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1.
Summary Adding various components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the solvating properties. Polar samples which are difficult to analyze with pure supercritical CO 2 because of their high polarity can be separated by addidng polar modifiers. In this paper, a new mixing method using an HPLC filter for adding polar modifier to CO 2 is described. Although several filters were tried, only one could keep the amount of modifier in the mobile phase constant for a long time. The amount of water or methanol dissolved in supercritical CO 2 was measured by an amperometric microsensor made of a thin film of perfluorosulfonate ionomer (PFSI). 相似文献
2.
Supercritical fluid extraction was coupled directly with high performance liquid chromatograph. The system was evaluated for direct injection of supercritical CO 2 and modified supercritical CO 2 at high pressure and temperature onto a HPLC system with varying mobile phase compositions and flow rates. Injection of 9 μL supercritical CO 2 onto the HPLC using methanol/water mobile phases from 100% methanol to 80% with a flow of 1.0 mL/min did not adversely affect the baseline of UV detector. However at higher percentages of water, CO 2 solubility in the mobile phase decreased and caused baseline interferences on the UV detector. At higher HPLC mobile phase flow rates, supercritical CO 2 was injected to higher percentages of water without any effect on the UV baseline. Also, increasing the extraction pressure or modifier concentration did not change the results. Separations of polynuclear aromatic hydrocarbons and linear alkenebenzene sulfonate test mixtures were obtained using on-line SFE/HPLC interfaced system. 相似文献
3.
Abstract Adding additional components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the fluid solvating properties. Polar samples which are difficult to be analyzed with pure supercritical CO 2 because of their high polarity can be separated by adding polar modifiers to supercritical CO 2. In this paper, a new mixing device using a teflon high capacity filter for adding polar modifiers to carbon dioxide mobile phase is introduced. This new mixing device could keep the amount of modifier in the mobile phase constant for a much longer time than a saturator column. The amount of water or methanol dissolved in supercritical CO 2 was measured by amperometric microsensor which is made of thin film of perfluorosulfonate ionomer(PFSI). 相似文献
4.
A new device to accurately deliver a small amount of methanol into supercritical carbon dioxide fluid is described. Carbon dioxide, the most widely used mobile phase in supercritical fluid chromatography, is a relatively non-polar fluid, and hence the addition of a small amount of methanol could change the solvent strength of the mobile phase. In this work, supercritical CO 2 and methanol are delivered from the pump to a 100-μl mixing chamber in which a small magnetic bar is rotating. After passing through the mixing chamber, supercritical CO 2 is changed to a new mobile phase with different polarity. The modified mobile phase was successfully used for the separations of polar compounds and polyaromatic hydrocarbons (PAHs). 相似文献
5.
Summary The retention behavior of a set of polycyclic aromatic hydrocarbons in supercritical fluid chromatography have been studied
on a chemically bonded stationary phase based upon a side chain liquid crystalline polymer (LCP) with carbon dioxide-based
mobile phase. The effects of the mobile phase pressure, column temperature and amount of mobile phase organic modifier have
been investigated in order to detect a possible structural change in the liquid crystal polymer linked to the silica support.
The influence of these factors on the selectivity coefficients has also been studied. Two distinctive behaviors with temperature
are noted at low pressure on the one hand and at higher pressure on the other. This change in behavior is based on the density
of the supercritical CO 2 and the PAH volatility rather than on any specific stationary phase structural change. Both lower mobile phase pressure and
amount of mobile phase modifier are required to obtain better selectivities. Better planarity recognition is observed in SFC
than in HPLC with these new bonded liquid crystal stationary phases. The bonded liquid crystal phase is only weakly affected
by the addition of organic modifier in the supercritical CO 2. 相似文献
6.
