共查询到18条相似文献,搜索用时 737 毫秒
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本工作根据凝胶色谱柱的单分散校准关系和试样的实效关系间的理论联系,建议了一个从一组重均和数均分子量确知的多分散试样的实验谱图,同时订定凝胶色谱柱的分子量校准关系和扩展因子的计算觅数方法。 相似文献
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从对董履和积分方程作矩数分析的结果,建议了两种对凝胶色谱扩展效应作改正的简便方法。引进了改正因子ξ以对实验谱图作改正。当色谱柱是线性柱时,对校准关系作改正可以给出等同的结果。仪器扩展函数可以定义为其中B_M~*为多分散试样分子量的对数与淋出体积间实际关系的斜率。 相似文献
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Hamielec双因子觅数法曾广泛应用于多分散标样校准尺寸排除色谱(SEC)柱.其后,有人将它改进为单因子觅数法,他们一般只使用了一个已知两种标定量(_n和_w或_η)的样品.在已知某一种标定量的多个多分散试样的校准工作中,有的为前述方法在非线性校准上的扩展,仍采用试凑法逼近目标函数;Szewczyk则利用与标定量对应的平均保留体积的概念,提出了一种较为有效的方法. 相似文献
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采用凝胶色谱与多角激光光散射联用的方法,测定了一系列不同分子量的聚乙二醇(PEG)和聚氧化乙烯(PEO)在色谱柱中的扩展效应.扩展因子随PEG/PEO分子量的增加而增大,经扩展效应改正后得到了样品的准确分子量和分子量分布.同时建立了PEO的Z均回转半径Rgz与重均分子量Mw之间的单分散标度关系:Rgz=0.0272 Mw0.56,结果表明,长链PEO在水溶液中由于排除体积效应采取溶胀的无规线团构象. 相似文献
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自动粘度计作为测定分子尺寸的手段与示差际光器联用于凝胶色谱检测器时,将大大扩大其应用范围,如测定粘度常数k、α与色谱柱分离和扩展同时校准,已成为测定聚合物长链支化的有力手段。联机的基本原理比较简单,如图1所示。 相似文献
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With the aid of the theoretical relationship between the calibration relation of a SEC column for the monodisperse polymer species under ideal working condition and the effective relations between the molecular weight and the elution volume for characterized polymer samples, a computational procedure for simultaneous calibration of molecular weight separation and column dispersion is proposed. From the experimental chromatograms of narrow MWD polystyrene standards and broad MWD 1,2-polybutadiene fractions the spreading factors of a SEC column was deduced by the proposed method. The variation of the spreading factor with the elution volume is independent upon the polymer sample used. 相似文献
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Monte Carlo simulations were conducted to estimate the elution curve of size exclusion chromatography (SEC). The present simulation can be applied to various types of branched polymers, as long as the kinetic mechanism of nonlinear polymer formation is given. We considered two types of detector systems, (1) a detector that measures the polymer concentration in the elution volume to determine the calibrated molecular weights, such as by using the differential refractive index detector (RI), and (2) a detector that determines the weight‐average molecular weight of polymers within the elution volume directly, such as a light scattering photometer (LS). For polydisperse star polymers, both detector systems tend to give a reasonable estimate of the true molecular weight distribution (MWD). On the other hand, for comb‐branched polymers, the RI detector underestimates the molecular weight of branched polymers significantly. The LS detector system improves the measured MWD, but still is not exact. The present simulation technique promises to establish various types of complicated reaction mechanisms for nonlinear polymer formation by using the SEC data quantitatively. In addition, the present technique could be used to reinvestigate a large amount of SEC data obtained up to the present to estimate the true MWD. 相似文献
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The elution curves of size exclusion chromatography (SEC) for branched polymers formed through free‐radical polymerization that involves chain transfer to polymer were theoretically investigated by using a Monte Carlo method. We considered two types of measured molecular weight distribution (MWD), (1) the calibrated MWD relative to standard linear polymers, and (2) the MWD obtained by using a light scattering photometer (LS) in which the weight‐average molecular weight of polymers within the elution volume is determined directly. It was found that the calibrated MWD clearly underestimates the high molecular weight tail, and the measured distributions are narrower than the true MWD. On the other hand, the present simulation results showed that the LS method gives reasonable estimates of the true MWDs. The mean square radius of gyration of the polymer molecules having the same molecular weight was also investigated. The radii of gyration showed clear deviation from the Zimm‐Stockmayer equation[1] because of the non‐random nature of branched structure and the difference in the primary chain length distribution. 相似文献
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Using the extension of the concept of universal calibration parameter, yielding a relation between the hydrodynamic volume of molecules and the elution volume in size exclusion chromatography (SEC), to retention coefficients in ultrafiltration (UF), we propose a direct calibration of UF membranes against chromatography columns. Plotting the retention coefficient by one given UF membrane of a series of probe molecules versus their elution volume in SEC chromatography provides a calibration curve for this membrane. For a wide range of retentions, such calibration can be directly used to predict the retention of any molecule: one only needs to measure its exclusion volume by the SEC column, and read the retention by the calibrated membrane on the calibration curves. 相似文献
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《液相色谱法及相关技术杂志》2012,35(8):1537-1544
Abstract The mixture of methylene chloride/hexafluoroisopropanol (70/30, v/v) is an excellent polyester solvent, but its low boiling point causes unstable flow when it is used for size exclusion chromatography (SEC). In high-performance SEC experiments, retention time is normally used to measure elution volume; however, unstable flow makes it difficult to calibrate an SEC column set or calculate molecular weight parameters from a chromatogram. We have devised a simple and inexpensive method to compensate for the effect of unstable flow in SEC calculations. A calibration marker injected along with each sample is used to indicate flow-rate variations. The ratio of the sample retention time to the marker retention time is invariant to flow-rate changes and is used in place of retention time as a measure of elution volume in the universal calibration technique. Calibrating a column set and analyzing chromatograms by this method result in a large improvement in the accuracy and precision of calculated molecular weight parameters. 相似文献
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The effect of deuterated solvents in size-exclusion chromatography (SEC) was studied by comparing intrinsic viscosity measurements, SEC calibration curves, and column efficiency using water-soluble polymers. For aqueous SEC, the use of deuterium oxide slightly increases the SEC elution volume. To verify that adsorption onto the packing was absent, data from exclusion experiments were compared at 35 and 50 degrees C. Our results indicate that adsorption is not occurring for pullulan or polyethylene glycol (PEG)/poly(ethylene oxide) (PEO); for the latter, however, the elution volume increased using both D2O and H2O, indicative of slight hydrodynamic volume contraction of PEG/PEO at higher temperatures. A moderate increase in band broadening (moderate decrease in column efficiency) was observed using D2O. Finally, the effects of chloroform versus deuterated chloroform were evaluated, but no hydrodynamic volume changes were observed. 相似文献
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The molecular weight separation and column dispersion for a number of SEC columns packedwith various packing materials were calibrated simultaneously using narrow MWD polystyrene stan-dards as probe. The molecular weight dependence of the spreading factor is closely related to thesurface structure in the pore of packings. 相似文献