Preparative gel permeation chromatography. I. Polypropylene

Preparative gel permeation chromatography was used to produce a number of polypropylene reference samples, within the molecular weight range of 10,000–600,000, from commercial materials. Some of these materials were degraded in a controlled manner to give base materials having suitable molecular weight characteristics. A procedure has been developed using a single preparative column packed with equal quantities of Styragel with nominal exclusion limits of 10², 10³, 10⁴, and 10⁵ nm. The volume of solvent for recovery was minimized by use of higher loading factors than in analytical GPC (some 2–20 times more polymer was thus fractionated in each experiment). Under these conditions the fractions first eluted were sharpest having polydispersities of about 1.5. First fractions, from different base materials, were characterized by analytical GPC, and those of similar molecular weight and polydispersity were combined to give the reference samples. Refractionation was necessary with the highest molecular weight base material because the first stage fractions were not sharp enough. Some of these fractions were recovered at elution volumes where much lower molecular weight material was expected. Comparison with results from the other base materials indicates that the primary cause of the spreading is not overloading. This spreading is explained in terms of slower partitioning of the larger molecules between the interstitial fluid and the gel particles.     

A study of micelles in a base lubricating oil by gel permeation chromatography

Micellar solutions of two polystyrene-poly(ethylene/propylene) block copolymers in a base HVI lubricating oil were studied by gel permeation chromatography (g.p.c.). The Styragel columns employed in the work were calibrated using polyisobutylene fractions. At 50°C each copolymer solution gave a single sharp peak which was well within the resolution of the columns, indicating that the micelles were able to enter the pores of the Styragel and elute through the columns as stable particles. Analysis of the chromatograms showed that the micelles had narrow size distributions. Light scattering provided a method of determining the weight-average molecular weights and apparent mean-square radii of gyration of the micelles. Molecular weights determined from g.p.c. using the universal calibration procedure were in fair agreement with the light scattering values. Unfortunately g.p.c. experiments attempted over the range 75°–150°C were unsuccessful because the Styragel strongly absorbed the copolymer at these higher temperatures.     

Exclusion chromatography using controlled-porosity glass. I. Comparison with styrene gels

The instrumental parameters influencing the calibration of a gel permeation chromatograph (GPC) using column packings of Corning CPG-10 porous glass have been evaluated. The porous glass system used a set of columns 1.6 × greated in length and 0.6 × smaller in diameter than the Styragel system, which was used for comparison. The dependence of retention volume of polystyrene calibrants on eluent flow rate and on sample size was similar in both systems. Samples of poly(methyl methacrylate), poly(vinyl choloride), and poly(4,4′-isopropylidenediphenylene 1,1,3-trimethyl-3-phenylindan-4′,5-dicarboxylate) fractions were examined, and the molecular weights, obtained by using the hydrodynamic volume concept, were in satisfactory agreement with the light-scattering data for both chromatographic systems. Corrections for axial dispersion, for the polyester fractions and polystyrene samples, were probably equivalent in these two chromatographic systems.     

The use of porous glass as a column packing for gel permeation chromatography

Use of porous glass with a broad pore-size distribution as a column packing for gel permeation chromatography has been investigated. The porous glass is readily available, and columns are packed easily and have excellent mechanical stability. Separations of polystyrene over molecular weight ranges of 500–2,000,000 have been obtained. Porous glass thus appears to be a useful packing material for gel permeation chromatography.     

Gel permeation chromatography: Fast flow rate studies with porous glass column packings

Comparisons have been made between gel permeation chromatograms obtained at solvent flow rates of 1.0 and 4.5 ml/min. Using a 24 ft column series packed with Bio Glas the pressure drop was 200 lb/in² which is within the operating range of all gel permeation chromatographs and is considerably less than when crosslinked polystyrene gels are used. The chromatograms from the Bio Glas packed columns exhibited skewing, similar to that reported previously for polystyrene gel packed columns. An analysis of these chromatograms indicated that the increased peak width caused by the faster flow rate was serious. Typically M _w/M _n values calculated at 4.5 ml/min were double their true values. Additionally skewing badly distorted the differential molecular weight distribution for molecular weights of 411 000 and higher. Previous studies in this area had not described quantitatively this adverse effect of increasing solvent flow rate in gel permeation chromatography.     