Supercritical CO 2 is widely used in many fields of industry. Investigation of statistical mechanics of CO 2 fluid under quasi critical and supercritical state has great significance. Equilibrium molecular dynamics (EMD) simulations are carried out to investigate the statistical mechanics and macroscopic performance of CO 2 fluid under the quasi critical and supercritical state. The results show that the bond length and bond angle distributions for supercritical CO 2 are Gaussian distribution basically. The dimers’ proportion of supercritical CO 2 system changes with pressure increasing. T-type dimer has high share within the system when pressure is higher than 9MPa. It can be inferred that T-type dimer leads to CO 2 physical properties changing tempestuously under supercritical state. The effect that lubricating oil has on microstructure and heat transfer of supercritical CO 2 is also investigated in the present work. The results show the lubricating oil produces significant effect on the dimers’ structure under low pressure. 相似文献
7.
Abstract A simple heat driven pump for in-the-field supercritical fluid extraction was constructed and evaluated. The pump pressurized CO 2 from a standard (54 atm) siphon tube supply cylinder to over 400 atm. Pressurization was achieved and maintained by cyclic heating of a pump chamber containing CO 2 to 250°C then cooling and refilling the pump chamber with CO 2. The pressurized CO 2 was transferred to a heated reservoir from which the CO 2 flowed into the extraction cell. Pulse free pressure was maintained in the extraction cell indefinitely at 135 atm with a back pressure regulator. The pressure variation of the solvent delivered to the extraction cell during this period was negligible. The total weight of the system was 5.5 Kg. 相似文献
8.
A method using derivatization and supercritical fluid extraction coupled with gas chromatography was developed for the analysis of dimethylarsinate, monomethylarsonate and inorganic arsenic simultaneously in solid matrices. Thioglycolic acid n‐butyl ester was used as a novel derivatizing reagent. A systematic discussion was made to investigate the effects of pressure, temperature, flow rate of the supercritical CO 2, extraction time, concentration of the modifier, and microemulsion on extraction efficiency. The application for real environmental samples was also studied. Results showed that thioglycolic acid n‐butyl ester was an effective derivatizing reagent that could be applied for arsenic speciation. Using methanol as modifier of the supercritical CO 2 can raise the extraction efficiency, which can be further enhanced by adding a microemulsion that contains Triton X‐405. The optimum extraction conditions were: 25 MPa, 90°C, static extraction for 10 min, dynamic extraction for 25 min with a flow rate of 2.0 mL/min of supercritical CO 2 modified by 5% v/v methanol and microemulsion. The detection limits of dimethylarsinate, monomethylarsonate, and inorganic arsenic in solid matrices were 0.12, 0.26, and 1.1 mg/kg, respectively. The optimized method was sensitive, convenient, and reliable for the extraction and analysis of different arsenic species in solid samples. 相似文献
9.
Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO 2 extraction or liquid CO 2 of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO 2 (Sc CO 2) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field. 相似文献
10.
A simple interface between a capillary supercritical fluid chromatograph and an Extranuclear Simulscan mass spectrometer is described. The SFC column is directly inserted into the ion source through the existing GC-interface. The system is equipped with a splitting device which allows simultaneous EI/MS and flame ionization detection when CO 2 is used as the supercritical phase. The effect of source temperature and pressure on CO 2 clustering was studied for optimization of source conditions. The performance of the system was evaluated with a series of model compounds and standard mixtures. 相似文献
11.
The intact plant parts and genetically modified hairy root clone #TpA6 of Tagetes patula were extracted with supercritical fluid CO 2 extraction (SFE) and a conventional solvent extraction. SFE optimization included the variation of fluid CO 2 pressure, dynamic time, and the addition of methanol modifier co-solvent. The four characteristic thiophene metabolites, 5-(3-buten-1-ynyl)-2,2′-bithienyl (BBT), 2,2′:5′,2″-terthiophene (α-T), 5-(4-acetoxy-1-butynyl)-2,2′-bithienyl (BBTOAc), and 5-(3,4-diacetoxy-1-butynyl)-2,2′-bithienyl [BBT(OAc) 2], were analysed by GC–MS. The proposed SFE method allowed the selective extraction of thiophenes in 60 min dynamic time with supercritical CO 2 without modifier co-solvent, at 30 MPa and 40 °C. The SFE and the reference solvent extraction yielded similar results. The SFE of intact roots and flowers yielded 717 ± 31.3 and 480 ± 26.6 μg g ?1 α-T, respectively, while the leaves did not contain considerable amounts of thiophenes. Remarkable amounts of BBT, BBTOAc, and BBT(OAc) 2 were characteristic of the SFE of hairy root cultures. 相似文献
12.
