Concentration effects and thermodynamic nonideality in gel chromatography

The dependence of the elution volume V_e on the concentration of injected polymer c in gel chromatography is presented for several systems including poly(styrene) and poly(methyl methacrylate) in a number of pure solvents with SiO₂-based gels. The linear dependence of V_e on c and K_av on c (where K_av is the distribution coefficient) is confirmed in the region of very low concentration. The slopes k of the straight lines increase with increasing relative molecular masses M of the polymer injected and with increasing thermodynamic nonideality of the system (as expressed by the second virial coefficient A₂). The significance of the slope of the GPC calibration curve for meaningful comparison of the concentration effects in various chromatographic systems is pointed out. A recently found correlation between k and (A₂M)γ is confirmed with a γ value of about 0.8. A possible theoretical explanation for the deviation of γ from unity is discussed. Finally, the influence of both the polymer concentration and the thermodynamic quality of the eluent on the resolution index of the chromatographic system is evaluated with the conclusion that thermodynamically poor solvents should be preferred for preparative GPC separations with very high loads.     

Polymer-Gel Interactions in GPC with Organic Eluents

Abstract

The displacement of hydrodynamic volume universal calibration curves to high retention volumes for some polymer-solvent systems is explained in terms of a network-limited separation consisting of a steric exclusion mechanism and a second mechanism resulting from polymer-gel interactions. This treatment is consistent with a thermodynamic interpretation of GPC separations in which the distribution coefficient (≥ 1.0) for polymer-gel interactions is determined by an enthalpy change for polymer partition or polymer adsorption in the porous packing. Examples of the application of the network-limited treatment to experimental data obtained with crosslinked polystyrene gels and inorganic packings are presented. Network-limited separations in which the distribution coefficient for polymergel interactions is less than unity correspond to partial exclusion by polymer incompatibility with the gel. Experimental data for the early elution of poly(vinyl acetate) are consistent with an incompatibility mechanism, giving a dependence of the distribution coefficient for polymer-gel interactions on the molecular weight of poly(vinyl acetate).     

凝胶色谱法测定木素磺酸盐电氧化降解产物的相对分子质量分布

 在Waters ALC/GPC244凝胶色谱仪上,使用Waters μ-Ultrahydrogel柱和示差折光检测器,以聚乙二醇作标样,测定了木素磺酸钙的电氧化降解产物的相对分子质量及相对分子质量分布。研究了流动相的电解质种类、离子强度和pH值对标样及试样色谱行为的影响。通过实验确定流动相为0.05 mol/L LiCl溶液,其pH值为6.5。所建立的方法用于木素降解产物相对分子质量分布的测定,具有简便、快速和稳定的特点。     

Gel permeation chromatography of polyethylene: Effect of long-chain branching

The effect of long-chain branching on the size of low-density polyethylene molecules in solution is demonstrated through solution viscosity and molecular weight measurements on fractionated samples. These well-characterized fractions are analyzed by gel permeation chromatography (GPC), and it is shown that the separation of the polymer molecules by this technique is sensitive to the presence of long-chain branching. By using fractions of branched polyethylene possessing differing degrees of branching, one observes that a single curve is adequate in relating elution volume to molecular weight. This calibration curve is applied in the GPC analysis of a variety of commercial low-density polyethylene resins and it is shown, by comparison with independent osmometric and gradient elution chromatographic data, that realistic values for molecular weight and molecular weight distribution are obtained. The replacement of molecular weight M by the parameter [η]M as a function of elution volume, leads to a single relationship for both linear and branched polyethylenes. This indicates that GPC separation takes place according to the hydrodynamic volumes of the polymer molecules. The comparison of data for polyethylene and polystyrene fractions suggests that this volume dependence of the separation will be observed for other polymer–solvent systems.     

淋洗剂凝胶渗透色谱法研究非缔合多组分溶液

A polyglycol solution containing different molecular weight PEG components was chosen as test solution. By comparing the results obtained by conventional gel permeation chromatography GPC(water as eluent, sample solution as injected solution)and Eluent-GPC (PEG sample solution as eluent, the concentrated sample solution ,diluted sample solution, water, and sample solution itself as injected solution respectively), the advantage and potential practical usage of Eluent-GPC were discussed.     