Extraparticle diffusional effects in gel permeation chromatography. II. Experimental results

Experiments coupled with a systems analysis were conducted on chromatogram dispersion, or zone broadening, in gel permeation chromatography (GPC). Three components of a Waters Associates Model 200 chromatograph, each of which is a potential cause of dispersion, were considered; these are: the packed column, with extraparticle dispersion only; the empty tubing, between pump and columns, columns and detector, etc.; and the detection system, viz., the differential refractometer cell. Toluene solvent was used and the solutes whose dispersion was studied included orthodichlorobenzene (ODCB) and narrow-molecular-weight polystyrene standards having molecular weights of 900, 20,400, 51,000, 97,200, and 160,000. Nonporous glass beads, 50 μ in diameter, were used as column packing. Two diameters, 1 mm and 0.5 mm, of stainless steel tubing were studied. In addition to the usual rectangular pulse sample injection, a step input mode for solute introduction was also used. The empty tubing was found to contribute significantly to the degree of dispersion and to skewness of elution curves. Anomalous bimodal characteristics of the elution curves were also observed which could only be ascribed to the empty tubing. These phenomena depended markedly on parameters such as tube diameter and length, and solute concentration and molecular weight. Dispersion in the packed column, although important, was found to be symmetrical (Gaussian) and less sensitive to these parameters than in the empty tubing, especially with respect to molecular weight. Dispersion in the cell was believed to be insignificant relative to the packed column and empty tubing.     

Polystyrene gel permeation chromatography packings grafted with polar monomers—synthesis and use in aqueous organic mobile phases

A number of polystyrene resins of chromatographic quality (5–10 μm) have been prepared with significant residual double bond contents (～ 2 mmol·g^?1). These groups have been used as sites for the grafting of eight polar macromolecules in an attempt to produce a thin uniform coating of the resin surface. Three different grafting procedures have been examined and all products characterized in terms of their toluene and water imbibition. Materials showing promise as universal column packings for gel permeation chromatography have been synthesized on a larger scale and packed in tetrahydrofuran (THF) into standard columns. The plate count of each packed column has been evaluated, and the chromatographic performance of each assessed using polystyrene standards when the eluent was THF and polyethylene oxides when water and methanol were employed. The results are discussed in terms of some simple models describing the grafted resins.     

The optimum taper angle for ethanol fermentation in a packed-bed column reactor

In ethanol fermentation, tapered columns facilitate the liberation of CO₂ and, since the bed expands through a larger cross-sectional area, smaller pressure drops occur. In this work, 0°, 2°, and 4° tapered columns, containing Saccharomyces cerevisiae entrapped in beads of K-carrageenan, were operated for continuous production of ethanol from glucose. The column inlet diameters and the bead volume were maintained constant for the three columns. With decreasing taper angle, increasing feed glucose concentration, increasing feed flow rate and increasing bead volume in the reactor, the pressure drop across the bed increased. There was no significant difference between the ethanol productivities obtained in the 0°, 2°, and 4° tapered columns when a packed volume of 52% of the total volume was examined. Increasing the packed volume to 84% of the total caused the cylindrical column to become inoperable due to pressure buildup and bead compression. When the columns were packed to 84% capacity, the productivity and pressure drop values obtained on the 2° and 4° tapered columns did not significantly differ. For a feed concentration of 150 g glucose dm^?3 and a residence time range of 5.4–15.94 h, the pressure drop varied between 4.5 × 10³ and 1.28 × 10⁴ Pa in the 2° and between 4 × 10³ and 7.98 × 10³ Pa in the 4° tapered column. Conversion in the 2° tapered column varied from 94% to 78.8% and in the 4° tapered column from 92.6% to 78.8%. Defining optimum taper angle as the smallest angle which allows for stable operation without any pressure buildup, the taper angle of 2° was selected as nearest to the optimum value.     

