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991.
S. J. Yeh C. S. Tsai H. T. Yang 《Journal of Radioanalytical and Nuclear Chemistry》1995,192(1):163-170
A preconcentration method of 13 rare earth elements (REES) was studied for neutron activation ananlysis (NAA). Hydrated magnesium oxide was used as the preconcentration agent to absorb the REES ions from aqueous solution onto the solid magnesium oxide, which was separated and analyzed. It was observed that the Langmuir equation for isothermal adsorption was well obeyed by the REES under the condition studied. The efficiency of the preconcentration process using hydrated magnesium oxide was critically examined for each of REE and for mixture of REES by preparing a known volume of solution containing known amount of trace REES. NAA was used to analyze REES recovered by the preconcentration process. It was found that the REES recoveries were satisfactory and the preconcentration process is reliable. There are several resort resort areas in Taiwan where local people are enjoying its hot spring water. It is generally believed that the hot spring water spa would bring about some sorts of therapeutic functions. The preconcentration method developed above, was applied to analyze the trace amounts of REES in hot spring wate in Taiwan. 相似文献
992.
Identification and determination of geniposide contained in Gardenia jasminoides and in two preparations of mixed traditional Chinese medicines 总被引:7,自引:0,他引:7
A high-performance liquid chromatographic method was applied to the determination of the geniposide concentration in Gardenia fruit and preparations of traditional Chinese medicine using a mobile phase of acetonitrile-methanol-5 mM monosodium phosphate (pH 4.6) (5:15:80, v/v/v). Intra-assay and inter-assay accuracy and precision of the analyses were < or = 10% in the range of 0.1 through 50 microg/ml. The presence of geniposide in the medicinal herb and its preparations was ascertained by retention time, spiking with an authentic standard, change of detection wavelength and change of the composition of the mobile phase. The concentration of geniposide in the fruit of Gardenia jasminoides Ellis var. grandiflora Nakai is higher than that in Gardenia jasminoides Ellis. The concentration of geniposide in the traditional Chinese herbal medicine preparations, Huang-Lian-Jiee-Dwu-Tang (66.27 +/- 1.98 mg/g) and In-Chern-Hau-Tang (68.54 +/- 2.62 mg/g) was less than in the herb Gardenia jasminoides Ellis (73.44 +/- 2.62 mg/g) itself. 相似文献
993.
Measurement and pharmacokinetic analysis of unbound cephaloridine in rat blood by on-line microdialysis and microbore liquid chromatography 总被引:2,自引:0,他引:2
A technique involving rapid sampling of cephaloridine in rat blood was achieved using a combination of microdialysis and sensitive microbore liquid chromatography. A microdialysis probe was inserted into the jugular vein/right atrium of a Sprague-Dawley rat. Then after a real-time collection of the analyte by microdialysis, the dialysate was automatically injected into a liquid chromatographic system via an on-line injector. Following a 2 h stabilization period after the surgical procedure, cephaloridine (20 mg/kg, i.v.) was then administered via the femoral vein. Isocratic elution of cephaloridine was carried out with a mobile phase containing methanol-20 mM monosodium phosphate (25:75, v/v, pH 5.5), and the flow rate of the mobile phase was 0.05 mL/min within 10 min. Intra- and inter-assay accuracy and precision of the assay were each less than 10%. The in vivo recovery of the cephaloridine from the microdialysate was 49.7 +/- 8.0% and 42.4 +/- 8.4% for 0.5 and 1 microg/mL standards (n = 6), respectively. Based on the pharmacokinetic analysis, the elimination half-life was 32.2 +/- 8.6 min by cephaloridine administration (20 mg/kg, i.v., n = 6). 相似文献
994.
Formation constants of Li+ complexes with 4-substituted dibenzo-14-crown-4 (DB14C4; 4-substituted group: methyl-, tert-butyl-, H-, bromo-, chloro-, formyl-, nitro-) ligands were determined by 7Li NMR spectrometry for solutions in nitromethane (NM), acetonitrile (ACN), propylene carbonate (PC), acetone (AC), Pyridine (Py), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and N,N′-dimethyl formamide (DMF). Only a 1:1 complex was formed in solvents with a small or medium donor number. The formation constants of these complexes are strongly influenced by the size of the metal ion – the effect of the size of the cavity, by the solvent and by substituent. The stability of lithium ion with different substituents on DB14C4 decreases in the order methyl- > tert-butyl- > H- > bromo- > chloro- > formyl- > nitro- in various solvents. A good Hammett correlation was found by plotting log Kf vs. ∑σ in PC and AC. The extent of the substituent effect increases as the donor number of solvent decreases. The complexes were both enthalpy and entropy stabilized. The same magnitude of ΔS° value for different substituents indicates formation with a similar configuration upon complexation between crown ether and lithium ion. A slight variation in entropy contribution was observable depending on the nature of the alkyl substituent, whereas a large variation in enthalpic contribution shows a remarkable substituent effect upon complexation; the effect can reach 70% in magnitude. 相似文献
995.
