的降解效果,首先,在间歇反应釜中通过超临界流体降解CF/EP复合材料,分析了不同反应温度下超临界CO₂和超临界醇对CF/EP复合材料的降解能力,并提出了降解CF/EP复合材料的超临界流体选择方法;然后,采用单丝拉伸测试、SEM以及原子力显微镜等测试手段分析了超临界正丙醇和超临界正丁醇回收碳纤维的力学性能和微观形貌。结果表明:超临界CO₂对CF/EP复合材料的降解能力较弱,正丙醇作为夹带剂时,降解效果有显著提高;超临界正丁醇对CF/EP复合材料的降解能力最强,其次为超临界正丙醇,超临界甲醇的降解能力最弱;选用的反应介质介电常数越小、偶极矩越大、溶解度参数与树脂基体越为接近,在超临界状态下CF/EP复合材料越容易降解。使用超临界流体降解CF/EP复合材料可以得到性能优异的碳纤维,与原始碳纤维相比,通过超临界正丙醇和超临界正丁醇回收的碳纤维单丝拉伸强度保持率在98%以上,且韦氏模数相近。      

Removal of gallium (III) ions from acidic aqueous solution by supercritical carbon dioxide extraction in the green separation process

Supercritical carbon dioxide extraction, which is a feasible "green" alternative, was applied in this study as a sample pretreatment step for the removal of gallium (III) ions from acidic aqueous solution. The effect of various process parameters, including various chelating agents, extraction pressure and temperature, dimensionless CO(2) volume, the concentration of the chelating agent, and the pH of the solution, governing the efficiency and throughput of the procedure were systematically investigated. The performance of the various chelating agents from different studies indicated that the extraction efficiency of supercritical CO(2) was in the order: thiopyridine (PySH)>thenoyltrifluoroacetone (TTAH)>acetylacetone (AcAcH). The optimal extraction pressure and temperature for the supercritical CO(2) extraction of gallium (III) with chelating agent PySH were found to be 70 degrees C and 3000psi, respectively. The optimum concentration of the chelating agent was found to be 50ppm. A value of 7.5 was selected as the optimum dimensionless CO(2) volume. The optimum pH of the solution for supercritical CO(2) extraction should fall in the range of 2.0-3.0.     

Effect of various chelating agents on supercritical carbon dioxide extraction of indium(III) ions from acidic aqueous solution

Indium and its compounds have numerous industrial applications in the manufacture of liquid crystal displays and semiconductors. Indium compounds are considered hazardous materials that can be carcinogenic. Supercritical fluid extraction using carbon dioxide was utilized in this research as a sample pretreatment step for extraction of indium(III) ions from the synthetic etching wastewater of the semiconductor and optoelectronic industries. Several parameters, including various chelating agents, pH of solution, molar ratio of chelating agent to indium(III) ions, temperature and pressure were systematically investigated. Indium(III) ions were extracted by supercritical CO2 combined with several various types of chelating agents including beta-diketone (AcAcH), fluorinated beta-diketone (TTAH), thiopyridine (PySH), and piperidinyldithiocarbamic acid (NCS2H) to extract the ions from acidic aqueous solution. The performance of the various chelating agents from different studies indicated that the extraction efficiency by the supercritical CO2 was in the order: NCS2H>or==PySH>TTAH>AcAcH. The optimum pH for supercritical CO2 extraction should fall in the range from 2.0 to 3.0. The optimum molar ratio of chelating agents to indium(III) ions was found to be a ratio of 10:1. It was also revealed that the optimal extraction pressure and temperature for the supercritical CO2 extraction of indium(III) with various chelating agents AcAcH, PySH and NCS2H were 70 degrees C 2000 psi, 60 degrees C 2000 psi, and 60 degrees C 2000 psi, respectively.     

Supercritical carbon dioxide extraction of 2,4-dichlorophenol from food crop tissues.