Study on the concentration effects in size exclusion chromatography VII. A quantitative verification for the model theory of concentration and molecular mass dependences of hydrodynamic volumes for polydisperse polymers

A model theory of concentration effects for polydisperse polymers was proposed in 1988. It is successful in relating the concentration of the injected solution to the effective hydrodynamic volumes of peak, the retention volumes of peak and the polydispersity index (Dc = (Vhcw)/(Vhcn) of hydro-dynamic volume distribution for polydisperse polymers at a given concentration. The dependence of the concentration of injected polymer solution on the effective hydrodynamic volumes, the retention volumes of peak and the polydispersity index of hydrodynamic volume distribution for narrow disperse and polydisperse polystyrene, poly(dodecyl methacrylate), poly(tridecyl methacrylate) and poly(methyl methacrylate) in tetrahydrofuran solvent were studied. The proposed theory was verified by these experimental data. Results show that the proposed theory can predict the concentration effects in GPC for polydisperse polymers quantitatively and can provide a theoretical foundation for the two methods of calibrating the universal calibration curves with polydisperse polymers and of determining the second virial coefficients (A2) of polymers. It is found that the determined values of A2 for narrow disperse and polydisperse polymers by the proposed method are in agreement with those obtained by the LALLS method, and the two universal calibration curves with narrow disperse and polydisperse polymers are in excellent agreement.     

Solvation and Adsorption Effects in Gel Permeation Chromatography

Abstract

Saturated hydrocarbons are generally eluted according to molecular volumes in gel permeation chromatography (GPC). Other compounds, containing polar groups such as hydroxyl and carbonyl groups, deviate from the molecular volume/elution count relationship which is prepared using saturated hydrocarbons. The deviation is more or less observed regardless of the kinds of eluents. In this paper, this problem is investigated in detail with respect to infrared(IR) and proton magnetic resonance(NMR) spectra, and concentration dependences of peak heights and elution volumes in GPC. IR and NMR spectra reveal that alcohols, ketones and esters are strongly solvated by eluent molecules such as chloroform and tetrahydrofuran(THF). The solvation effect leads to faster elution for these compounds than expected for aliphatic hydrocarbons. On the other hand, the concentration dependences of elution counts and peak heights prove the adsorption of amines on polystyrene gel in chloroform. In fact, the elution rates of amines and polychlorides are retarded. In the case of aliphatic carboxylic acids, the elution mechanism is more complicated: association and adsorption effects would be overlapped.     

Concentration effects in gel permeation chromatography : IV. Contribution of viscosity phenomena and macromolecular expansion

The changes in elution volumes with the changes in the concentration of an injected polymer solution are caused by several contributing effects. Under model conditions, it is possible to assume only the effect of a viscosity gradient in a zone moving along the column and the effect of the concentration dependence of the hydrodynamic volume of a macromolecular coil. The non-Gaussian shape of the zone and the dependence of the width of the elution curve on concentration are factors that complicate the theoretical treatment of concentration effects. The described physico-chemical model allows to evaluate the ratio of mentioned two contributions in the concentration dependence of elution volumes. According to this model, the contribution of the concentration dependence of the hydrodynamic volume does not exceed about 20% of the total change in elution volume with the varying concentration under real experimental conditions. The efficiency of the columns used and the total injected volume of the polymer solution affect this ratio only negligibly. It is obvious from a comparison with earlier results that these conclusions are not fundamentally changed even by the revised model of the concentration dependence of the swelling factor.     

聚邻氨基苯酚接枝聚己内酯的合成与表征

以邻氨基苯酚为起始原料,合成了一新型接枝聚合物--聚邻氨基苯酚接枝聚己内酯(POAP-gPCL).利用核磁共振仪、红外光谱仪、X射线衍射仪、热重分析仪、电化学测试仪和紫外可见光谱仪等分析手段对聚邻氨基苯酚和聚己内酯接枝的聚邻氨基苯酚进行了结构和性能的表征.结果表明,与聚邻氨基苯酚相比,接枝聚合物表现出较好的热稳定性和电...     

