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961.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
962.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
963.
特征线法在求解非线性液相吸附色谱模型中的应用 总被引:1,自引:0,他引:1
本文应用特征线法求解非线性液相吸附色谱分离过程模型,论述了特征线法的原理和步骤,讨论了时间步长和空间步长对模型数值解的影响,并用色谱分离甘露醇和山梨醇以及分离蔗糖和还原糖的实验进行验证,用特征线法计算的理论流出曲线与实验流出线吻合较好。本文还分折了模型中各个参数的灵敏度,结果表明:吸附等温方程Q=Ci*/(ai+biCi*)中参数ai比参数bi以及总传质系数ki有更高的灵敏度。 相似文献
964.
965.
966.
967.
968.
Simultaneous determination of triterpene saponins in ginseng drugs by high-performance liquid chromatography 总被引:3,自引:0,他引:3
A HPLC method for the simultaneous determination of 11 triterpene saponins with four-type aglycones (protopanaxadiol, protopanaxatriol, ocotillol and oleanolic acid types) in Ginseng drugs was developed and validated. Using a gradient of acetonitrile and 10 mM K-phosphate buffer (pH 5.80) as the mobile phase and UV detection at 196 nm, more than 18 ginsenosides with different aglycones were separated satisfactorily within 60 min. The detection limits (signal/noise> or =3) were 0.1 microg for ginsenosides Rb1, Rc, Rd, Re and Rg1, chikusetsusaponin III, and notoginsenoside R2, 0.2 microg for gisenoside Ro and chikusetsusaponin IVa, 0.3 microg for chikusetsusaponin IV, and 3 microg for majonoside R2. The calibration curve of each saponin had a correlation coefficient close to 1. Intra- and interday precisions were less than 2.1% (n=5) and 3.3% (n=15), respectively. The recovery rates of extraction were in the range of 96.4-102.7% for all ginsenosides. By adopting this method, the determinations of 11 ginsenosides in three Ginseng drugs derived from Panax ginseng, Panax vietnamensis var. fuscidiscus and Panax japonicus (Japan) were achieved. 相似文献
969.
970.
Danielle Giron S. Monnier M. Mutz P. Piechon T. Buser F. Stowasser K. Schulze M. Bellus 《Journal of Thermal Analysis and Calorimetry》2007,89(3):729-743
Adequate very sensitive quantification methods are needed for the development and are also now required for the monitoring
of undesirable solid form(s) as routine tests. The pre-requisite for quantitation are selectivity, sensitivity and most important
the purity of standards and their proper storage, what is a challenge for metastable forms.
Several analytical techniques are available such as X-ray diffraction, spectroscopy, thermal analysis and microcalorimetry.
The different steps of the validation of the analytical methods and problems to be solved are discussed. Examples illustrate
the different techniques and compare their possible advantages and limits. The relative standard deviation of measurements
should allow for checking the homogenization procedure of mixtures for calibration. The validation should be carried out following
ICH guidelines for validation of analytical methods. Comparison of different techniques in adequate concentration range add
confidence in the analytical results. 相似文献