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11.
The phenomenon known as "matrix-induced enhancement effect" is not only observed in the analysis of pesticides in food, but also in Chinese herbs. Several approaches have been proposed to overcome the matrix-induced effect, but each method has serious limitations. Compared with standard calibration methods, the procedure with adding analyte protectants offers a more convenient and effective route to solve the problem. In the current study, we have analyzed 195 types of pesticides in Chinese herbs by gas chromatography-mass spectrometry (GC-MS), and the compounds that are susceptible to matrix effect were picked up and confirmed. In addition, several analyte protectants were evaluated and the most effective combination was determined. D-ribonic acid-γ-lactone (2 mg/ml) and D-sorbitol (1 mg/ml) were shown to be the best analyte protectants for the analysis of most pesticides. 相似文献
12.
Shadow images and observed luminosity of the Bardeen black hole surrounded by different accretions 下载免费PDF全文
In this paper, by exploring photon motion in the region near a Bardeen black hole, we studied the shadow and observed properties of the black hole surrounded by various accretion models. We analyzed the changes in shadow imaging and observed luminosity when the relevant physical parameters are changed. For the different spherical accretion backgrounds, we find that the radius of shadow and the position of the photon sphere do not change, but the observed intensity of shadow in the infalling accretion model is significantly lower than that in the static case. We also studied the contribution of the photon rings, lensing rings and direct emission to the total observed flux when the black hole is surrounded by an optically thin disk accretion. Under the different forms of the emission modes, the results show that the observed brightness is mainly determined by direct emission, while the lensing rings will provide a small part of the observed flux, and the flux provided by the photon ring is negligible. By comparing our results with the Schwarzschild spacetime, we find that the existence or change of relevant status parameters will greatly affect the shape and observed intensity of the black hole shadow. These results support the theory that the change of state parameter will affect the spacetime structure, thus affecting the observed features of black hole shadows. 相似文献
13.
Steady thermocapillary-buoyant convection in a shallow annular pool. Part 1: Single layer fluid 总被引:1,自引:0,他引:1
You-Rong Li · Shuang-Cheng Wang · Chuan-Mei Wu College of Power Engineering Chongqing University Chongqing China Key Laboratory of Low-grade Energy Utilization Technologies Systems Ministry of Education China 《Acta Mechanica Sinica》2011,27(3):360-370
This paper examines the steady thermocapillarybuoyant convection in a shallow annular pool subjected to a radial temperature gradient. A matched asymptotic theory is used to obtain the asymptotic solutions of the flow and thermal fields in the case of small aspect ratios,which is defined as the ratio of the layer thickness to the gap width. The flow domain is divided into the core region away from the cylinder walls and two end regions near each cylinder wall. Asymptotic solutions are obtained in the core region by solving the core and end flows separately and then joining them through matched asymptotic expansions. For the system of silicon melt,the asymptotic solutions are compared with the results of numerical simulations. It is found that the two kinds of solutions have a good agreement in the core region for a small aspect ratio. With the increase of aspect ratio,the applicability of the present asymptotic solutions decreases gradually. 相似文献
14.
Lu Zhang Ming-Hua Li Jing Tian Meng Yin Xian-Long Cheng Feng Wei Shuang-Cheng Ma 《Journal of separation science》2022,45(7):1297-1304
Pulsatillae Radix, the root of Pulsatilla chinensis (Bge.) Regel, is recorded in the Pharmacopoeia of the People's Republic of China and has been widely used for its pharmacological activities, such as anti-inflammatory, antioxidant, antibacterial, antitumor, and cardiovascular benefits. However, there are several look-alike species that can be marketed as Pulsatillae Radix. To distinguish P. chinensis (Bge.) Regel from its look-alikes, viz. Pulsatilla cernua (Thunb.) Bercht et Opiz., Pulsatilla dahurica (Fisch.) Spreng., Anemone tomeutosa (Maxim.) Pei., and Rhaponticum uniflorum (L.) DC, we used ultra high performance liquid chromatography with time-of-flight mass spectrometry combined with principal component analysis to compare their chemical compositions. Four ions, a (RT 8.98 min, m/z 1381.6671), b (RT 10.64 min, m/z 1219.6143), c (RT 11.52 min, m/z 1217.5978), and d (RT 13.6 min, m/z 749.4463), from P. chinensis (Bge.) Regel were identified as potential chemical markers to distinguish it from look-alike species using an unsupervised statistical model combined with orthogonal partial least-squares discriminant analysis. The results of this study provide an effective method for identifying and distinguishing P. chinensis (Bge.) Regel from similar plants. 相似文献
15.