Application of gel permeation chromatography to polyelectrolytes: Salt rejection mechanism and molecular-weight distribution

Gel permeation chromatography (GPC) of polyelectrolytes in dimethylformamide (DMF) is studied. Three methods of monitoring elution (conductimetry, viscosimetry, refractometry) are used to investigate the molecular-weight distribution and, independently, the chemical composition expressed in terms of the ionic charge density as a function of the chain length in two copolymers of acrylonitrile and sodium methallylsulfonate. The distribution on the gel of the neutral salt NaNO₃ added to the DMF and used for elution is discussed in terms of Donnan exclusion; in addition, it is concluded that to obtain the correct molecular-weight distribution, GPC measurements must be performed with an eluent containing a neutral salt at a concentration at least 5 × 10^?2M to prevent electrostatic exclusion. The main difficulty in reaching rigorous conclusions comes from the dependence of the calibration curve on the salt composition of the eluent owing to interactions—dependent on the quality of the solvent—between the polystyrenes used as standards and the porous silica gel. Nevertheless, this perturbation is small and the agreement between the average molecular weights obtained by GPC and by direct determination is good and indicates that the universal calibration proposed for neutral polymers is also valid for polyelectrolytes.     

Synthesis and Some Properties of Graft Copolymers with Uniform Polyoxyethylene Side Chains

Abstract

Graft copolymers with uniform polyoxyethylene (PEO) side chains were synthesized by transesterification of poly(methyl, ferf-butyl fumarate) (PMtBF) or poly(methyl, tert-butyl fumarate-co-styrene) poly-(MtBF-co-St) with potassium alkoxide of PEO monoether. The grafting efficiency increased with enhanced alkoxide reactivity, but the main factor in the ester exchange proved to be the structure of the backbone. This effect was ascribed to the thermodynamic incompatibility between fumaric polymers and PEO. The polymers were characterized by spectral methods, GPC, and DSC. In THF the graft copolymers comprising a polyfumarate backbone with PEO side chains eluted at higher elution volumes than did the backbone homopolymers. In benzene their intrinsic viscosities were lower than those of the backbones. In aqueous eluents, micelles were detected, and their aggregation number depended on the composition of the copolymer and the eluent.     

A simple method for measuring excess adsorption isotherms of organic eluent components on reversed‐phase packing materials

A simple frontal analysis method has been developed for the reliable measurement of excess adsorption isotherms of an organic component on reversed‐phase adsorbents in a series of programmed concentration steps. In the present method, a peak, which is produced by refractive index change in column eluate, is detected at 589 nm; it represents the elution volume of the boundary. The method is applied to the measurement of the excess adsorption isotherms of organic eluent components from water on commercially available reversed‐phase stationary phases. The results are in good agreement with the previously reported isotherms. We also measure the excess adsorption isotherms of organic eluent components from solutions containing electrolytes. There are not any interference peaks on the elution traces. The method is thus reliably applicable to the evaluation of the excess adsorption of organic eluent components in practical systems.     

一组线型聚苯乙烯和星形支化聚苯乙烯的凝胶色谱与热场流分级方法的比较

本文应用热场流分级方法,在两种不同的场强下(△T=30℃、△T=50℃),测试了一系列窄分布聚苯乙烯标样和星形支化聚苯乙烯的淋出体积V_r和分子量M的依赖关系。星形支化物的臂数不同,但臂的分子量相同,上述样品进行了GPC测试,实验表明,由TFFF得到的支化的与线型聚苯乙烯在V_r～M关系上的差别大于GPC的结果,表明链结构对扩散系数的影响大于对分子体积的影响。     

Gel permeation chromatography on polyelectrolytes in aqueous solution

Gel permeation chromatography of water-soluble polymers, with special attention to polyelectrolytes, has been studied. A three-detector system (refractometry, conductimetry, viscometry) is used to characterize the polymers. A single curve is obtained for the calibration of the set of columns taking into account the hydrodynamic volume of the solutes and using a 0.1 N salt solution as the eluent to screen electrostatic forces. The role of the low adsorption of dextran on silica gel is pointed out. The dependence of elution volume on polymer concentration is demonstrated and interpreted in terms of the screening length of the molecules.     

