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排序方式: 共有475条查询结果,搜索用时 9 毫秒
41.
Ali Reza Fakhari Saeed Nojavan Samad Nejad Ebrahimi Christopher John Evenhuis 《Journal of separation science》2010,33(14):2153-2159
This study investigated the use of ultrasound‐assisted extraction to improve the extraction efficiency of morphine, codeine and thebaine from the papaver plants. Extraction conditions such as type of solvent, temperature, duration, frequency and power level of ultrasonic were optimized and the influences of different parameters on resolution of alkaloids in CE were studied. The optimized condition for CE separation includes a sodium phosphate buffer (100 mM, pH 3.0) containing 5 mM α‐CD. The optimized extraction conditions for ultrasound‐assisted extraction was an extraction time of 1 h, an ultrasonic frequency of 60 kHz with water–methanol (80:20) at 40°C as the extraction solvent. The LOD for alkaloids was found to be 0.1 μg/mL at a signal‐to‐noise ratio of 3:1. The RSDs for peak areas were in the range of 1.4–4.4%. The amounts of opium alkaloids (mg/100 g dried sample) in four Iranian papaver plants were found to be in the range of 7.8–8.7 (morphine), 5.5–9.5 (codeine) and 1.4–10.4 (thebaine). It should be emphasized that no cleanup of the filtered extract was required; hence, direct determination after extraction drastically simplifies the analytical process. 相似文献
42.
利用阴离子交换色谱柱及紫外-可见光检测器建立的离子色谱分析方法对植物及土壤中乙二胺二琥珀酸([S,S′]-ethylenediaminedisuccinic acid,EDDS)金属(Fe(III)、Pb、Cu、Zn和Mn)复合物进行了分析,并用电喷雾质谱对其进行了确认。实验选用戴安IonPac AS11-HC阴离子交换色谱柱(250 mm×4.2 mm,5 μm)及保护柱,以60 mmol/L硝酸铵溶液(pH 6.5)为洗脱液,在1.0 mL/min流速下进行等度洗脱,检测波长为260 nm。金属-EDDS复合物的质谱鉴定采用选择离子扫描模式。结果表明,该方法可以用于Fe(III)-、Pb-、Cu-EDDS复合物的分离测定,三者的检出限分别是0.38,0.54和0.18 μmol/L,回收率分别是99.6%,100.6%和97.5%。该方法操作简单、灵敏,适合于植物样品及土壤样品中含有的Fe(III)-、Cu-和Pb-EDDS复合物的单独或同时分析鉴定。 相似文献
43.
R. Otto P. Hecht H. Ulrich H. Hāntzschel 《Isotopes in environmental and health studies》2013,49(4):120-123
Bei technischen Tracerexperimenten bereitet die Markierung von Gasphasen Schwierigkeiten, wenn man auf Außenwandmessungen angewiesen ist, da die Auswahl an geeigneten Radionukliden bzw. radioaktiv markierten Verbindungen dann sehr beschrānkt ist. Eine gute Ergänzung des Radionuklidangebotes für den genannten Zweck bietet 133mXe, Halbwertszeit 2,3 d, Eγ = 0,23 MeV (16%). 133mXe erhält man mit guten Ausbeuten bei einer Reaktoraktivierung von natürlichem Xenon. Die Sälligungsaktivität fär 133mXe beträgt bei einem Fluß von 5,0 μ 1013 n/cm2s 48,5 mCi/cm3 Xenon (unter Normalbedingungen). An Veweilzeitmessungen von Gasphasen in technischen Anlagen werden die Einsatzmöglichkeiten des 133mXe dargestellt. 相似文献
44.
Nikolaos Mantzos Anastasia Karakitsou Ioannis Zioris Eleni Leneti 《International journal of environmental analytical chemistry》2013,93(15):1566-1584
QuEChERS and solid phase extraction (SPE) methods were applied for determining four herbicides (metazachlor, oxyfluorfen, quizalofop-p-ethyl, quinmerac) and one insecticide (α(±)-cypermethrin) in runoff water, soil, sunflower and oilseed rape plant matrices. Determination was performed using gas chromatography mass spectrometry (GC-MS), whereas high-pressure liquid chromatography mass spectrometry (HPLC-MS) was used for quinmerac. In all substrates linearity was evaluated using matrix-matched calibration samples at five concentration levels (50–1000 ng L?1 for water, 5–500 μg kg?1 for soil and 2.5–500 μg kg?1 for sunflower or oilseed rape plant). Correlation coefficient was higher than 0.992 for all pesticides in all substrates. Acceptable mean recovery values were obtained for all pesticides in water (65.4–108.8%), soil (70.0–110.0%) and plant (66.1–118.6%), with intra- and inter-day RSD% below 20%. LODs were in the range of 0.250–26.6 ng L?1 for water, 0.10–1.8 μg kg?1 for soil and 0.15–2.0 μg kg?1 for plants. The methods can be efficiently applied for field dissipation studies of the pesticides in energy crop cultivations. 相似文献
45.
