Ionic liquid–modified cellulosic hydrogels for loading and sustained release of selenourea: an ensuing inhibition of tyrosinase activity

Cellulose-based hydrogel materials were prepared and modified with tannic acid and l-methionine using ionic liquid as the solvent. The gels were prepared to develop a sustained release medium for selenourea (SeU). The drug delivery characteristics of selenourea-loaded cellulose (CSeU), selenourea-loaded tannic acid-modified cellulose (CTSeU), and selenourea-loaded L-methionine-modified cellulose (CMSeU) were investigated in aqueous media and simulated gastric fluid (SGF) media. This modified gel beads have been characterized using field emission scanning electron microscope, X-ray energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis and swelling properties and compared with those of the unmodified ones. We also investigated the inhibitory effects of SeU released from these gels on the activity of mushroom tyrosinase. Out of all the gel materials, CTSeU showed maximum SeU release both in water and SGF media. However, tyrosinase inhibitory action in PBS medium was comparable for all the three gel materials.     

The dependence of sorbent/analyte type on observed differences in supercritical fluid extraction efficiencies employing extraction vessels of different dimensions

Summary The effect of extraction cell dimensions (i.d.: length) on supercritical fluid extraction (SFE) efficiencies of polychlorinated biphenyls (PCBs) is shown to be dependent on the type of sorbent used. For octadecylsilane (C18) sorbents, there is a significant increase in observed SFE recoveries of PCBs when the cell dimensions are made more broad (increased i.d.: length); whereas, no effect of cell geometry is observed when the common adsorbent, Florisil, is utilized. Additionally, recoveries decreased in proportion to the chlorine number, for the PCBs studied, for octadecylsilane sorbents, while no such effect was observed for Florisil. These results illustrate the magnitude of the matrix effect in SFE, which generally dominated observed recoveries, even in the simplest analyte/sorbent systems such as the one studied here.     

Analysis of Petroleum Distillates from Fire Debris Using Supercritical Fluid Extraction with a Two‐Level Orthogonal Array Experimental Design

A supercritical fluid extraction (SFE) method was developed in the present study as an effective sample pretreatment technique of petroleum distillates from fire debris. Three petroleum distillates were used as target analytes, including 95 unleaded gasoline, kerosene, and premium diesel. An orthogonal array (L16) experimental design was adopted to separately evaluate primary SFE experimental factors. The SFE efficiencies of petroleum distillates at various extraction conditions were examined and the optimized SFE conditions were identified. Experimental results demonstrated that the optimized SFE method not only provided an effective extraction method for the spiked sample, but also successfully recovered residues of petroleum distillates from fire debris.     

Diffusion coefficients of 2-fluoroanisole, 2-bromoanisole, allylbenzene and 1,3-divinylbenzene at infinite dilution in supercritical carbon dioxide

The Taylor–Aris chromatographic technique was employed for the determination of diffusion coefficients of 2-fluoroanisole, 2-bromoanisole, allylbenzene and 1,3-divinylbenzene at infinite dilution in supercritical carbon dioxide from 313.16 to 333.16 K and pressures between 15 and 35 MPa. As expected, the diffusivities rise when temperature increases and pressure decreases. Numerous predictive equations are compared with experimental data: Lai–Tan, Liu–Ruckenstein cluster formula, Woerlee, Hippler–Schubert–Troe, Catchpole–King, Eaton–Akgerman, He, He–Yu, Liu–Silva–Macedo, Funazukuri and coworkers, Dariva–Coelho–Oliveira, Zhu–Lu–Zhou–Wang–Shi and the Liu–Ruckenstein RHS formula. The equations of He, He–Yu and Catchpole–King are the best of all, but cannot be used in the whole range of temperatures and solvent densities.     

A model for quantitatively describing linear velocity programming in capillary SFC

Summary Linear velocity in capillary SFC is commonly controlled by restricting capillaries. In this paper, a model is described that quantitatively predicts the linear velocity of a supercritical fluid in SFC using tapered or ceramic frittype restrictors. In this model, the flow from the restricting capillary is assumed to be an isentropic expansion. The variation of the linear velocity as a function of pressure, temperature and cross-sectional area of the restricting aperture was predicted by this model. This predictive capability is important to the use of gradient programming in capillary SFC. Finally, the ideal variable restrictor for gradient programming was found to be one that could reversibly increase or decrease the linear velocity independent of the pressure, temperature, and/or density conditions used to create the gradient.     