Ma LY Ma SC Wei F Lin RC But PP Lee SH Lee SF 《Chemical & pharmaceutical bulletin》2003,51(11):1264-1267
Five compounds have been isolated from the dried whole plants of Selaginella uncinata, two of them were new chromone glycosides, 5-hydroxy-2,6,8-trimethylchromone 7-O-beta-D-glucopyranoside (uncinoside A) and 5-acetoxyl-2,6,8-trimethylchromone 7-O-beta-D-glucopyranoside (uncinoside B). Their structures were elucidated by spectroscopic methods including one- and two-dimensional NMR techniques. The other three compounds were identified as 8-methyl eugenitol, amentoflavone and hinokiflavone. Uncinoside A and B showed potent antiviral activities against respiratory syncytial virus (RSV) with IC(50) value of 6.9 and 1.3 microg/ml, moderate antiviral activities against parainfluenza type 3 virus (PIV 3) with IC(50) value of 13.8 and 20.8 microg/ml, respectively. 相似文献
16.
Zhi-Lin Luan Fei Qiao Wen-Yu Zhao Wen-Hua Ming Zhen-Long Yu Jie Liu Sheng-Yun Dai Shuang-Hui Jiang Chao-Jie Lian Cheng-Peng Sun Bao-Jing Zhang Jian Zheng Shuang-Cheng Ma Xiao-Chi Ma 《中国化学》2021,(5):1288-1296
Main observation and conclusion
The investigation of Morinda officinalis led to the isolation of twelve compounds (1-12),including three new iridoid glycosides ... 相似文献
17.
五叶木通中一个新的三萜成分 总被引:1,自引:0,他引:1
对五叶木通藤茎进行了较为系统的研究, 从其体积分数为80%的乙醇提取物的正丁醇部分分离得到3个三萜成分, 通过理化性质和波谱分析鉴定为: 3α,24-二羟基-30-去甲齐墩果烷-12,20(29)-双烯-28-酸(Ⅰ); 3α,24,29-三羟基齐墩果烷-12-烯-28-酸(Ⅱ); 2α,3β,23-三羟基齐墩果烷-12-烯-28-酸(Ⅲ). 其中化合物Ⅱ为新化合物, 命名为木通茎酸(Quinatic stem acid). 相似文献
18.
Wei F Ma LY Jin WT Ma SC Han GZ Khan IA Lin RC 《Chemical & pharmaceutical bulletin》2004,52(10):1246-1248
Phytochemical study of the ethanol extract of the seeds of Aesculus chinensis led to the isolation of a new triterpenoid saponin (6), together with five known triterpenoid saponins (1-5). The structure of the new compound was elucidated on the basis of spectral data to be 21,28-di-O-acetylprotoaescigenin-3-O-[beta-D-glucopyranosyl(1-2)][beta-D-glucopyranosyl(1-4)]-beta-D-glucopyranosiduronic acid (aesculiside A, 6). The antiinflammatory activities of the four main saponins (1-4) were compared with those of total saponin extracts, and single saponins showed more potent activity than total saponin extracts in mice. 相似文献
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20.
Cheng XL Ma SC Wei F Wang GL Xiao XY Lin RC 《Chemical & pharmaceutical bulletin》2007,55(9):1390-1392
A new sesquiterpene, neolindenenonelactone (1), was first isolated from the dried roots of Lindera aggregata (SIMS) KOSTERM., along with four known compounds, linderane (2), isolinderalactone (3), linderalactone (4), and 8-hydroxylindestenolide (5). Their chemical structures were elucidated using spectral analysis of fast atom bombardment mass spectroscopy, one-dimensional nuclear magnetic resonance spectroscopy and two-dimensional-nuclear magnetic resonance spectroscopy including (1)H-NMR, (13)C-NMR, distortionless enhancement by polarization transfer, heteronuclear multiple-bond coherence, and single-crystal X-ray diffraction techniques. 相似文献