Axial dispersion of polymer molecules in gel permeation chromatography

Gel permeation chromatography is an elution chromatographic process depending on the permeation of the solute through a bed of gel particles. This process is used in the estimation of molecular weight distributions of polymers, since elution occurs in decreasing order of molecular size. The eluting species, however, are not perfectly fractionated, and apparent broadening of the distribution occurs. This broadening results from an axial (longitudinal) mixing of the eluting species. Consideration of the accessible bed volume for each species permits a correction to be made for this axial dispersion. The concept was applied to heterodisperse distributions by solving the resulting simultaneous equations. A least-squares regression may be employed to utilize the experimental data most effectively. The experimental chromatogram can be described in terms of accessible bed volume and dispersion coefficient of each species together with flow rate, sample concentration, and chromatograph column geometry. The chromatogram corrected for the axial dispersion describes the molecular weight distribution more accurately than does the experimentally determined curve. The correction procedure was applied to a well-characterized polystyrene; the results of the gel permeation chromatography show excellent confirmation of the results of fractionation and of other instrumental analyses.     

On the separation mechanism of gel permeation chromatography

The separation mechanism of gel permeation chromatography was investigated by static experiments. It was found that the solute molecule is excluded from part of the inner space of the gel particle, which is entirely available to the solvent molecule. The excluded volume, ΔV, increases with increase of molecular size of the solute. A linear relationship was observed between the ΔV and the logarithm of molecular size. Excluded volume was found to be independent of solute concentration as was expected. Absorption effect was negligible with polystyrene gel. However, a strong effect was observed between acids and polydextran gel. The possibility of using absorption effects to increase the separability of GPC is suggested.     

Production and properties of polyacenaphthylene—VI. Influence of polymerization conditions on chain structure

Low molecular weight polyacenaphthylenes produced by azo initiators through thermal or free-radical means are slightly yellow. The colouring is more intense the higher the polymerization temperature. It can be shown through spectroscopic investigations that the colouring is caused by conjugated double bonds in the polymer backbone chain and/or by the location of double bonds next to the ester end-groups. Chain branching influences the chain form and the hydrodynamic volume of the molecule; it can be used to explain the behaviour of the polymers in gel permeation chromatography.     

Towards Unveiling the Exact Molecular Structure of Amorphous Red Phosphorus by Single‐Molecule Studies

Since the discovery of amorphous red phosphorus (a‐red P) in 1847, many possible structures have been proposed. However, the exact molecular structure has not yet been determined because of its amorphous nature. Herein several methods are used to investigate basic properties of a‐red P. Data from scanning tunneling microscopy (STM) and gel permeation chromatography (GPC) confirm that a‐red P is a linear inorganic polymer with a broad molecular weight distribution. The theoretical single‐molecule elasticities of the possible a‐red P structures are obtained by quantum mechanical (QM) calculations. The experimental single‐molecule elasticity of a‐red P measured by single‐molecule AFM matches with the theoretical result of the zig‐zag ladder structure, indicating that a‐red P may adopt this structure. Although this conclusion needs further validation, this fundamental study represents progress towards solving the structure of a‐red P. It is expected that the strategy utilized in this work can be applied to study other inorganic polymers.     

Branching in bisphenol a polycarbonate: Gel permeation chromatography,viscometry and light scattering

Branching in bisphenol A polycarbonate has been investigated by fractionation, gel permeation chromatography, viscometry and light scattering. The samples studied (Makrolon 3000 and 3000L) are branched, Makrolon 3000 more so than Makrolon 3000L. The variation of the branching parameters with molecular weight is suggestive of random branching. Comparison of the molecular weight distribution with that expected for random trifunctional branching suggests an average of about half a branch point per weight-average molecule in Makrolon 3000.     