An overview of analytical methodologies for the determination of antibiotics in environmental waters 总被引:3,自引:0,他引:3
The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes. 相似文献
46.
Zhaoming Liu Pei Qiu Jing Li Guangying Chen Yan Chen Hongju Liu Zhigang She 《Tetrahedron》2018,74(7):746-751
A pair of novel 2,3-diaryl indone derivatives (+)- and (?)-ascomindone D [(+)-1 and (?)-1, respectively], as well as two new prenylated polyketides ascomfurans C (2) and ascomarugosin A (3) were obtained from the culture of a mangrove endophytic fungus Ascomycota sp. SK2YWS-L together with three known compounds (4–6). The enantiomers (+)-1 and (?)-1 were purified through chiral HPLC separation, which represented the first example of resolving 2,3-diaryl indone atropisomers in natural products. The structures of the new compounds were determined on the basis of interpretation of spectroscopic data including X-ray diffractions and the absolute configurations of (+)-1 and (?)-1 were elucidated by ECD calculations. The biosynthesis pathway was proposed. In the anti-inflammatory assay, (+)-1 and (?)-1 exhibited potential anti-inflammatory effects by inhibiting against the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced RAW 246.7 mouse macrophages with the IC50 values of 17.0 and 17.1 μM, respectively. 相似文献
47.
本文研究脉冲喷洒杀虫剂的植物病害模型.考虑在传染率随时间周期变化和森林树木总数保持不变的条件下,讨论具有垂直传播的一类具有单个种群的脉冲喷洒农药的SIRS模型,根据单值算子和Bohl-Brouaser不动点理论证明了无病周期解存在性,并且利用单值矩阵,Floquet理论得到其基本再生数并且给出了其无病周期解局部渐近稳定的条件. 相似文献
48.
混凝土搅拌站的选址问题研究 总被引:2,自引:0,他引:2
混凝土搅拌站的选址,在施工中占有十分重要的地位.针对混凝土需求随时间不规则变化的情况以及混凝土有效期短等特点,提出了混凝土需求不规则变化的选址模型.该模型把选址与各个时间段的资源配置结合起来确定混凝土搅拌站的位置,在保证需求最大限度得到满足的同时,使选址能够兼顾到尽可能多的需求点,最大化搅拌站的利润.应用该模型和算法成功地解决了一个实际问题,算例验证了模型和算法的有效性. 相似文献
49.
The motivations to realize nuclear breeder reactors are developed in the present context of a strong growth in electronuclear power stations in many countries, using mostly moderated and water cooled reactors.The past studies can be of a substantial profit in France and, to a lesser degree, in other countries of the EU. However, to use fully the 238 uranium isotope, the materials for these breeders must withstand much harder radiation than those for water reactors. The power densities and thermal gradients will also be much more intense. The mechanical stresses, both static and dynamic, will be large and will act on materials with altered mechanical properties. Fuel elements will have to be produced with materials already irradiated several times and therefore showing such alterations.A field of studies concerning materials and their mechanical behavior in new and severe conditions is sketched here, both in construction and working conditions, together with proposed necessary instrumentation and research orientations. 相似文献
50.
Antonio F. Aguilera-Carbo Christopher Augur Lilia A. Prado-Barragan Cristóbal N. Aguilar Ernesto Favela-Torres 《Chemical Papers》2008,62(4):440-444
Ellagic acid (EA) was quantified by reversed-phase high-performance liquid chromatography (RPHPLC) coupled with photodiode
array detection (DAD) in five fine-powdered plants collected from the semiarid region of Mexico. Samples analysed included
Jatropha dioica branches (Dragon’s blood), Euphorbia antisyphyllitica branches (Candelilla), Turnera diffusa Willd leaves (Damiana), Flourensia cernua leaves (hojasén) and Punica granatum husk (pomegranate) at two maturity stages (“turning” or intermediate and maturated fruit, considered as positive controls).
The results demonstrated high EA concentrations in all tested samples which are novel sources of this natural antioxidant.
The method developed for the EA analysis is fast and it showed an excellent linearity range, repeatability, intra-and inter-day
precision and accuracy with respect to the methods reported for the EA analysis. 相似文献