Gel permeation chromatography: Physical characterization and chromatographic properties of corning porous glasses

Five porous glasses, manufactured by Corning, reputed to have very narrow pore size distributions, have been characterized by mercury porosimetry, nitrogen adsorption–desorption isotherms, and electron microscopy. The characteristics of these glasses as packing materials in gel permeation chromatography have been determined. Using polystyrene solutes and toluene solvent at room temperature, the glasses in series combination of columns are capable of separating molecular weights from a few thousand to several million. These glasses are compared with other available materials for column packings in gel permeation chromatography.     

Fast Gel Permeation Chroma tog raphy

Abstract

A systematic study of the major factors influencing fast analysis by gel permeation chromatography is presented. The study included the effects of (a) solvent flow rate [1–35 ml/min], (b) sample concentration [0.05–0.5%], (c) sample molecular weight [41–411,000 mol wt] and (d) particle size of column packing [10–42μ]. The effect of the operating temperature at the high flow rates was also investigated.     

Fractionation of dextran using repetitive batch chromatography

The fractionation of broad dextran fractions using preparative scale gel permeation chromatography has been carried out. A batch system was used, consisting of ten borosilicate columns, each of 5.1 cm i.d. and 70 cm long and packed with Spherosil XOB075 porous silica beads. The repetitive injection technique was employed and the effects of feed, charge volume and concentration on the molecular weight distribution of the products were evaluated.     

Change in GPC elution volume of polymers by adsorption onto porous glass as column packing

The elution volume of polystyrene or of poly(ethylene glycol) of various molecular weights was measured in both tetrahydrofuran and benzene at 40 or 60°C by means of gel permeation chromatography utilizing columns packed with crosslinked polystyrene gel or porous glass. When the polystyrene gel was used as the column packing, a relationship between log [η]M and the peak elution volume for polystyrene agreed with that for poly(ethylene glycol). Using columns packed with glass, however, the elution volume of polystyrene was smaller than that of poly(ethylene glycol) at the same log [η]M. The results are considered to be attributable to the adsorption of poly(ethylene glycol) onto the glass. The effect of the adsorption on the elution volume was evaluated by assuming a universal calibration for columns containing porous glass; the deviation of the elution volume from the universal calibration curve increased with increase in molecular weight. At lower temperatures, even polystyrene was adsorbed onto the glass. Therefore, to reduce the adsorption of polymers on glass, it is necessary to increase the temperature or use surface treatment when porous glass is used as a GPC column packing.     

Reference samples of poly(vinylalcohol) for molar mass measurement in aqueous solution

The preparation and characterization are described of reference samples of poly(vinylalcohol) spanning the range of molar mass 20–350 kg mol^?1. Evidence is presented that long-chain branching has no significant effect on the relation to gel permeation chromatography of the molar masses of the poly(vinylalcohol) samples and those of the corresponding poly(vinylacetate) samples. The measured molar masses are shown to be consistent with the elution behaviour in aqueous gel permeation chromatography with two column materials.     

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.     

High Resolution Gel Permeation Chromatography-Using Recycle

Abstract

High resolution in gel permeation chromatography has been accomplished by use of long columns, since commercial rigid gels afford relatively fixed capacity ratios and since plate numbers of equivalent columns are additive. To overcome the high cost and high pressure requirement of long columns often required to resolve discrete species, high resolution gel permeation chromatography may be attained in commercial GPC equipment by recycle operation through the reciprocating pump, GPC column, and detector. However, peak width increases with the number of cycles (μ). Since the contained volume of the closed recycle system is constant, as v increases the peak width (W) of the distribution will eventually exceed the volume of the system and peak overlap will occur. This presentation considers the increase in W and provides a method of “flush and draw off” to prevent sample overlap. Analytical and preparative scale separations were investigated, using both small and macromolecules. The effects of sample load and flow rate on-resolution with recycle operation were investigated.     