Summary The separation of amino compounds by supercritical fluid chromatography (SFC) is a difficult problem to solve, owing to the apolar nature of CO 2. The derivatization of amino functions with the 9-fluorenylmethyl chloroformate (FMOC-Cl) allows to obtain apolar UV-absorbing compounds easily eluted with a supercritical mobile phase. Optimization of derivatization parameters allows us to analyze quantitatively amphetamines and catecholamines. These compounds can be separated in less than 5 min with a small addition of methanol as polar modifier. The total procedure takes no more than 15 min and can be automatized to gain time. As presented in this study, this method can be employed to physiological fluids as urine. 相似文献
13.
The dependent relation between temperature and pressure of supercritical CO 2+ ethanol binary system under the pressure range from 5 to 10 MPa with the variety of densities and mole fractions of ethanol
that range from 0 to 2% was investigated by the static visual method in a constant volume. The critical temperature and pressure
were experimentally determined simultaneously. The PTρ figures at different ethanol contents were described based on the determined pressure and temperature data, from which pressure
of supercritical CO 2 + ethanol binary system was found to increase linearly with the increasing temperature. P-T lines show certain convergent feature in a specific concentration of ethanol and the convergent points shift to the region
of higher temperature and pressure with the increasing ethanol compositions. Furthermore, the effect of density and ethanol
concentration on the critical point of CO 2 + ethanol binary system was discussed in details. Critical points increase linearly with the increasing mole fraction of
ethanol in specific density and critical points change at different densities. The critical compressibility factors Z c of supercritical CO 2 + ethanol binary systems at different compositions of ethanol were calculated and Z
c
-ρ figure was obtained accordingly. It was found from Z
c
-ρ figure that critical compressibility factors of supercritical CO 2 unitary or binary systems decline linearly with the increasing density, by which the critical point can be predicted precisely. 相似文献
14.
Summary Several investigations were performed to optimise the extraction of polar triazine herbicides using supercritical fluid extraction from two different solid matrices: C 18-silica and soil samples. Supercritical CO 2 modified with methanol [10% (VV)] at 250 bars and 50°C was required to quantitatively extract Atrazine and 2-Hydroxyatrazine from spiked C 18-silica. Extraction of Desisopropyl-desethyl-2-hydroxyatrazine (MET) attained only 52%, even following addition of water to the polar modifier. Extractions of spiked soil samples (20 ppm of each pesticide) were successful at 300 bars and 65°C. A non polar wash improved the recoveries of the three target analytes [i.e. atrazine: 88%; 2-hydroxyatrazine: 96%; MET: 41%]. The extraction parameters employed are discussed in this paper. 相似文献
15.
In the extraction of spiked PCB from soil, three extracting fluids were investigated: supercritical carbon dioxide (CO 2), supercritical sulfur hexafluoride (SF 6) and subcritical water. Among the tested fluids SF 6 appeared to be appropriate especially for the extraction of low polar PCB. CO 2 and water were found to be suitable for the quantitative extraction of all PCB. Water was judged as the best because of its low price, good availability and environmental safety. 相似文献
16.