On-Stream HPLC Determination of Residual Ethylene Oxide and Propylene Oxide in Glycerol Based Polyol Synthesis

Abstract

A simple automated HPLC scheme was developed to monitor synthetic polymerization reaction on-stream. Chromatographic conditions that affect the separation of the reaction species from the reaction product and base catalyst using high-performance aqueous gel permeation chromatography were also studied. Reactor samples are automatically drawn from the reaction vessel through a micro-loop sampling valve/actuator assembly and transferred to the chromatographic system via stainless steel tubing without interruption of the mobile phase flow. The resulting chromatograms, monitored by a refractive index detector, of reactants and products are continuously measured at intervals during the reaction automatically and unattended. Application of this system for the reaction of propylene oxide and ethylene oxide to high molecular weight polyols is presented.     

Rapid analysis of membrane glycopeptides by gel permeation high-performance liquid chromatography

A rapid procedure for the analysis of glycopeptides has been developed using gel permeation high-performance liquid chromatography (HPLC). Glycopeptides derived by exhaustive pronase digestion of glycoproteins from radiolabeled human tumor and normal cell lines were chromatographed on DuPont GF-250 and GF-450 gel permeation columns in buffers containing non-ionic detergents. Effective separations of glycopeptides ranging in molecular mass from less than 600 daltons to more than 20,000 daltons, equivalent to the separation range of Sephadex G50 chromatography, were achieved in 7 min. The separations were dependent upon the use of an isocratic mobile phase, that contained a low-ionic-strength Tris buffer and Nonidet P-40 or Triton X-100. The mobilities of protein standards indicated the occurrence of a biphasic elution system, which favored the separation of species with molecular masses below 20,000 daltons. Glycopeptides isolated by this method could be applied directly to lectin or ion-exchange columns or could be digested with neuraminidase, endo H or other enzymes without further treatment. Removal of sialic acid from the glycopeptides caused a dramatic increase in retention time. Using this method, glycopeptides could be isolated rapidly and in high yield. The ease, speed and reproducibility of the separations and compatibility of the solvent systems with affinity or ion-exchange chromatography techniques make this gel permeation HPLC method an ideal initial step in the purification of glycopeptides.     

Unraveling the Bimodality of Polypropylene Film Grades Using Rheological Shear and Elongational Measurements: Inconsistent Results of Gel Permeation Chromatography

As the main parameter to describe the molecular structure of a linear polymer, molecular weight distribution of five different polypropylene grades was evaluated through measurements of gel permeation chromatography and rheology experiments. From their dynamic shear data, the relaxation spectra, h(τ), were calculated from which molecular weight distribution was estimated using molecular viscoelastic theories and then compared with the gel permeation chromatography results. Generally good agreement, yet with narrower molecular weight distribution rheology curves was found. Exception was observed for one grade for which rheological data predicted bimodal distribution curve comprising a small shoulder of high molecular weight, not seen in the corresponding gel permeation chromatography curve. Additionally, a higher value of the generalized mixing parameter (i.e. β) was found for this bimodal grade which was attributed to an increase in the number of entanglements per chain and better network connectivity. Furthermore, measurements of the transient extensional viscosity also revealed enhanced strain hardening and melt strength for this particular grade. The results showed that small amount of high molecular weight fraction of linear chains could drastically alter the processing behavior of polypropylene film grades.     

Hydrodynamic Fractionation of Macromolecules. I. A Simple Theory

A new mechanism for separation in gel permeation chromatography (CPC) or gel filtration has been developed based upon the postulate that flow occurs through the gel phase. On the basis of the hydrodynamic nature of the separation mechanism, the new name Hydrodynamic Fractionation is proposed. A theory has been formulated for the case of equal pore size in the gel phase and equal sized spaces between the beads. This theory predicts the elution volume vs molecular weight curve. The flow-rate dependence of the separation peaks is investigated.

The theoretically predicted relationship between molecular weight and elution volume compares very well with the gel permeation experiments using glass beads as packing probably because these packings correspond most closely to the assumptions in the theory. In the cross-linked polymer packing where a large distribution of pore sizes exists the theory does not fit well; however, it does predict the general shape of the curve. The flow-rate dependence of the separation peaks is experimentally the same as qualitatively predicted. Also the experimental findings of equilibrium experiments were correlated with the corresponding GPC data using the present theory.     

