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991.
C. Osterroht 《Chromatographia》1987,23(6):419-422
Summary A method for the determination of fatty acids of the molecular weight range of propionic to erucic acid is reported. The acids are converted to either p-bromophenacyl-or p-phenylphenacylesters and the esters are separated by HPLC and detected by UV-absorption. Twentytwo esters, including saturated, monoolefinic and polyunsaturated ones were separated within one HPLC-run. The detection limit is about 5 pmol per fatty acid. The application of the method to particulate material is described. 相似文献
992.
A theory is presented for predicting the size of ice crystals which result from steady-state, unidirectional growth within aqueous agar gels. Cellular arrays of adjacent ice crystals were separated by an amorphous water-agar membrane at a composition near the vitrification point. Using this vitrification composition and both a steady-state condition and a minimum free energy criterion, the size of ice crystals was predicted for a given solidification velocity and diffusion condition. It was found, however, that this simple model could not predict the trend towards larger crystal sizes that was observed when the initial agar concentration in the gels increased from 3% to 10% by weight agar. 相似文献
993.
Application of mono (6A-N-ethylenediamine-6A-deoxy) perphenylcarbamoylated β-cyclodextrin (β-CD) bonded stationary phase (CSP) in micro-high performance liquid chromatography (micro-HPLC) and pressurized capillary electrochromatography (p-CEC) was firstly presented. A series of racemic α-amidophosphonates were resolved in reversed- and normal-phase modes on this CSP. The investigated chromatographic parameters include retention factor (k′), separation factor (α) and resolution (Rs) of solutes. In addition, the structural variation of the solutes and the experimental factors affecting chiral separations have been examined, including the percentage of alcohol modifier, the linear velocity (u) of the mobile phase, electrical field strength, etc. Baseline separation was achieved for most of the entities. Hydrophobic interaction, steric effect and π-π interaction contribute to the possible mechanism. Comparative results indicate that higher Rs value up to 3.1 was found in micro-HPLC, higher efficiency up to 29,970 in p-CEC. 相似文献
994.
C. Brenier-Maurel C. Delaurent G. Pages M. -C. Guilhem A. M. Siouffi 《Chromatographia》2002,56(5-6):277-282
Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography
on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology.
The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments,
truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both
separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and
the four flavonoids are separated in less than seven minutes. 相似文献
995.
人尿中异黄酮的高效液相色谱分析 总被引:3,自引:1,他引:3
建立了测定人尿中异黄酮组分(大豆苷原、黄豆黄素、雌马酚、染料木黄酮)含量的反相高效液相色谱法。在尿样中加入黄酮作为内标,异黄酮经酶解后在pH=7.0中性条件下用乙酸乙酯(1∶1)提取,然后用0.02%TFA-M eOH-ACN三元梯度洗脱的方法分离异黄酮。在该条件下,大豆苷原、黄豆黄素、雌马酚、染料木黄酮的检出限分别为12.9 nmol/L、13.9 nmol/L、71.6 nmol/L和11.8 nmol/L;回收率均在89%以上。本方法具有测试步骤简单、准确度高、重现性好等优点,适合大批量样品测定。 相似文献
996.
In a reaction system consisting of FeCl2,tetrathiometallate and cycloalkylthiolate,two Fe4S4 cubane-like cluster compounds were obtained with the following crystallographic data:(PhCH2NMe32[Fe4S4 (SC5H9)4](Ⅰ),monoclinic space group P21/c,a=1.6327(4),6=1.1229(3),c=2.802 5( 10) nm,β=94.63(2)°,Z=4,and R=0.074; (Et4N)2[Fe4S4(SC6H11)4](Ⅱ),tetragonal space group I42m,a=1.16705(9),b=1.167 06(2),c=2.063 26(5) nm,Z=2,Dabs=1.28 g/cm3,and R=0.078 The participation of cy-cloalkylthiolate ligand does not obviously arouse the change of the Fe4S4 core structure.Meanwhile,the influence of the cation on the structural symmetry of the Fe4S4 cluster dianion is also discussed. 相似文献
997.
