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41.
Quality evaluation of Flos lonicerae through a simultaneous determination of seven saponins by HPLC with ELSD 总被引:9,自引:0,他引:9
A new HPLC coupled with evaporative light scattering detection (ELSD) method has been developed for the simultaneous quantitative determination of seven major saponins, namely macranthoidin B (1), macranthoidin A (2), dipsacoside B (3), hederagenin-28-O-beta-D-glucopyranosyl(6-->1)-O-beta-D-glucopyranosyl ester (4), macranthoside B (5), macranthoside A (6), and hederagenin-3-O-alpha-L-arabinopyranosyl(2-->1)-O-alpha-L-rhamnopyranoside (7) in Flos Lonicerae, a commonly used traditional Chinese medicine (TCM) herb. Simultaneous separation of these seven saponins was achieved on a C18 analytical column. The mobile phase consisted of (A) acetonitrile-acetic acid (95:0.5) and (B) 0.5% aqueous acetic acid using a gradient elution of 29%A at 0-10 min, 29-46%A at 10-25 min and 46%A at 25-30 min. The drift tube temperature of ELSD was set at 106 degrees C, and with the nitrogen flow-rate of 2.6 l/min. All calibration curves showed good linear regression (r2>0.9922) within test ranges. This method showed good reproducibility for the quantification of these seven saponins in Flos Lonicerae with intra- and inter-day variations of less than 3.0% and 6.0%, respectively. The validated method was successfully applied to quantify seven saponins in five sources of Flos Lonicerae, which provides a new basis of overall assessment on quality of Flos Lonicerae. 相似文献
42.
Hu H Qiao M Xie F Fan K Lei H Tan D Bao X Lin H Zong B Zhang X 《The journal of physical chemistry. B》2005,109(11):5186-5192
The desulfurization of thiophene on Raney Ni and rapidly quenched skeletal Ni (RQ Ni) has been studied in ultrahigh vacuum (UHV) by X-ray photoelectron spectroscopy (XPS). The Raney Ni or RQ Ni can be approximated as a hydrogen-preadsorbed polycrystalline Ni-alumina composite. It is found that thiophene molecularly adsorbs on Raney Ni or RQ Ni at 103 K. At 173 K, thiophene on alumina is desorbed, while thiophene in direct contact with the metallic Ni in Raney Ni undergoes C-S bond scission, leading to carbonaceous species most probably in the metallocycle-like configuration and atomic sulfur. On RQ Ni, the temperature for thiophene dissociation is about 100 K higher than that on Raney Ni. The lower reactivity of RQ Ni toward thiophene is tentatively attributed to lattice expansion of Ni crystallites in RQ Ni due to rapid quenching. The existence of alumina and hydrogen may block the further cracking of the metallocycle-like species on Raney Ni and RQ Ni at higher temperatures, which has been the dominant reaction pathway on Ni single crystals. By 473 K, the C 1s peak has disappeared, leaving nickel sulfide on the surface. 相似文献
43.
In the present paper, we describe a microfluidics-based sensing system for nonelectroactive anions under negative separation electric field by mounting a single carbon fiber disk working electrode (WE) in the end part of a poly(dimethylsiloxane) microchannel. In contrast to work in a positive separation electric field described in our previous paper (Anal. Chem. 2004, 76, 6902-6907), here the electrochemical reduction reaction at the WE is not coupled with the separation high-voltage (HV) system, whereas the electrochemical oxidation reaction at the WE is coupled with the separation HV system. The electroactive indicator is the carbon fiber WE itself but not dissolved oxygen. This provides a convenient and sensitive means for the determination of nonelectroactive anions by amperometry. The influences of separation voltage, detection potential, and the distance between the WE and the separation channel outlet on the response of the detector have been investigated. The present detection mode is successfully used to electrochemically detect F-, Cl-, SO4(2-), CH3COO-, H2PO4-. Based on the preliminary results, a detection limit of 2 microM and a dynamic range up to three orders of magnitude for Cl- could be achieved. 相似文献
44.
45.