Concentration effects in gel permeation chromatography : V. Differential elution and viscosity phenomena

The viscosity phenomena that take place in the interstitial volume of a chromatographic column and are connected with changes in the concentration and specific viscosity of an injected polymer solution have been studied. These phenomena were also studied under conditions of differential elution when, instead of a pure solvent, solutions of the same polymer at concentrations both higher and lower than those of the injected sample were used as the mobile phase. Linear relationships were found between the elution volume and specific viscosity and between the efficiency and specific viscosity. It was also ascertained that these dependences hold under conditions of differential elution; accordingly, the absolute viscosity of the mobile phase is of minor importance for the phenomena investigated.     

Gel permeation chromatography of poly(styrene-co-divinylbenzene) microgels. Effect of electrolyte concentration in the solvent system dimethylformamide plus lithium bromide

Tightly crosslinked poly(styrene-co-divinylbenzene) microgels with molecular weights in the range 10⁷-10⁸gmol^?1 have been dissolved in dimethylformamide containing LiBr and investigated by gel permeation chromatography and viscometry. The effect of LiBr concentration on the elution volume in GPC can be explained in terms of a diffuse double layer. The product [η]M adequately describes the separation in GPC provided that the LiBr concentration is high and adsorption is absent.     

Application of non-specific fluorescent dyes for monitoring enantio-selective ligand binding to molecularly imprinted polymers

The displacement of non-specific dyes from molecularly imprinted polymer (MIP) chromatographic stationary phases has been used for the detection and quantification of ligand-polymer binding events. A blank polymer and an L-phenylalaninamide-imprinted polymer were prepared using methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as a crosslinker. The MIP is first loaded with dye, and a solution of the dye in the eluent is passed through the MIP. If analyte is injected into the dye solution in the eluent, part of the dye is competitively replaced by the analyte from the MIP. Specifically, the competitive displacement of rhodamine B by amino acids and phenylalaninamide (Phe-NH₂), respectively, has been studied under polar and hydrophobic elution conditions. Enantioselective binding of Phe and Phe-NH₂ to the imprinted polymer was shown to occur in the micromolar concentration range. It is proposed that the displacement of non-specific dyes from MIPs be used for the development of multisensors based upon these highly specific and stable materials, which provide promising alternatives to the use of biological macromolecules in sensor technology. Received: 24 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Application of non-specific fluorescent dyes for monitoring enantio-selective ligand binding to molecularly imprinted polymers

The displacement of non-specific dyes from molecularly imprinted polymer (MIP) chromatographic stationary phases has been used for the detection and quantification of ligand-polymer binding events. A blank polymer and an L-phenylalaninamide-imprinted polymer were prepared using methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as a crosslinker. The MIP is first loaded with dye, and a solution of the dye in the eluent is passed through the MIP. If analyte is injected into the dye solution in the eluent, part of the dye is competitively replaced by the analyte from the MIP. Specifically, the competitive displacement of rhodamine B by amino acids and phenylalaninamide (Phe-NH₂), respectively, has been studied under polar and hydrophobic elution conditions. Enantioselective binding of Phe and Phe-NH₂ to the imprinted polymer was shown to occur in the micromolar concentration range. It is proposed that the displacement of non-specific dyes from MIPs be used for the development of multisensors based upon these highly specific and stable materials, which provide promising alternatives to the use of biological macromolecules in sensor technology. Received: 24 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Liquid chromatography of polymers under limiting conditions of adsorption: III. Role of experimental variables

LC of polymers under limiting conditions of adsorption (LC LCA) is a novel method based on different mobility of (pore excluded) macromolecules compared to (pore permeating) solvent molecules. Polymer sample is injected in a solvent preventing its adsorption within the column. Eluent promotes sample adsorption. Under these conditions, macromolecules cannot leave its initial solvent and elute from the column independently of their molar mass. In contrast, a less interactive simultaneously injected polymer leaves its initial solvent zone and is eluted in the size exclusion mode. As a result, chemically different polymer species can be discriminated. The effect of selected experimental conditions was studied on the LC LCA behavior of poly(methyl methacrylate)s eluted from bare silica gel columns. The parameters were packing pore diameter, injected sample volume and concentration, as well as column temperature. The size independent elution was only little affected by the above parameters and LC LCA produced well-focused peaks. The LC LCA mechanism was operative even at a very large sample of both volume and concentration. This makes LC LCA a robust and user-friendly method, likely suitable also for characterization of minor components of polymer mixtures.