Treating the polyelectrolytes as polymers with a draining effect. II. The behavior in the gel permeation chromatography

The behavior of the polyelectrolytes in the gel permeation chromatography (GPC) can be better understood if the modified universal calibration (log([η]M/Φ) vs. elution volume) is used instead of the “classical” universal calibration (log[η]M vs. elution volume). The value of Flory's parameter Φ is obtained from an equation established for nonionic polymers presenting a draining effect, considering that polyelectrolytes also behave as polymers with a draining effect. The modified universal calibration does not apply as successfully to polyelectrolytes as to nonionic polymers, because of their electrostatic exclusion in the pore surface of the GPC columns. Nevertheless, when polyelectrolytes are found in a high salt concentration solution, the modified universal calibration can be used to obtain their molecular mass, using nonionic hydrosoluble polymers as standard polymers. Moreover, considering polyelectrolytes as polymers presenting a draining effect and applying the modified universal calibration provides a better explanation for the electrostatic exclusion of these polymers from the pores of the GPC columns, using the Dubin–Tecklenburg model. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1106–1113, 2006     

Gel Permeation Chromatography of Polyelectrolytes

Abstract

The mechanisms are discussed which control the GPC elution of ionic solutes, both the polyelectrolytes and the low molecular salts. The processes involved are quite general and valid in organic and in aqueous solvents. The conclusion is that gel permeation chromatography is a powerfull method to characterize poly-electrolytes; and it is shown that the correct data on molecular weight distribution can be obtained when the ionic content in the eluent is larger than 5.10^?2 M and when the concentration injected is lower than the critical overlapping concentration. The interpretation of chromatograms can be performed using the universal calibration and a viscosimetric detector.     

Aqueous GPC of electrolytes and polyelectrolytes

The gel permeation chromatography (GPC) of polyelectrolytes is discussed. The electrostatic exclusion is demonstrated using simple electrolytes with different eluents. The data for aqueous free salt solutions of polyelectrolytes are interpreted. The osmotic coefficient is deduced and its dependence on molecular weight and polymer concentration reported. In salt eluents, the Donnan exclusion is discussed. The universal calibration obtained with different standards in aqueous solution is shown to be valid and identical to that obtained in an organic solvent using polystyrene standards.     

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.     

Substrate–polymer interactions in liquid exclusion chromatography (GPC) in N,N-dimethylformamide

The importance of nonexclusion effects in the GPC behavior of several stationary phases was investigated with DMF, 0.01M LiBr, as the mobile phase. Various low MW solutes and narrow MWD polymers, encompassing a wide range of polarities, were studied. The elution of the polymers was examined in terms of “universal calibration” behavior. Styragel and silanized glass both exhibit affinity for apolar polymers in DMF; for the former substrate this effect shows a strong inverse dependence on MW. As a consequence, application of polystyrene calibration curves to GPC analysis of more polar polymers with these substrates leads to overestimations of MW parameters. These errors are not corrected when universal calibration procedures are used. Ideal exclusion chromatography is exhibited by a number of polymers on untreated porous glass substrates. However, polymers with strong hydrogen-bonding functionality appear to be susceptible to marked adsorption in this system.     

Aqueous gel permeation chromatography of polyelectrolytes and salt exclusion effect

The dependence of the elution volume of NaCl samples is discussed as a function of the volume and concentration injected and of the ionic strength of the eluent. The same is done with two fractions of polystyrene sulphonic acid in the sodium form. It is concluded that the exclusion depends directly on the screening parameter proportional to $\text{μ}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ for NaCl and that a steric parameter has to be added with polyelectrolytes, depending on the molecular weight and on the ionic strength of the eluent. The behaviour is directly correlated to the pore size distribution in the gel.     

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).     

High performance microcolumn exclusion chromatography of proteins and peptides

A new method for the determination of the molecular weight of proteins and peptides has been developed. It is based on microcolumn exclusion chromatography in trifluoroacetic acid on silica gel sorbents of different porosities with a linear molecular-weight calibration dependence in the range of 5 × 10² - 7 × 10⁴ Da. It was shown that in this eluent proteins and peptides adopt the random-coil conformation and do not undergo hydrolysis for 2–3 days at room temperature.     

Peculiarities of polyacrylamide analysis by aqueous GPC

Various commercially available stationary phases of gel permeation chromatography (GPC) were tested to determine their effectiveness in aqueous exclusion chromatography. It was found that controlled pore glass (GPG) is the most suitable material for the separation of polyacrylamides and poly(acry1amide-co-sodium acrylate), dextrans, and poly(sodium styrene–sulfonates) in 0.1M aqueous Na₂S0₄ solutions of ionic strength 0.3. A calibration curve was established by using broad molecular weight distribution polyacrylamide standards in a trial and error procedure. To avoid artificial oscillations on the evaluated distribution curves a cubic B-spline representation of the calibration curve was used instead of the conventional polynomials. By applying this system the solution instability of polyacrylamides was observed by GPC and is discussed because of its general importance to the applicability of indirect molecular weight determination methods for polyacrylamides. The effectiveness of aqueous GPC was demonstrated in an evaluation of thermal degradation measurements of polyacrylamides. Finally, the feasibility of universal calibration of aqueous GPC by means of poly(sodium styrene–sulfonates) was investigated. It is apparent that in spite of some problems concerning adsorption of the polymer universal calibration is a successful tool for calibrating aqueous GPC.     

Analysis of chitosan by gel permeation chromatography

The effect of γ-radiation on the average molecular weight and the molecular-weight distribution of chitosan has been studied. The analysis of samples by gel permeation chromatography/size exclusion chromatography (GPC/SEC) has shown that the amount of high-molecular-weight fractions decreases and the amount of fractions containing low-molecular-weight chitosans (<50 kDa) increases with an increase in the radiation dose. The radiation-chemical yield of degradation is 11.0 particle/100 eV.     