Supercritical fluid extraction with carbon dioxide has been found to be effective for the isolation of residue levels (0.1-1 ppm) of 2,4-dichlorophenol from selected plant tissues. The 2,4-dichlorophenol residues were incompletely extracted with supercritical CO2 alone, since a substantial fraction of the 2,4-dichlorophenol was covalently attached to the plant matrix. An acid pretreatment procedure was developed to partially hydrolyze the plant tissue prior to extraction, releasing the bound 2,4-dichlorophenol residues. Steam distillation showed higher residue levels for field-treated straw samples. This is attributed to the greater degree of hydrolysis inherent in the steam distillation procedure. Supercritical CO2 extraction of field-treated seed samples showed higher levels of 2,4-dichlorophenol residues than did steam distillation. The supercritical fluid extractant was able to solvate 2,4-dichlorophenol residues in the interior of the seed and transport them to the surface for collection. The aqueous medium used in steam distillation was unable to penetrate the hydrophobic seed matrix to the same degree. While the actual extraction time experienced in supercritical fluid extraction was far less than that of steam distillation (45 min vs 6 h, respectively), the total sample preparation time was similar in both methods.     

Partition coefficients of environmentally important phenols in a supercritical carbon dioxide-water system from cocurrent extraction without analysis of the compressible phase

Partition coefficients of phenol, salicylic acid, and several environmentally important chloro- and nitrophenols in a supercritical CO2-water system were measured using direct cocurrent extraction of aqueous solutions of the individual solutes with CO2. Partitioning data on the nitrophenols and salicylic acid were obtained for the first time. To bypass the troublesome and error-prone analysis of the CO2-rich phase, the present method employed only the solute concentrations in the aqueous phase before and after extraction to determine the partition coefficient. Unlike most previous engineering studies of phenol partitioning in a CO2-water system, the concentrations of phenolic solutes approached infinite dilution in both phases. This makes the results relevant to analytical-scale SFE of environmental water samples with CO2. Because of effective infinite dilution of the solutes, the partition coefficients provide a direct measure of relative CO2-philicity/hydrophilicity of the individual phenols. Compared to the octanol-water partition coefficients of substituted phenols, the CO2-water partition coefficients are more sensitive to substitution in the position neighboring the hydroxyl group.     

Voltammetric measurement in supercritical CO2 utilizing a water-in-CO2 microemulsion

A novel method for voltammetric measurement in supercritical CO2 is described. In this method a water-in-supercritical CO2 microemulsion is utilized to raise the conductivity of the fluid phase. Well-defined voltammograms for the redox reactions of ferrocene and tetramethyl-p-phenylenediamine were obtained in supercritical CO2 in the presence of the microemulsion. The electrolysis product is stabilized in the water core of the microemulsion. This implies a wide range of electrochemical synthesis involving ionic or radical species in supercritical CO2 may be possible utilizing the microemulsion. The electrochemical results obtained from the water-in-supercritical CO2 microemulsion system are different from that obtained from a supercritical CO2-ethanol mixture system.     

Micronization of dihydroartemisinin by rapid expansion of supercritical solutions

The purpose of this study was to prepare fine particles of antimalarial drug dihydroartemisinin (DHA) by rapid expansion of supercritical solutions (RESS) using carbon dioxide as supercritical fluid. The mechanical grinding by jet mill and additional vibration rod mill also was performed as a comparative method. In the RESS process, drug particles were prepared by varying processing conditions, including extraction condition, pre-expansion condition, nozzle diameter, nozzle temperature, and collecting distance. Particle size and morphology and physicochemical characteristics of the drug particles were investigated. The RESS process could produce the smaller drug particles (about 1-2 microm) when compared to mechanical grinding method (about 7 microm). All RESS processing parameters had an effect on size and morphology of drug particles. The particle size of drug was related to the solubility of drug in supercritical CO(2) at each processing condition. The fine particles of DHA (about 1 microm) with narrow size distribution could be obtained at extraction pressure of 18 MPa and extraction temperature of 32 degrees C, which was closed to the critical temperature of supercritical CO(2) whereas broad size distribution was obtained at extraction temperature of 60 degrees C. Powder X-ray diffraction study indicated that the RESS-processed particles were in crystalline form. The results revealed that RESS process is applicable for micronization of DHA.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone modified acrylic acid copolymer in supercritical fluids and its application in dental glass-ionomer cements

