Separation Mechanisms in Gel Permeation Chromatography

Abstract

This paper presents flow rate studies, vacancy chromatography, and a static mixing experiment. Data obtained on an unpacked column (a straight tube) and on a column packed with nonporous glass beads are also reported. The results reveal that peak dispersion in GPC arises mainly from lateral diffusion in the stationary phase (permeation in and out of the porous substrate) and from lateral diffusion in the mobile phase. GPC peak separation is mainly dominated by the process of steric exclusion. Pore size distribution data obtained on Bio-Rad porous glass are shown to illustrate the preference of random coil theories over theories of the equivalent sphere in the interpretation of steric exclusion of flexible polymers. The data are discussed in terms of Herman's diffusion theory and Cassasa's exclusion theory.     

Fast Gel Permeation Chromatography Using Large Gel Particles

Abstract

In two previous papers (1,2), we reported the effect of several operational parameters on separations by gel permeation chromatography (GPC). These studies included the effects of (a) solvent flow rate, (b) sample concentration, (c) sample molecular weight, (d) particle size, and (e) operating temperature. In this present study, we used extremely large particles (200–300 μ diameter) at flow rates up to 10 ml/min. This was done to magnify solute diffusion effects in hope of gaining a better understanding of the permeation process. By using the relatively large particles, interstitial spaces between particles will be wider and the gel pores deeper than with particles normally used (less than 75 μ) in GPC.     

The Overload Effect in Gel Permeation Chromatography

Abstract

Overload phenomena in GPC are investigated with samples of narrow polystyrenes and short but efficient columns packed with Styragel. Viscous fingering is shown to be a leading cause of peak skewing and broadening. A correlation is proposed to define a safe operating range in terms of sample concentration, volume, and the average intrinsic viscosity of the solute polymer.     

Gel Permeation Chromatography with High Loads

Abstract

High loads on GPC columns usually lead to poor efficiency because of steep viscosity gradients. A great difference in density between solution and solvent can also cause excessive band broadening. However, under certain conditions good separations are achieved with loads of 150 mg/100 cc column volume and higher. Two mechanisms are proposed to explain this phenomenon. Secondary exclusion is caused by obstruction of pores to larger molecules by the more rapidly diffusing small molecules. It takes place predominantly with molecules of less than 2000 molecular weight in small pore gels. Incompatibility is caused by repulsive interaction between solute molecules and the polystyrene gel. It is observed with solutes which are chemically quite different from polystyrene, e.g., with polyvinyl acetate, and in a low to intermediate molecular weight range.     

Gel Permeation Chromatography and Thermodynamic Equilibrium

Abstract

Although gel permeation chromatography is firmly established as a technique for investigating heterogeneity in synthetic polymers, the character of the chromatographic process-whether it is dominated by diffusion, by flow effects, or by an equilibrium partitioning of polymer between the mobile phase and the micropores in the column packing-is still disputed. General chromatographic theory supports the idea that under ordinary experimental conditions the equilibrium distribution of a solute determines the position of its elution peak in the chromatogram. Statistical mechanical calculations of distribution coefficients for linear and branched polymer chains and idealized pores of simple geometry lead to predictions in good accord with some experimental findings.     

Fractionation of Residuals by Gel Permeation Chromatography

Abstract

Gel permeation chromatography has been effectively used for the fraction-ation of residuals. The preparative-scale gel permeation chromatograph employed for these studies is described along with selected operating parameters. The instrument has been used to fractionate a shale oil residue, 50% reduced crude, and 25% reduced crude, into fairly narrow molecular weight fractions. The individual cuts from each residual have been analyzed and the elemental distribution established. The trends of heteroatom distribution, i.e., nitrogen, sulfur, nickel, and vanadium, as a function of molecular weight for the various residuals are discussed.     

Composition of Butadiene-Styrene Copolymers by Gel Permeation Chromatography

Abstract

An ultraviolet detector was added to the GPC making it possible to determine both molecular weight distribution and composition of butadiene-styrene copolymers as a function of molecular weight. After calibration, several types of commercial and experimental copolymers were analyzed. SBR was found to have a very uniform composition over most of the range of molecular weight. However, the styrene content decreased at the high end of the distribution. Representative samples of anionically polymerized copolymers were also examined. In general, the composition of these polymers varied more than SBR. Usually, the styrene content was high at low molecular weight and decreased as molecular weight increased. Several experimental copolymers that were first metalated and then grafted with styrene were studied. Incomplete grafting as well as the presence of low molecular weight homopolystyrene was readily detected. This appears to be a particularly sensitive method for studying composition of copolymers.     

Characterization of Crude Oils by Gel Permeation Chromatography

Abstract

The classical method of dividing crude oil into narrow molecular-weight cuts—distillation—is not practical in the high-boiling region. Thus, gel permeation chromatography was evaluated as a technique for characterizing the high-molecular-weight portion of crude oils. Crude oils, stripped to 180[ddot]C, were separated in a dual-column GPC system. The fractions obtained provided information concerning the amounts of material with molecular weights between 400 and 3000. Gross estimates were made of the proportion of ring and nonrmg carbons in these fractions. The latter estimates were obtained by relating molecular weights determined on the fractions to a calibration plot made up from data on model compounds.     

