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271.
We report an on-line sample preconcentration technique based on dynamic pH junction in capillary electrophoresis-mass spectrometry (CE-MS). For peptide analysis, the samples were dissolved in a solution with higher pH than the background solution (BGS), and were injected into the capillary as a long plug. The pH difference between the sample matrix and BGS caused changes in analytes' mobilities during electrophoresis, resulting in narrowing of their bands at the boundary. Around 550-1000-fold sensitivity enhancement could be achieved in terms of peak intensity without degrading peak shape and resolution. This technique is easy to perform and will be useful for peptide mass fingerprinting in protein analysis. 相似文献
272.
Koich Akiyama Nobuyuki Tomita Yoshinori Nomura Toshiro Isu Hajime Ishihara Kikuo Cho 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We demonstrate a remarkable thickness dependence of nonlinear optical response of exciton–polaritons in GaAs thin films by degenerate four-wave mixing (DFWM) at low temperature (T=5 K). High-quality samples of layer thickness from 80 to 200 nm were grown by molecular beam epitaxy. Confined mode of the exciton–polariton dominantly contributed to the reflection spectra, which were examined by the calculation using a transfer matrix method. The DFWM intensity at exciton resonance was enhanced at a particular thickness (110 nm). This thickness dependence is in good agreement with the nonlocal theory, which shows a remarkable size dependence of the internal field relevant to the confined mode of the exciton–polaritons. 相似文献
273.
Yuichi Komazaki Masashi Hiratsuka Yasushi Narita S. Tanaka Tomio Fujita 《Fresenius' Journal of Analytical Chemistry》1999,363(7):686-695
An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH3CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid
chromatograph (HPLC). With this technique, atmospheric HCHO and CH3CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE)
tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected
as the scrubbing solution for collecting HCHO and CH3CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde
(DNPH-CH3CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS
column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH3CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with
a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH3CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones)
of HCHO and CH3CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard
solution of DNPH-HCHO and DNPH-CH3CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%.
Interferences from O3 and NO2 were insignificant in this annular diffusion scrubber method. Both for HCHO and CH3CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method.
Received: 15 July 1998 / Revised: 5 October 1998 / Accepted: 7 October 1998 相似文献
274.
Yuichi Komazaki Masashi Hiratsuka Yasushi Narita S. Tanaka Tomio Fujita 《Analytical and bioanalytical chemistry》1999,363(7):686-695
An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH3CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid chromatograph (HPLC). With this technique, atmospheric HCHO and CH3CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected as the scrubbing solution for collecting HCHO and CH3CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde (DNPH-CH3CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH3CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH3CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones) of HCHO and CH3CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard solution of DNPH-HCHO and DNPH-CH3CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%. Interferences from O3 and NO2 were insignificant in this annular diffusion scrubber method. Both for HCHO and CH3CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method. 相似文献
275.
T Ohkawa T Zenkoh M Tomita N Hosogai K Hemmi H Tanaka H Setoi 《Chemical & pharmaceutical bulletin》1999,47(4):501-510
The present study was undertaken to evaluate whether a novel series of 2,6-diaza-5-oxobicyclo[5.4.0]undeca-1(7),8,10-triene derivatives exhibited antagonistic activity for vasopressin V1 and V2 receptors. Most of these compounds were synthesized and showed a high affinity potential for V2 receptor and low to moderate affinity potential for V1 receptor. The most potent and V2-selective compound, N-[4-[2,6-diaza-6-[2-(4-methylpiperazinyl)-2-oxoethyl] -5- oxobicyclo[5.4.0]undeca-1(7),8,10-trien-2-yl]-carbonyl]pheny l][2-(4- methylphenyl)phenyl]-formamide (11b), exhibited IC50's of 2.9 nM for the V2 receptor and 200 nM for the V1 receptor, respectively. When administered orally to rat, 11b showed an approximately 18-fold increased urine volume in comparison with control rat. 相似文献
276.
Hidetoshi Tomita Fumio Sanda Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2001,39(6):851-859
This article focuses on the structural analysis of polyhydroxyurethane obtained by the reaction of 2,2‐bis[p‐(1,3‐dioxolan‐2‐one‐4‐yl‐methoxy)phenyl]propane with a diamine based on the model reaction. The compounds obtained in the model reaction could be separated into hydroxyurethanes containing primary and secondary alcohol groups by preparative gel permeation chromatography with a recycling technique to determine the structures by 1H NMR, 13C NMR, distortionless enhancement by polarization transfer (DEPT) and C H correlation spectroscopy to obtain hydroxyurethane carrying the primary alcohol structure moiety dominantly. The ratios were independent of the reaction temperature but somewhat dependent on the solvents and amines. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 851–859, 2001 相似文献
277.
278.
The ring‐opening polymerization of (R,S)‐β‐butyrolactone (BL) in bulk was analyzed with respect to the polymer structure of the resulting poly[(R,S)‐3‐hydroxybutanoate)] [P(3HB)] by isolation of the pure form using preparative supercritical CO2 fluid chromatography. It was confirmed that the four‐membered BL was polymerized in bulk by lipase to yield the corresponding cyclic, hydroxy‐ and crotonate‐terminated P(3HB)s. The relative ratios of the three types of polymers depended on the lipase concentration as well as on the monomer conversion. It was also confirmed that both cyclic and linear P(3HB) polymer species were subject to hydrolysis, and inter‐ and intramolecular transesterification by lipase to produce two series of polymers having linear and cyclic structures with higher and lower molecular weight. The formation of the cyclic P(3HB) iss regarded as the characteristic feature of the lipase‐catalyzed polymerization of BL. 相似文献
279.
280.