Isolation and purification of uremic middle molecules by multi-step liquid chromatography

Isolation and comparison of uremic sera and urine and normal sera and urine were performed by gel permeation chromatography, anion exchange chromatography and re-versed-phase high performance liquid chromatography. Two uremic middle molecular fractions (A and B) were obtained from uremic sera and urine and normal urine by gel permeation chromatography, but not from normal sera. The anion exchange chromatographic results of fraction A from different origins demonstrate that subfraction A-3 could be excreted in urine by healthy subject, but accumulated in uremic serum for renal failure of patient with uremia. After desalinization subfraction A-3 was analyzed by MALDI-TOF-MS. The results show that subfraction A-3 consists of six compounds with molecular weight 839, 873, 1007.94, 1106, 1680 and 2015 respectively. Finally, by reversed-phase high performance liquid chromatography, subfraction A-3 was further resolved into six independent fractions. Thus, the isolation and purification of six middle molecular c     

Laser light scattering as GPC detector

The use of low angle laser light scattering (LALLS) as a detector in gel permeation chromatography (GPC) is discussed. The advantage of this technique is primarily based on the ability of LALLS to continously measure the absolute molecular weight and also to detect minute concentrations of high molecular weight species such as microgel. The weakness of the system is in the low sensitivity for low molecular weight material. In this paper, our experience of the KMX-6 from Chromatix illustrates the possibilities for the characterization of polymers by the combination of LALLS and GPC. The applications discussed are mainly from our work with polyethylene and poly(vinyl chloride). Special emphasis is given to the determination of long chain branching and microgel.     

Relationship between physicochemical characteristics and functional properties of chitosan

In order to select an ideal chitosan (CS) species as a material for implantation vehicle to control drug release in the body, the relationship between physicochemical characteristics (including molecular weight, degree of deacetylation, and viscosity) and functional properties (including ability to form spherical gel, control of drug release from CS gel, and biodegradation of CS) was investigated for various CS. The ease of spherical gel formation in aqueous amino acid solution or aqueous solution containing metal ions was affected mainly by viscosity of the CS solution. Drug diffusion rate from the CS gel was controlled by density of the gel matrix structure, which was governed by viscosity of the CS solution prior to gelation. Biodegradation of CS tended to vary with degree of deacetylation. However, linear relationships for these trends were not observed, and the possibility that characteristics other than CS molecular weight, degree of deacetylation, and viscosity of the CS solution, such as distribution of acetamide groups in the CS molecule affect functional properties of CS, was also indicated. These observations demonstrate that CS functions are affected by various CS characteristics and that investigation of individual CS characteristics is important for the selection of the appropriate CS as a material for drug delivery vehicles.     

Measurement of molecular mass of chitosan oligomers

The molecular mass of chitosan oligomers in the range of (2-5) × 10³ was measured using viscometry and gel permeation chromatography. The use of viscometers with a flow time of at least 108 s (0.33 M CH₃COOH + 0.3 M NaCl as a solvent, 21°C, [η] = 3.41M ^1.02) makes it possible to determine the molecular mass of chitosan oligomers up to 1.98 × 10³. In this case, the maximum divergence in the molecular mass values of oligomers determined by viscometry and gel permeation chromatography does not exceed 4%.     

Evaluation of field desorption mass spectrometry for the analysis of polyethylene

Field desorption mass spectrometry (FD-MS) has been evaluated for the analysis of low molecular weight polyethylene by using samples in the molecular weight range 600–2000 u as determined by gel permeation chromatography. The repeat units and end groups were characterized by FD-MS, but it was demonstrated that accurate molecular weight distribution data cannot be obtained for polyethylene by FD-MS because there is mass discrimination against the higher molecular weight polymers.     