A Computer Simulation of Linear Gel Permeation Chromatography

Abstract

A phenomenological model based on a set of partial differential equations and boundary conditions is proposed for chromatography and, in particular, for gel permeation chromatography. The intractable boundary value problem, which does not have a closed form solution, was handled through the use of numerical methods employing a very large and very fast computer (IBM 360/195). The chromatograms generated by the computer simulator were compared with experimental chromatograms of various molecular weight polymers. The computer generated overlay plots of the simulated and experimental chromatograms showed good agreement (the two plots almost superimposed). The effect of other parameters on the chromatogram, i.e., flow rate, stationary phase bead size, solute diffusion coefficient in the stationary and mobile phases, and the partition coefficient were also investigated.     

常温凝胶色谱仪的使用及维护体会

介绍了常温凝胶色谱仪日常使用中常见的故障,结合自己的工作经验提出了一些日常维护的体会。分别从贮液系统、运输系统、进样系统、分离系统以及检测系统5个方面进行了总结。我们在测试工作中正确使用仪器,尽量避免仪器或耗材的损耗不但能节约测试成本,还能延长仪器使用寿命。     

非正品聚烯烃的鉴别-凝胶渗透色谱方法

采用凝胶渗透色谱(GPC)表征非正品聚烯烃分子质量及其分布的方法。研究表明利用GPC法和熔体流动速率方法,可有效判断聚烯烃料的品质等级。     

Estolide Molecular Weight Distribution via Gel Permeation Chromatography

Using the universal calibration and the Mark-Houwink equation (MHE) (), three batches of oleic estolide acids and their corresponding 2-ethylhexyl esters were characterized using gel permeation chromatography (GPC). The MHE parameters in tetrahydrofuran (THF) at 40 °C were determined (for acids: α = 0.442 ± 0.003 and log₁₀K =2.505 ± 0.007, for esters: α =0.531 ± 0.006 and log₁₀K =2.794 ± 0.018). The fits of the GPC chromatograms yielded also the oligomeric composition of the estolides, which can be used to calculate the estolide number (EN) of an estolide mixture, and other molecular-weight distribution parameters, such as number-average molecular weight (M_n ), weight-average molecular weight (M_w ), and dispersity (Ð). Using the Deming line fit, we concluded that the GPC should be expected to be approximately three times more sensitive than the currently used methods for determination of EN values.     

凝胶渗透色谱研究水性聚氨酯乳液

通过凝胶渗透色谱研究了不同加料方法、不同扩链剂、不同聚酯对乳液分子量的影响;结果表明：不同扩链剂合成的乳液数均分子量的次序为：BD/DEGT1136>CMA-1044>MX-785>CMA-44。     

凝胶排阻色谱法测定酚醛树脂中的游离苯酚

利用凝胶排阻色谱法进行酚醛树脂中游离苯酚的测定,并与液相色谱法和气相色谱法进行对比。结果表明,凝胶排阻色谱法可以准确地测定酚醛树脂中游离苯酚含量,但不能有效地测定酚醛树脂中游离对叔丁基苯酚、对特辛基苯酚和间苯二酚含量。     

凝胶渗透色谱法测定聚丙烯腈分子质量时的影响因素

通过使用凝胶渗透色谱法(GPC)对聚丙烯腈相对分子质量进行测试,详细研究了样品质量浓度和进样体积对测试结果的影响,并对GPC谱图中不同溶剂峰和异常峰的产生原因进行了分析.结果表明:样品质量浓度增加、进样体积增大导致GPC测得的聚丙烯腈重均分子质量、数均分子质量及分子质量分布减小;溶剂峰与异常峰的出现对最终测试结果影响不大.     

A Comparison of Gel Permeation Chromatography and Liquid Chromatography for Epoxy Resin Analysis

Gel permeation chromatography and liquid Chromatography are used for analyzing various epoxy resins. The chromatograms are compared with related information available from each. Because the separation is based on different principles, each method gives unique and different information about the same sample. For a complete analysis of epoxy resins, both techniques seem to be required.     

Gel Permeation Chromatography Calibration. I. Use of Calibration Curves Based on Polystyrene in THF and Integral Distribution Curves of Elution Volume to Generate Calibration Curves for Polymers in 2,2,2-Trifluoroethanol

Abstract

A general method is proposed for obtaining gel permeation chromato-graphic (GPC) molecular weight (MW) and hydrodynamic volume (HDV) calibration curves for polymer-solvent systems where primary polymer standards are unavailable. The method is demonstrated by using a HDV calibration curve based on polystyrene in tetrahydrofuran (THF), in conjunction with integral distribution curves of elution volume for poly(methyl methacrylate) (PMMA) in THF and in 2,2,2-tri-fluoroethanol (TFE) for the generation of a HDV calibration curve in TFE. Transformation methods for generating secondary MW calibration curves from HDV calibration curves are discussed and applied to PMMA in THF and TFE, and to poly(trimethylene oxide), poly(vinyl acetate), and certain polyamides in TFE. The utility and reliability of the secondary calibration curves are demonstrated by comparing MW average and intrinsic viscosites obtained by GPC and by the classical methods. Molecular structural differences among th polyamide samples associated with the distribution of short- and long-chain branches are discussed in relation to their secondary calibration curves.     

凝胶渗透色谱－液相色谱－串联质谱法测定水产品中性激素

建立水产品中性激素的凝胶渗透色谱净化－超高效液相色谱－串联质谱分析方法。采用乙酸乙酯提取样品,经GPC净化后, LC－MS／MS测定,外标法定量。流动相为乙腈和0．1％甲酸水溶液,梯度洗脱,电喷雾正离子多反应模式监测。3种性激素在0．5～20．0μg／L线性范围内,相关系数大于0．998,定量限为0．3μg／kg,回收率为88．6％～96．4％,相对标准偏差为1．84％～6．24％。本方法灵敏度高、重现性好,适用于水产品中性激素的测定。