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91.
郭冰 柳卫平 Trinczek M Lapi S Ames F Buckley K R D’Auria J M Jayamanna K Ruiz C Ruth T J 《中国物理 C》2006,30(7):675-679
加拿大TRIUMF实验室利用11C成功验证了一种产生高强度(~108ions/s)放射性束流的方法. 该方法不同于普通在线同位素分离方法, 它利用了13MeV的低能强流质子束, 可以产生一系列核天体物理实验感兴趣的高强度放射性束流. 相似文献
92.
93.
Both homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO2, O2, and N2 using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO2 relative to N2, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO2 in homogeneous membranes obeys the dual-mode mobility model. The ideal separation factor for CO2 relative to N2 at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO2 is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc. 相似文献
94.
Chiral separations by host-guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis 总被引:2,自引:0,他引:2
Summary Capillary zone electrophoresis using cyclodextrins and a chiral crown ether as buffer constituents was studied for the enantiomeric separation of drugs and amino acids. Based on results obtained from separation of racemic -amino acids both chiral selectors are compared with respect to resolution, efficiency and retention time. For (±)-Quinagolide effects of buffer composition and temperature are examined using -cyclodextrin as chiral agent. Optimum conditions were pH 2.5 at 30 mmol L–1 -cyclodextrin. A linear dependence of retention on -cyclodextrin concentration allowed calculation of formation constants of the host-guest complexes. Buffer concentration and temperature also influence resolution. The application of a chiral crown ether to the separation of optical isomers in capillary zone electrophoresis is described for the first time. Chiral recognition of solutes depends on the formation of protonated alkyl amines and separation is attributed to the formation of diastereomeric host-guest complexes with different interactions for each enantiomer. The effects of crown ether concentration on resolution are presented. 相似文献
95.
96.
Takuji Hirose Kumiko Naito Megumi Nakahara Hiroaki Shitara Yoshio Aoki Hiroyuki Nohira Bruce W. Baldwin 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):87-93
Two Kemp's acid diamides were synthesized and applied to chiral amine recognition using 1H NMR analysis. One derivative based on 1-(1-naphthyl)ethylamine had good chiral recognition of six amines and was useful to determine the optical purity for three amines, i.e., methylbenzylamine, 1-(1-naphthyl)ethylamine and 1- henylpropylamine,however, the cyclohexylethylamine derivative showed little discrimination for the amines studied. Together with the results for alkylamines, it was shown that aromatic structure was important for aromatic shielding anisotropy and –– interactions between host and guest. The structure of the 1-(1-naphthyl)ethylamine derivative in solution was also considered based on 1H NMR data and computer simulation. 相似文献
97.
手性配体立体选择性萃取分离扁桃酸对映体 总被引:6,自引:0,他引:6
Based on chiral ligand exchange, the distribution behavior of mandelic acid enantiomers in the two-phase system containing copper ion(Ⅱ)(Cu2+) and N-n-dedecane-L-hydroxyproline (L), was studied. At different pH, the partition of Cu2+ in the two-phase system containing N-n-dedecane-L-hydroxyproline, was investigated. The formation constant of binary cpmplex(Li2Cu) was obtained by regression. The influence of pH, concentrations of Cu2+ and chiral ligand, and solvents on partition coefficients(K) and separation factor(α), was discussed. The experimental results show that Li forms more stable ternary complex with D-mandelic acid than with L- mandelic acid. There is a large influence of pH on K and α. At low pH values (<3.5), formation of binary complexes is thermodynamically unfavourable. K and α are best when pH values are above 3.5 and the molar ratio of chiral ligand to Cu2+ is 2∶1. At the same time, solvents influence K and α very much. 相似文献
98.
99.
Two greener procedures for flow-injection spectrophotometric determination of nitrite in natural waters were developed and critically compared. Replacement of toxic reagents, waste minimization and treatment were exploited to attend the standards of clean chemistry. The flow system was designed with solenoid micro-pumps in order to minimize reagent consumption and waste generation. The first procedure is based on the Griess diazo-coupling reaction with sulfanilamide and N-(1-naphthyl)ethylenediamine (NED) yielding an azo dye, followed by photodegradation of the low amount of waste generated based on the photo-Fenton reaction. The second procedure is based on the formation of iodine from nitrite and iodide in acid medium in order to avoid the use of toxic reagents. For Griess method, linear response was achieved up to 1.0 mg L− 1, described by the equation A = − 0.007 + 0.460C (mg L− 1), r = 0.999. The detection limit was estimated as 8 μg L− 1 at the 99.7% confidence level and the coefficient of variation was 0.8% (n = 20). The sampling rate was estimated as 108 determinations per hour. The consumption of the most toxic reagent (NED) is reduced 55-fold and 20-fold in comparison to batch method and flow injection with continuous reagent addition, respectively. A colorless residue was obtained by in-line photodegradation with reduction of 87% of the total organic carbon content. The results obtained for natural water samples were in agreement with those achieved by the reference method at the 95% confidence level. For the nitrite–iodide method, linear response was observed up to 2.0 mg L− 1, described by the equation A = − 0.024 + 0.148C (mg L− 1), r = 0.999. The detection limit was estimated as 25 μg L− 1 at the 99.7% confidence level and the coefficient of variation was 0.6% (n = 20). The sampling rate was estimated as 44 determinations per hour. Despite avoiding the use of toxic reagents, the nitrite–iodide method presented worst performance in terms of selectivity and sensitivity. 相似文献