Gel permeation chromatography calibration based on fractal geometry

The previously developed model [Polym Bull 2000, 44, 525] used to characterize the porous gel inside a gel permeation chromatography (GPC) column, has been extended to also include the interstitial space between the macroscopic gel particles. The hydrodynamic dimensions for 12 polystyrene (PS) standards, measured by GPC with differential refractive index (DRI), differential viscometry (VISCO), and multiangle laser light scattering (MALLS) detectors, have been used to determine the fractal parameters of the polystyrene–divinylbenzene gel corresponding to four commercial columns. The new developed model enables to predict the calibration curve for the sets of coupled columns based on the parameters of each column. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 771–777, 2004     

Dextran fractionation using preparative scale continuous chromatography

The continuous fractionation of dextran feedstocks using preparative scale gel permeation chromatography is reported. A semi-continuous counter-current chromatographic refiner has been used, which consisted of ten 5.1 cm i.d. × 70 cm long stainless steel columns, packed with Spherosil XOB075 porous silica beads. The system has proved successful in removing the very low and the very high molecular weight fractions and obtaining products of the required specification. Over 90% recoveries have been achieved at throughputs of 0.470 kg dextran h^?1.     

Extraparticle diffusional effects in gel permeation chromatography. I. Theory

A systems approach is applied to the analysis of chromatogram resolution dispersion, or zone broadening, in gel permeation chromatography (GPC). Three possible sources of dispersion are considered; these are: the packed columns; the empty tubing between pump and columns, columns and detector, etc.; and the detection system, viz., the differential refractometer cell. It is shown that empty tubing can contribute significantly to the degree of dispersion and to skewness of elution curves and that this dispersion should depend on molecular weight of solute (polymer) and diameter and length of the tubing. The importance of dispersion in the empty tubing is compared with that in the packed columns and refractometer cell.     

Separation of coal-derived liquids by gel permeation chromatography

Coal-derived liquids, obtained from pilot plants and bench-scale reactors, have been separated by gel permeation chromatography into aromatic, phenolic, and asphaltenic fractions, where asphaltenes and long-chain hydrocarbons are in the same fraction. The Chromatographie system uses 10 nm μStyragel columns and solvents such as tetrahydrofuran (THF) and toluene. The separation is reasonably clean and almost devoid of overlapping. The saturated hydrocarbons are separated from the asphaltenes by vacuum distillation. Aromatic, phenolic and aliphatic fractions are characterized by high-resolution gas chromatography—mass spectrometry. The phenolic fraction contains alkylated phenols, indanols, and naphthols. The aromatic fraction is composed of alkylated benzenes, indans, naphthalenes and small amounts of multi-ring aromatics such as alkylated fluorenes and pyrenes. Most of the long-chain hydrocarbon fraction is of straight-chain alkanes ranging from tetradecane to tetratetracontane. Some branched alkanes, such as pristane and phytane, are also present. If olefins are present in the sample they also separate with the long-chain hydrocarbon fraction. Although various analytical data such as i.r., n.m.r., molecular size distribution and elemental composition of asphaltenes have been obtained, the chemical characterization is not complete. The gel permeation Chromatographie separation technique, as discussed in this paper, is very useful for fast analysis of any coal-derived liquid.     

High performance g.p.c. with crosslinked polystyrene gels: influence of particle size distribution

Spherical crosslinked polystyrene gel particles have been separated by air classification into fractions having average particle diameters in the range 10–40 μm. The particle size distributions have been shown to be narrow by Coulter Counter measurements. G.p.c. column performance improves as the average particle diameter decreases and columns packed with gel fractions having a number-average particle diameter below 20 μm give plate counts in excess of 3000 plates per foot. Plate height results as a function of eluent flow rate suggest that chromatogram broadening due to mobile phase dispersion is reduced in columns packed with spherical particles having a narrow size distribution.