Synthesis and Structure of Copper(I)Chalcogenolate-2,2′-Bipyridine Complexes [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 and [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 The oligomeric homoleptical copper(I) chalcogenolate compounds [CuS(2,4,6-iPr3C6H2)]x=4,8 and [CuSe(2,4,6-iPr3C6H2)]6 react with 2,2′-bipyridine (Bipy) to yield the tetranuclear complex [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 ( 4 ) and the dinuclear complex [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 ( 5 ). The structures of 4 and 5 were determined by X-ray analysis. In the eight-membered Cu4S4 core of 4 with chair conformation the copper atoms are linked by μ2-bridging selenolate ligands. Only two copper atoms are coordinated by 2,2′bipyridine. The corresponding copper(I) selenolate complex ( 5 ) forms a folded four-membered Cu2Se2 ring with μ2-bridging selenolate ligands. The Cu? Cu distance of 2.52 Å is relatively short. In contrast to the reaction performed with 2,2′-bipyridine, addition of phenantroline to 1 respectively 2 yields a dinuclear complex [CuS(2,4,6-iPr3C6H2)]2(Phen)2 ( 10 ). NMR spectroskopic and cryoscopic measurement of 4 show that this complex dissociates into smaller fragments in solution which undergo rapid exchange reactions. However, corresponding investigations performed on 5 indicate that the solid state structure is maintained in solution. The electrochemical behaviour of 4, 5 and 10 was studied in CH2Cl2 and in any case no reversible redox processes could be observed. 相似文献
998.
Summary In this study a new approach is presented for on-line radiometric detection in reversed phase LC of medium to low polarity
compounds labelled with14C.
The test compounds,14C-carbaryl and14C-parathion, are extracted post-column into a non-water miscible liquid scintillation cocktail. The segmented two-phase system
formed is introduced into the beta-detector without phase separation and collected in a capillary storage tube.
After completion of the LC separation and detection process, the direction of the flow in the storage system is reversed and
the segmented contents of the loop led at lower flow-rates through the beta-detector again. An enhanced signal, corresponding
to the increase in counting time is obtained without measurable peak broadening.
The lowest possible detection limit of the system is 9 counts per peak corresponding to subnanogram quantities of tested pesticides.
Calibration curves are linear over at least 2 orders of magnitude and have the expected theoretical slopes.
The reproducibility of the system is better than 4 % rel. S.D. An application to a recovery study of parathion shows the practical
potential of this technique.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
999.
Summary A computer interactive identification system is proposed which is based on the relationship between retention and molecular
properties such as the size and shape of polycyclic aromatic hydrocarbons (PAHs). This system offers an automatic analytical
process for liquid chromatography, providing a reliable identification of the separated components. The identification can
be further enhanced by the use of multiple detectors such as a multichannel UV detector. The system can be used for optimization
procedures, resulting in a highly automatic complex analytical system. 相似文献
1000.
The thermal reaction between the tris(μ-hydrido)dodecacarbonyltrirhenium (o) cluster and triphenylphosphine or triphenylphosphite results in a trisubstituted rhenium cluster as the major product. The results of an X-ray structural analysis of H3Re2(CO)9(PPh3) are: Mr=1597.57, Monoclinic, P21/n, a=15.598(1), b=9.530(2), c=41.685(3) Å, β=80.60(1)°, V=6113.(1) Å3, Z=4, Dc=1.736 g/cm3, CuKe, λ-1.54056 Å, μ-121.23 cm?1, F(000)=3059.17, room temperature, R=0.049 for 7361 reflections with I≥2.5σ(I). The molecule has a triangular Re2 core coordinated propellerwise by three PPh3 ligands in the molecular plane with virtual C3k symmetry. 相似文献