Compressed fluids such as supercritical CO(2) offer marvellous opportunities for the synthesis of polymers, particularly in applications in medicine and dentistry. It has several advantages in comparison to conventional polymerisation solvents, such as enhanced kinetics and simplified solvent removal process. In this study, poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone) (PAA-IA-NVP), a modified glass-ionomer polymer, was synthesised in supercritical CO(2) (sc-CO(2)) and methanol as a co-solvent. The synthesised polymer was characterized by (1)H-NMR, Raman and FT-IR spectroscopy and viscometry. The molecular weight of the final product was also measured using static light scattering method. The synthesised polymers were subsequently used in several glass ionomer cement formulations (Fuji II commercial GIC) in which mechanical strength (compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural strength (BFS)) and handling properties (working and setting time) of the resulting cements were evaluated. The polymerisation reaction in sc-CO(2)/methanol was significantly faster than the corresponding polymerisation reaction in water and the purification procedures were simpler for the former. Furthermore, glass ionomer cement samples made from the terpolymer prepared in sc-CO(2)/methanol exhibited higher CS and DTS and comparable BFS compared to the same polymer synthesised in water. The working properties of glass ionomer formulations made in sc-CO(2)/methanol were comparable and in selected cases better than the values of those made from polymers synthesised in water.     

蓝甘菊超临界萃取物成分分析及其在卷烟加香中的应用

采用超临界CO2萃取蓝甘菊,对提取物进行GC/MS成分分析,并进行卷烟加香试验。结果表明:蓝甘菊萃取物鉴定出113种成分,萃取产率0.27%。113种成分中,相对百分含量最高的是红没药醇氧化物(50.303%)、β-金合欢烯(19.530%);萃取物稀释至1%后在卷烟加香试验中使用0.05%~0.20%效果较好,能明显改善香气质感,丰富卷烟香气。     

Na(4)EDTA-Assisted Sub-/Supercritical Fluid Extraction Procedure for Quantitative Recovery of Polar Analytes in Soil

Supercritical carbon dioxide (SC-CO(2)) is effective in extracting nonpolar and slightly polar chemicals from soils. However, pure SC-CO(2) is unsatisfactory for recovering polar chemicals in soils. A simple supercritical fluid extraction (SFE) procedure was developed to quantitatively recover polar and nonpolar chemicals from soils. The polar chemicals tested were aromatic acids and phenols. The nonpolar and slightly polar chemicals used as model compounds were common pesticides and environmental pollutants such as polycyclic aromatic hydrocarbons. The procedure required pretreatment of the samples with 15% water (g/g), 5% (ethylenedinitrilo)tetraacetic acid tetrasodium salt (Na(4)EDTA) (g/g), and 50% methanol (mL/g) prior to extractions using SC-CO(2) at 60 °C and 34.5 MPa. Recoveries ranged from 90 to 106% for the aromatic acids using the Na(4)EDTA-assisted SFE compared with only 7-63% recoveries of the corresponding chemicals when no Na(4)EDTA was used. The method quantitatively extracted 2,4-D and its close analogues aged in the soil for 2-30 days. The Na(4)EDTA-assisted SFE was also adequate for extracting phenolic analytes including picric acid and pentachlorophenol with recoveries from 85 to 104%. Na(4)EDTA is a good enhancer for extraction of the 29 analytes representing a wide range of polarity from the soil using SC-CO(2). The method is valuable for the analysis of parent pollutants and transformed products, particularly oxygen-borne metabolites in the environment.     

Correlation between Extraction Equilibrium of Uranium(VI) and Density of CO(2) Medium in a HNO(3)/Supercritical CO(2)-Tributyl Phosphate System

The extraction equilibrium of U(VI) between a nitric acid solution and a supercritical CO(2) phase containing tributyl phosphate (TBP) is formulated taking into account that (i) a distribution ratio of a metal extracted is a function of a distribution constant of each component involved in the extraction reaction, (ii) the distribution constant is defined as a ratio of solubilities of the component in both phases, and (iii) the solubility in the CO(2) phase is correlated with density of CO(2). A simple linear relationship between the distribution ratio, D(U), of U(VI) and density, ρ, of CO(2) is derived; log D(U) = a log ρ + A + B, in which a is a proportional constant implying the solvation characteristic of the solute in supercritical CO(2), A is a pressure-independent constant, and B is a variable determined by the distribution equilibrium of HNO(3). The equation derived was verified experimentally by the measurement of the distribution ratio of U(VI) and HNO(3) under various conditions of pressure and temperature. A novel concept of selective supercritical fluid extraction of metals by means of pressure-tuning or CO(2) density-tuning was proposed.