Method of calibrating gel permeation chromatography with whole polymers

Column systems for gel permeation chromatography are usually calibrated by eluting a series of sharp polymer fractions of known molecular weights and by correlating their elution volumes with molecular size or weight. A different method for calibration is proposed in which only one polymer sample, with a broad, well-characterized molecular weight distribution, is used. The cumulative distribution and the integrated, normalized GPC chromatogram are successively superimposed, and molecular weights and corresponding elution volumes are correlated. It is found that calibration curves obtained in this manner show a definite curvature. A possible explanation and correction for this behavior is given, based on the concentration dependence of elution volumes.     

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.     

Steric exclusion and lateral diffusion in gel-permeation chromatography

The peak separation in gel-permeation chromatography (GPC) is attributed to the contributions of the steric exclusion and the lateral diffusion processes. The advantage of using the distribution coefficient K_GPC of the solute molecule in interpreting the GPC separation mechanism is assessed. The physical significance of K_GPC and its relation to measurable GPC parameters are examined in detail. A simple mixing experiment for determining the exclusion effect is described. The results of this experiment, as well as those of the flow rate study, show that the exclusion effect plays the primary role in GPC peak separation. For a column packed with Bio-Rad porous glass of 200 Å designation, the diffusion effect does not contribute significantly to peak separation. However, for the case of a Waters Associates column packed with polystyrene gel of 10⁴ Å designation, both the exclusion and the diffusion effects are shown to be important. A diffusion theory which includes the concept of a restricted diffusion coefficient is proposed to interpret the diffusion effect observed in the polystyrene gel column. The results of the theoretical calculation are found to agree with the observed flow rate dependence of the calibration curve.     

The determination of the molecular weight distribution of amylose by gel permeation chromatography

The universal calibration for gel permeation chromatography (GPC) has been applied to amylose and dextrans. The molecular weight distribution of amylose has been measured starting from known data on dextrans. The agreement found between the molecular weight averages resulting from GPC and those obtained by other methods justifies the procedure followed. The GPC measurements were performed with dimethylsulfoxide as the elution solvent and deactivated silica gel (Porasil) as the column-filling material.     

The size exclusion chromatography calibration of ‘Mixed-A’ and ‘Mixed-D’ columns using various polymers and compounds: An application to coal-derived materials

This work attempts to obtain the calibration curves of two different size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent by using various standards. Polystyrene (PS) and polymethylmethacrylate (PMMA) standards were used for obtaining calibration curves, and checked against polysaccharide (PSAC) standards, some small aromatic polycyclic standards and miscellaneous polymers. Polystyrenes and polymethylmethacrylates gave identical calibrations while polysaccharides and miscellaneous polymers lay within 1 or 2 min of the polystyrene calibration. Small molecules of mass less than 1000 units lay on or near to the polystyrene calibration lines, with a shift to late elution for the smallest molecules. This shift may be caused by the interaction with the column packing. A sample has been examined by analytical size exclusion chromatography, which was calibrated using polystyrene and polymethylmethacrylate standards. Molecular mass (MM) distributions of the sample have been examined in terms of these calibrations.     

On-line viscometry combined with gel permeation chromatography. I. Instrumental calibration and testing with linear polymers

Gel permeation chromatography (GPC) was combined with flow time measurements on the eluent to provide both the distribution of hydrodynamic volumes and the distribution of intrinsic viscosities in linear polymers. Standard polystyrene samples were used to establish a universal hydrodynamic volume calibration as well as the zone spreading and viscometer transfer line tailing parameters. Viscometry data are particularly helpful in establishing the zone spreading parameters and the calibration curve at very high molecular weights. The results were applied to measurements on samples of linear polybutadiene and polyvinyl acetate. Agreement between values of M _w from GPC with those obtained by light scattering confirmed the universal calibration principle.     

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。     

Problems in the size exclusion chromatography of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) on styragel columns

The molecular weights of poly(N-isopropylacrylamide) (PNIPA), calculated according to polystyrene calibration standards upon the elution of THF on styragel columns, appear to be much lower than their actual values determined using independent approaches. This is likely due to interactions between the nitrogen-containing units of PNIPA polymer chains and the sorbent, so the polymer is eluted in the mode intermediate between exclusion and critical. An effective exclusion mode during the elution of PNIPA on a styragel column can be achieved by using an eluent more polar than tetrahydrofuran (particularly, 1-methylpyrrolidone).     

Determination of molecular weight distribution of cellulose by conversion into tricarbanilate and fractionation

Two samples of cellulose (molecular weight 2.97 × 10⁵ and 1.25 × 10⁵) were transformed into carbanilates (CTC) which were then fractionated by the elution method at a constant composition of the acetone-water elution mixture with the column temperature gradually increasing from ?30°C to 30°C, and by the GPC method in acetone and tetrahydrofuran. Tetrahydrofuran appeared to be a more suitable solvent. The molecular weights of fractions obtained by the elution fractionation were determined by the light-scattering method in tetrahydrofuran. The width of fractions was determined by the GPC method (average M _w/M _n = 1.37); the [η] values and the Mark-Houwink constants (K = 5.3 × 10^-3, a = 0.84) for tetrahydrofuran at 25°C were determined. The calibration curve for the GP method was constructed by means of the fractions thus obtained; it was demonstrated that the universal calibration curve according to Benoit can also be used. It was demonstrated that the molecular weight distribution of cellulose can be conveniently determined by conversion into CTC followed either by the elution fractionation (for preparative purposes) or by fractionation by the GPC method (for analytical purposes).