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11.
Akiba Y Beavis D Beery P Britt HC Budick B Chasman C Chen Z Chi CY Chu YY Cianciolo V Cole BA Costales JB Crawford HJ Cumming JB Debbe R Engelage J Fung SY Gonin M Gushue S Hamagaki H Hansen O Hayano RS Hayashi S Homma S Kaneko H Kang J Kaufman S Kehoe WL Kurita K Ledoux RJ Levine MJ Miake Y Morrison DP Morse RJ Moskowitz B Nagamiya S Namboodiri MN Nayak TK Olness J Parsons CG Remsberg LP Roehrich D Rothschild P Sakurai H Sangster TC Seto R Soltz R Stankus P Steadman SG Stephans GS Sung T 《Physical review letters》1996,76(12):2021-2024
12.
To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4. Baseline separation of anions commonly found in beverage drinks could be achieved in less than 14 min with indirect UV detection at 240 nm. Comigration problems for hydroxycarboxylic acids could be solved using TEPA as BGE additive. The results indicate excellent repeatability for migration time (RSD, 0.27-0.67%, n = 5) and good precision for both peak height (RSD, 3.2-4.2%, n = 5) and peak area (RSD, 3.1-4.5%, n = 5). Under the optimized conditions and using corrected peak area for quantitation, an excellent linear dynamic range (with correlation coefficient > 0.997 in a concentration range from 0.005 to 2.0 mmol/L) and low detection limit (1-4 micro mol/L) were obtained for all the anions investigated. The applicability and reliability of the CE procedure developed were established by parallel method determination using established ion chromatography procedure for the analysis of inorganic and organic acid anions in orange juice and wine samples. Our CZE procedure provided a sensitive and economic technique for simultaneous determination of inorganic and organic acid anions in orange juice, red and white wine samples. 相似文献
13.
A fully automated nanoelectrospray tandem mass spectrometric method for analysis of Caco-2 samples 总被引:1,自引:0,他引:1
Van Pelt CK Zhang S Fung E Chu I Liu T Li C Korfmacher WA Henion J 《Rapid communications in mass spectrometry : RCM》2003,17(14):1573-1578
Caco-2 cells offer a means to rapidly screen permeability of drug candidates, allowing pharmaceutical companies to eliminate candidates unable to cross the intestinal barrier early in the discovery process. This screening process is typically performed by conventional liquid chromatography/tandem mass spectrometry (LC/MS/MS), which can require time-consuming method development. An alternative to LC/MS/MS, automated nanoelectrospray tandem mass spectrometry (nanoESI-MS/MS), is introduced. This novel approach requires an off-line ZipTip desalting step followed by automated nanoESI-MS/MS, using the NanoMate 100 and ESI Chip. In addition to reduced method development time, automated nanoESI-MS/MS also offers no carry-over between samples, low sample consumption, and ease-of-use as compared with conventional pulled-capillary nanoelectrospray. Furthermore, the infusion system described has the potential to be high-throughput. A comparison of Caco-2 samples analyzed both by LC/MS/MS and by automated nanoESI-MS/MS is presented. The permeability and recovery data of the two compounds analyzed in this study obtained from conventional LC/MS/MS and by automated nanoESI-MS/MS were in excellent agreement. 相似文献
14.
15.
To understand the cation-pi interaction in aromatic amino acids and peptides, the binding of M(+) (where M(+) = Li(+), Na(+), and K(+)) to phenylalanine (Phe) is studied at the best level of density functional theory reported so far. The different modes of M(+) binding show the same order of binding affinity (Li(+)>Na(+)>K(+)), in the approximate ratio of 2.2:1.5:1.0. The most stable binding mode is one in which the M(+) is stabilized by a tridentate interaction between the cation and the carbonyl oxygen (O[double bond]C), amino nitrogen (--NH(2)), and aromatic pi ring; the absolute Li(+), Na(+), and K(+) affinities are estimated theoretically to be 275, 201, and 141 kJ mol(-1), respectively. Factors affecting the relative stabilities of various M(+)-Phe binding modes and conformers have been identified, with ion-dipole interaction playing an important role. We found that the trend of pi and non-pi cation bonding distances (Na(+)-pi>Na(+)-N>Na(+)-O and K(+)-pi>K(+)-N>K(+)-O) in our theoretical Na(+)/K(+)-Phe structures are in agreement with the reported X-ray crystal structures of model synthetic receptors (sodium and potassium bound lariat ether complexes), even though the average alkali metal cation-pi distance found in the crystal structures is longer. This difference between the solid and the gas-phase structures can be reconciled by taking the higher coordination number of the cations in the lariat ether complexes into account. 相似文献
16.
A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of both organic and inorganic anions in rain water using a background electrolyte (BGE) containing 5 mM molybdate, 0.15 mM CTAH, 0.01% PVA and 5 mM Tris buffer to adjust pH at 7.9. Under optimised conditions, good repeatability (RSD for sulphate in migration time=0.36% and peak area=4.2%), low detection limit (2 ppb for chloride) and satisfactory working range (50 ppb-20 ppm for hydrodynamic injection, 10 ppb-3 ppm for electrokinetic injection for chloride) were obtained. The reliability of the CE procedure developed was established by satisfactory recovery tests and good agreement of results obtained by both the CE and ion chromatography (IC) methods. The procedure developed had been successfully applied for field monitoring of rainwater showing good repeatability and capability of detecting trace anions at ppb levels beyond the IC working range. Thus, the new CE procedure developed provides a quick, sensitive, economic and reliable method to meet the need for the simultaneous determination of both organic and inorganic anions in the acid rain monitoring programme. 相似文献
17.
Chen Hui Sharma Sunil K. Sharma Priyanka R. Chi Kai Fung Eric Aubrecht Katherine Keroletswe Ngonye Chigome Samuel Hsiao Benjamin S. 《Cellulose (London, England)》2021,28(13):8611-8628
Cellulose - Mercury contamination in drinking water is a worldwide problem due to its severely harming effects on the human body. A nanostructured natural bioadsorbent, carboxycellulose nanofiber... 相似文献
18.
Zucheng Wu Ying Sing Fung 《International journal of environmental analytical chemistry》2013,93(7):431-442
The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water. 相似文献
19.
Abstract An N.M.R. method combining the techniques of separated local field spectroscopy (SLF) and variable angle spinning (VAS) is valuable in the investigtion of nematic liquid crystals. Rapid sample spinning causes the nematic director to align along the spinning axis, resulting in narrow peaks in the C-13 N.M.R. spectrum. SLF is a two-dimensional N.M.R. method which produces a first order splitting pattern for each carbon signal from which C–H dipolar coupling constants can be determined. The order parameters for all segments of the liquid crystal molecule can then be calculated. Results for three 4′-cyanophenylcyclohexanes are considered here. These compounds are trans-substituted at the 4 position of cyclohexane ring with n-pentane (PCH5), 1-pentene (3d 1CP) and 3-pentene (1d 3CP), respectively. 相似文献
20.
Abstract Three new homologous series of mesogens containing three rings in the main structure and a lateral aromatic branch have been synthesized. When the lateral aromatic branch is attached to the middle ring, monotropic phases are observed, and there is a strong tendency to form the smectic C phase. When the lateral aromatic branch is attached to an outer ring, the compounds possess purely enantiotropic nematic phases. The terminal alkoxy chain in the outer ring which has a lateral aromatic substituent can be replaced by a rigid group without disturbing the large nematic range. Selective introduction of a particular substitutent may be useful for the construction of devices possessing desirable characteristics such as non-linear optical properties. 相似文献