凝胶色谱法测定聚丙烯腈相对分子质量的验证

采用窄分布的聚苯乙烯和聚甲基丙烯酸甲酯分别对凝胶色谱柱进行标定,测定了聚丙烯腈的相对分子质量。聚苯乙烯、聚甲基丙烯酸甲酯标定法得到聚丙烯腈的重均相对分子质量分别为5.008×10^5,2.929×10^5,两种标定方法所得数据相差较大。采用光散射法验证窄分布标准样品标定测试数据的准确度,得到聚丙烯腈的重均相对分子质量为1.485×10^5,与窄分布聚合物标定凝胶色谱法得到的数据相差很大,表明凝胶色谱标定法测定聚丙烯腈的相对分子质量是一种相对方法,其量值无法实现准确溯源。     

Preparation of tea glycoprotein and its application as a calibration standard for the quantification and molecular weight determination of tea glycoprotein in different tea samples by high-performance gel-permeation chromatography

Tea glycoprotein (TGC) was purified by Sephadex G-100 gel filtration, and its purity and molecular weight (MW) were determined by high performance gel permeation chromatography. The gel permeation chromatography (GPC) elution behavior of TGC on an Ultrahydrogel 500 (7.8×300 mm) column was studied using a mobile phase with various concentrations of NaCl. A dextran T system was found to be unsuitable as MW calibration standards in GPC because the MW of TGC was changed with the change of ionic concentration in the mobile phase. Thus, the purified TGC obtained in this study was standardized and used instead as the calibration standards for the determination and comparison of TGCs in tea samples collected from different geographic locations and species varieties. The GPC was run at 35°C on an Ultrahydrogel 500 column (7.8×300 mm) with a refractive index detector. Distilled water was used as the mobile phase at a flow rate of 0.6 ml·min⁻¹. The calibration curve was linear over the TGC concentration range of 0.604–6.04 mg·ml⁻¹, with a correlation coefficient of r=0.9997. The TGC mass recovery ranged from 80.4 to 93.2%, with a relative standard deviation of 5.42%. The assay method developed in this paper was found to be simple, reproducible, and reliable and, thus, ideally suitable for the quality control of TGC-derived products and raw materials.     

Coarsening of alkane-in-water emulsions stabilized by nonionic poly(oxyethylene) surfactants: the role of molecular permeation and coalescence

We produce different alkane-in-water concentrated emulsions stabilized by the same nonionic surfactant, and we follow their kinetic evolution by granulometry. The size distribution becomes remarkably narrow during the first stages of coarsening and progressively turns to a wide function as time passes. We get evidence that the size evolution occurs under the effect of molecular permeation and coalescence. A second hydrophobic species of large molecular size is dissolved in the dispersed phase. This latter is expected to inhibit the permeation mechanism, and coalescence should act alone. Surprisingly, coalescence is also suppressed, even at a very low concentration of the second component (approximately 1% w/w). We vary the chemical nature and concentration of the second species, and we propose a simple mechanism to explain the stabilizing effect with respect to coalescence.     

Gel permeation chromatography of branched polyethylene

The effect of long-chain branching must be considered in gel permeation chromatography to evaluate the molecular weight polydispersity of branched polyethylenes. Osmotic molecular weights of fractions of branched polyethylene were correlated with elution volumes; weight-average and number-average molecular weights of a branched polyethylene were determined. Molecular weight changes on crosslinking polyethylene by ionizing radiation are accompanied by branching and cannot be simply interpreted by gel permeation chromatography.     

Electron beam crosslinking of poly(vinylmethyl ether)

The electron beam induced branching of poly(vinylmethyl ether) (PVME) in bulk and in isopropanol solutions has been studied by gel permeation chromatography. The branching probability of bulk PVME induced by high-energy electrons can be characterized by gel permeation chromatography and a simple probability constant obtained. In isopropanol solutions this branching probability is not constant as a function of dose and is found to decrease with decreasing concentration. These results indicate the importance of solvent effects on the crosslinking of PVME in isopropanol solution by electron beam radiation. © 1994 John Wiley & Sons, Inc.