A piezoelectric response model on the population growth of microorganism is proposed. This model is based on a novel population growth model, which has a more obvious ecological meaning and the fact that the series piezoelectric quartz crystal (SPQC) sensor responses to conductivity changes of the medium during the growth of the microorganism. From the response model four parameters can be obtained including the maximum specific growth rate mu(m), saturated population size N(m), and two constants C and K(1). The influence of the parameters on the response curve is discussed in which the influences of mu(m) and N(m) are more obvious. With the proposed model the quantitative determination of bacteria may be more accurate than the frequency detection time (FDT) method. Then the growth of Escherichia coliform (E. coli) monitored with a SPQC sensor is compared with the simulated growth curve obtained by the proposed model and a good agreement is obtained. 相似文献
46.
Bao Gia Nguyen 《Journal of statistical physics》1987,49(1-2):235-243
A study is made of the gap exponents for percolation processes with the triangle condition in the subcritical region. It is show that the gaps are given by
t
=2 fort=2, 3,. Scaling theory predicts thatP
p
(¦C
0¦S(p))–(p
c
–p) andE
p
(1/¦C
0¦; ¦C
0¦S(p))–(p
c
–p)3, whereS(p) is the typical cluster size. It is found that (p
c
–p)P
p
(|C
0S(p)
1–)(p
c
–p)1–2 and (p
c
–p)3E
p
(1/|C
0|;|C
0|S(p)
1–))(p
c
–p)3–4. 相似文献
47.
Li-Juan Jia Yuan-Yuan Wang Hui Chen Yong-Kui Shan Li-Yi Dai 《Reaction Kinetics and Catalysis Letters》2005,86(2):267-273
Summary The alkylation of benzene with 1-hexene has been investigated in different triethylamine hydrochloride-ferric chloride (Et3NHCl-FeCl3) and triethylamine hydrochloride-aluminium chloride (Et3NHCl-AlCl3) ionic liquids. Both high catalyst activity and monoalkylation selectivity were observed for these two type of ionic liquids.
Systems prepared by modification with HCl in Et3NHCl-FeCl3ionic liquids prove to be very suitable solvents and catalysts for the reaction. When employing Et3NHCl-AlCl3ionic liquids as catalysts, the reaction takes place in biphasic mode with facile catalyst separation and catalyst recycling. 相似文献
48.
Song H Hecimovic S Goate A Hsu FF Bao S Vidavsky I Ramanadham S Turk J 《Journal of the American Society for Mass Spectrometry》2004,15(12):1780-1793
Dysregulation of proteolytic processing of the amyloid precursor protein (APP) contributes to the pathogenesis of Alzheimer's Disease, and the Group VIA phospholipase A(2) (iPLA(2)beta) is the dominant PLA(2) enzyme in the central nervous system and is subject to regulatory proteolytic processing. We have identified novel N-terminal variants of iPLA(2)beta and previously unrecognized proteolysis sites in APP constructs with a C-terminal 6-myc tag by automated identification of signature peptides in LC/MS/MS analyses of proteolytic digests. We have developed a Signature-Discovery (SD) program to characterize protein isoforms by identifying signature peptides that arise from proteolytic processing in vivo. This program analyzes MS/MS data from LC analyses of proteolytic digests of protein mixtures that can include incompletely resolved components in biological samples. This reduces requirements for purification and thereby minimizes artifactual modifications during sample processing. A new algorithm to generate the theoretical signature peptide set and to calculate similarity scores between predicted and observed mass spectra has been tested and optimized with model proteins. The program has been applied to the identification of variants of proteins of biological interest, including APP cleavage products and iPLA(2)beta, and such applications demonstrate the utility of this approach. 相似文献
49.
50.
PU大分子单体水溶液性质 总被引:2,自引:0,他引:2
双亲聚合物一般由亲水和亲油 2种链段构成 ,有嵌段型[1,2 ] 和接枝型[3 ] 2种 ,其中通过大分子单体法合成双亲接枝聚合物备受关注[4] 。如以亲水性大分子单体和亲油性小分子单体共聚 ,大分子单体构成共聚物主链上支链 ,具有较大活动性 ,亲水效能高。采用对氯甲基苯乙烯[5] 或甲基丙烯酰氯[6] 与聚氧化乙烯大分子的一端相反应 ,可得到亲水性大分子单体 ,但其分子量及结构变化有限。本文采用常规条件 ,合成了嵌段式水溶性聚氨酯大分子单体 ,其分子量较大 ,共聚接枝的支链较长。利用该大分子单体具有非离子高分子表面活性剂的性质 ,采用无皂乳… 相似文献