The intact plant parts and genetically modified hairy root clone #TpA6 of Tagetes patula were extracted with supercritical fluid CO2 extraction (SFE) and a conventional solvent extraction. SFE optimization included the variation of fluid CO2 pressure, dynamic time, and the addition of methanol modifier co-solvent. The four characteristic thiophene metabolites, 5-(3-buten-1-ynyl)-2,2′-bithienyl (BBT), 2,2′:5′,2″-terthiophene (α-T), 5-(4-acetoxy-1-butynyl)-2,2′-bithienyl (BBTOAc), and 5-(3,4-diacetoxy-1-butynyl)-2,2′-bithienyl [BBT(OAc)2], were analysed by GC–MS. The proposed SFE method allowed the selective extraction of thiophenes in 60 min dynamic time with supercritical CO2 without modifier co-solvent, at 30 MPa and 40 °C. The SFE and the reference solvent extraction yielded similar results. The SFE of intact roots and flowers yielded 717 ± 31.3 and 480 ± 26.6 μg g−1 α-T, respectively, while the leaves did not contain considerable amounts of thiophenes. Remarkable amounts of BBT, BBTOAc, and BBT(OAc)2 were characteristic of the SFE of hairy root cultures. 相似文献
17.
The free‐radical grafting of maleic anhydride (MAH) and styrene (St) onto isotactic polypropylene (iPP) was studied by thermal decomposition of dicumyl peroxide (DCP) using supercritical CO 2 as a solvent and swelling agent. Several effects of molar ratio of monomer, soaking temperature and time, reaction time, and reaction pressure on the graft degree were discussed. It was found that the addition of St to the grafting system as a comonomer could significantly enhance the graft degree of the grafted PP. Under the optimal reaction condition, the maximum of iPP grafting MAH and St in supercritical CO 2 medium was 10.58%. The chemical structures and properties of grafting copolymers were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The results showed that the supercritical CO 2 method had noticeable advantages over the existed method when compared, such as a lower temperature, a higher graft degree, easy separation, and environmentally benign. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
18.
Seeds and leaves of cultivated great plantain ( Plantago major L.) were extracted with conventional Soxhlet extraction using a variety of solvents and with pilot scale supercritical fluid (CO 2) extraction (SFE-CO 2). Hydroxy pentacyclic triterpene acids (HPTAs), oleanolic acid and ursolic acid, were identified from the SPE purified extracts with LC-(UV)-APCI-MS and quantified with LC-UV. Dried P. major leaves contained 0.07% of oleanolic acid and 0.22% of UA. Seeds had very small amounts of HPTAs, 0.005% of OA and 0.007% of ursolic acid in the oil extracted. SFE-CO 2 extraction without polar modifier was found not to be a suitable technology for the leaf extraction due to the low content of lipophilic and volatile compounds. Soxhlet extraction with diethyl ether and SFE-CO 2 extraction were similar in the efficiency of extracting HPTAs from the seeds. 相似文献
19.
An on-line supercritical fluid extraction (SFE) system coupled to a continuous flow manifold including a UV detector was used as a screening system to extract astaxanthin from crayfish, which was found to be the major carotenoid present in the samples. This compound constitutes the principal additive used to dye salmon flesh. The flow manifold was used to confirm the presence of astaxanthin in the crustacean samples. Also, an HPLC/UV-vis method was used to ascertain that this compound was the major carotenoid extracted under the optimum SFE conditions employed. The influence of SFE operating variables such as pressure, temperature, equilibration time, extraction time, trap temperature, and volume of CO 2 modifier was examined in order to maximize the efficiency of analyte extraction. The use of supercritical CO 2 enables the expeditious, selective, quantitative extraction of astaxanthin from crustaceans. 相似文献
20.
The synthesis of silica aerogels was modified by addition of supercritical CO 2 during the sol-gel process. It was shown, that CO 2 acts as a catalyst and accelerates the gelation significantly. This effect was studied under a multitude of experimental conditions. The influence of the precursor concentration, temperature and the nature of the catalysts and solvent on the gel formation in presence of CO 2 was studied. Several gels obtained by this method were dried and transparent silica aerogels were produced. 相似文献
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