Yi-Lin Jan Tsing-Hai Wang Ming-Hsu Li Shih-Chin Tsai Yuan-Yaw Wei Chun-Nan Hsu Shi-Ping Teng 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):299-306
A good understanding of the migration of selenite, Se(IV), through deep granitic layers depends on a good understanding of
the geochemistry of these layers. Chemical sequential extraction is applied herein to evaluate the ability of granite to adsorb
Se(IV) in DW, GW and SW systems. The experimental results indicate that the removal of crystalline Fe oxides reduces the adsorption
of Se(IV), suggesting its importance in granite. The normalized concentrations of Se(IV) adsorbed onto crystalline Fe oxides
is approximately 0.0301, 0.0330 and 0.0335 mole Se(IV) adsorbed/mole of Fe in DW, GW and SW systems. Kinetic adsorption experiments
are conducted to elucidate the results of the chemical sequential extraction. Both the treated and the untreated granite take
the same time to reach their equilibrium, suggesting that crystalline Fe oxides dominate the adsorption of Se(IV). Meanwhile,
the one-site model suffices to simulate the kinetics of adsorption. 相似文献
996.
Understanding the potential range of enzymatic thio effects (kO/kS) is of great value when using sulfur-substituted phosphate analogues to study phosphoryl transfer reactions in enzymes and ribozymes. Herein we report that a newly discovered Ca2+-dependent Streptomyces antibioticus phosphatidylinositol-specific phospholipase C and its mutants display unprecedented magnitudes of thio effect, inverse thio effect, and RP/SP stereoselectivity. We demonstrate that for a single enzyme the bridging thio effect can vary from 0.002 to 20 and the nonbridging thio effect can vary from 1 to 108. These values fall outside the range of those reported for nonenzymatic reactions, emphasizing the need for cautious interpretation when using thio effects to elucidate details of enzyme catalysis. 相似文献
997.
Tsai SC 《Chemistry & biology》2004,11(9):1177-1178
In this issue of Chemistry & Biology, a novel Aldol-Switch mechanism is proposed for the biosynthesis of type III polyketides, which include many antioxidants found in colorful fruits. Based on structural and mutagenesis studies, the Aldol-Switch mechanism suggests that electronic effects balance between two competing cyclization specificities in Type III polyketide synthases. A novel hypothesis is also used to explain stilbenecarboxylate biosynthesis. 相似文献
998.
Keng‐Shiang Huang Sie‐Rong Li You‐Feng Wang Yu‐Li Lin Yung‐Hua Chen Tzu‐Wei Tsai Chih‐Hui Yang Eng‐Chi Wang 《中国化学会会志》2005,52(1):159-167
Synthesis of some benzoheterocyclic compounds like substituted benzofurans, 4‐methyl‐2H‐chromenes and 3,4‐dihydro‐2H‐benzo[b]oxepin‐5‐ones from 2‐hydroxyacetophenone via base induced cyclization and ring‐closing metathesis (RCM) is described. 相似文献
999.
Sol-gel derived urease-based optical biosensor for the rapid determination of heavy metals 总被引:1,自引:0,他引:1
A urease optical biosensor for the determination of heavy metals based on sol-gel immobilization technique was developed. A fluorescent dye, FITC-dextran, was encapsulated and parameters including optical properties of the probe, relative enzyme activity, initial pH value and the buffer concentration for substrate preparation were investigated. In sol-gel immobilization, 1 mM Tris-HCl at pH 7.1 provided a sufficient buffer capacity for metal ion analysis as well as the enzyme activity maintenance. Also, two analytical procedures, incubated and un-incubated systems, were compared to understand the sensitivity and applicability to heavy metal analysis. The developed optical biosensor showed high reproducibility and the relative standard deviation (R.S.D.) of 5.1% (n=10) was obtained. Also, eight measurements can be completed automatically within 36 min. The biosensor has high sensitivity to Cu(II) and Cd(II) and an analytical range of 10-230 μM with a detection limit of 10 μM was achieved. Moreover, biological and environmental samples were examined to evaluate the applicability of the developed biosensor. A 19-82% of inhibition was observed when 20-45 μM metal ions were amended into tested samples, revealing that the developed system has the potential for the determination of heavy metals in real samples. 相似文献
1000.
In this study, a Tosflex (a perfluoro‐anion‐exchange membrane) modified glassy carbon electrode has been used to detect 2‐naphthalenol (2‐naphthol) in aqueous solutions in order to demonstrate the electroanalytical application of Tosflex. 2‐naphthol polymerizes upon electrochemical oxidation at a glassy carbon electrode; however, the current related to this oxidation is too small for analytical purpose at low concentration level. A Tosflex polymer modified glassy carbon electrode (TFGCE) was found of having capability to improve the detection limit because 2‐naphthol molecules deprotonated in basic solutions to form 2‐naphtholate anions that were accumulated to TFGCE by the anion‐exchange characteristic of Tosflex. The accumulated 2‐naphtholate anions were determined with the following differential pulse voltammetry. With 3 minutes accumulation at +0.05 V, the dependence of oxidation current versus concentration was linear from 8×10?7 M to 1×10?5 M with a regression coefficient of 0.999 and a detection limit of 2×10?7 M. Unlike many other anion‐exchange polymer modified electrodes, the TFGCE is stable at highly basic condition. 相似文献