不同干燥过程对超细TiO2粉体性质的影响

考察了采用不同干燥工艺制备的TiO2粉体在粒子形貌、颗粒大小与分布、晶相组成以及比表面积和孔结构等织构和结构性质方面的差异。结果表明，利用常规的干燥方法，由水凝胶脱水所得的颗粒，颗粒间严重团聚，颗粒粒径大且分布不均匀，比表面积和孔体积最小；由醇凝胶直接脱水，则可以显著提高粉体的织构性能．而采用超临界流体干燥法则可以进一步提高粉体的性能，比表面积由水凝胶的4．88m2·g－1增大到113．8m2·g－1，提高了近30倍；孔体积由0．027cm3·g－1增大到0．41cm3·g-1．大约提高了15倍；而且其能够有效地防止粒子间的团聚，较好地保持了湿凝胶的网络结构，使颗粒尺寸降低且分布均匀，可重复性好．     

Evaluation of dithiocarbamates and beta-diketones as chelating agents in supercritical fluid extraction of Cd, Pb, and Hg from solid samples

The use of four dithiocarbamates and three fluorinated β-diketones as potential chelating agents for three transition metal ions (Cd²⁺, Pb²⁺, and Hg²⁺) extracted from spiked sand and filter paper samples by supercritical fluid extraction (SFE) was investigated. The extractions were performed at 45°C and 250 atm for spiked sand samples and at 60°C and 200 atm for filter paper samples using supercritical carbon dioxide modified with 5% methanol. At 250 atm and using carbon dioxide modified with 5% methanol, the recoveries of Cd²⁺, Pb²⁺, and Hg²⁺ ions from spiked sand samples were 95% with lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC) as the chelating agent; they ranged from 83–97% with diethylammonium diethyldithiocarbamate and from 87–97% with sodium di-ethyldithiocarbamate as chelating agents, and from 68–96% with trifluoracetylacetone, hexafluoroacetylacetone, and thenoylfluoroacetone as chelating agents. Ammonium pyrrolidinedithiocarbamate was not effective in the chelation SFE of Cd²⁺, Pb²⁺, and Hg²⁺ ions from either spiked sand or spiked filter paper samples under the extraction conditions used. Supercritical carbon dioxide alone gave consistently lower analyte recoveries than supercritical carbon dioxide modified with 5% methanol. The results suggest that the solubility of the metal chelate in the supercritical fluid plays a more important role than the solubility of the chelating agent in the supercritical fluid, as long as sufficient chelating agent is present in the fluid phase. Fluorination of the chelating agent, as in the case of LiFDDC, increases the solubility of the metal chelate, and subsequently enhances the extraction efficiency for the metal ions.     

Effect of column diameter on efficiency in capillary supercritical fluid chromatography

Fused silica capillary columns with internal diameters from 100 to 25 μm were coated with SE-54 and evaluated under supercritical fluid chromatographic conditions using carbon dioxide as mobile phase. Experimental results compared well with theoretical predictions. At ten times the optimum mobile phase velocity and for a capacity factor, k of 3, efficiencies of 2300 to 5600 plates m^?1 were obtained for column diameters of 100 to 25 μm, respectively.     

Analysis of turkish lignite tar by coupled LC/GC,GC/MS,and capillary SFC

This work describes the analysis of a pyrolysis product of a lignite sample obtained from the Turkish Goynuk reserve. The aliphatic, aromatic and polar compounds present in the tar are separated and identified by various chromatographic techniques: Capillary gas chromatography/mass spectrometry (GC/MS), on-line high performance microbore liquid chromatography/capillary gas chromatography (LC/GC) and capillary supercritical fluid chromatography (SFC). The suitability of each technique for this particular application is discussed, and semi-quantitative results are presented for the major components detected.     

超临界萃取装置的研制及其应用

超临界流体萃取是近的上来兴起的一种新的分离技术，报道了将超临界萃取原理与回流技术相结合研制的二氧化碳回流中低压超临界流体萃取设备，解决了关键实验手段，通过应用证明设备可靠，费用低廉，有实用价值。