Recent progress in carbohydrate separation by high-performance liquid chromatography based on size exclusion

Since the introduction of stationary phases based on microparticulate porous silica and polymeric sorbents, rigid and semi-rigid, size-exclusion chromatography (SEC) has become established as a form of high-performance liquid chromatography. In recent years, there have beeen revolutionary developments in detection systems for high-performance SEC, which have placed the use of the method for the determination of molecular-size and molecular-weight distributions of polymers on a sound theoretical basis andincreased the range of information on molecular characteristics that can be retrieved from SEC data. This review surveys these changes in SEC systems and their application to the separation and molecular-weight distribution analysis of carbohydrates.     

Thin-layer chromatography of pitch and a petroleum vacuum residue. Relation between mobility and molecular size shown by size-exclusion chromatography

A coal tar pitch and a petroleum vacuum residue have been separated by TLC using pyridine, acetonitrile, toluene and pentane to develop the chromatograms. The bands of material detected were recovered in 1-methyl-2-pyrrolidinone (NMP) solvent and examined by size-exclusion chromatography (SEC) in NMP eluent. The relation between elution time in SEC and mobility on the TLC plate indicated that molecular size increased steadily with increasing immobility on the plate. This relation was reinforced by UV fluorescence spectroscopy in that the fluorescence moved to longer wavelengths with increasing immobility. The molecular size of the material excluded from the porosity of the SEC column remains undefined; some excluded material was found in all of the fractions from both samples. The valley of zero intensity separating the retained material from the excluded material may suggest a change of structure from near-planar in the retained region to three-dimensional in the excluded region.     

Porous polystyrene packings: Characterization through pore structure determination

Summary In this paper the pore structure of several porous polystyrene pearls as used in chromatography is investigated by N2-adsorption and by the inverse size exclusion chromatography (SEC) of Halász. The results indicate that only the inverse SEC measurements give valuable information about the polystyrene packing materials although the obtained pore size distribution is too broad. Reasons for the shortcomings of inverse SEC are discussed.     

Thermodynamic equilibrium of the solute distribution in size-exclusion chromatography

Our understanding of the nature of solute retention in size-exclusion chromatography (SEC) is predicated upon an equilibrium, entropy-controlled, size-exclusion mechanism. The entropic nature of the separation depends, in turn, upon the solute distribution coefficient (K(SEC) being at (or close to) thermodynamic equilibrium. Classic experiments to confirm this assumption were performed over thirty years ago. Here, we combine information obtained from both flow and static mixing SEC experiments to show that the solute distribution in SEC is in thermodynamic equilibrium over a molar mass range extending one order of magnitude higher than previously measured (from 2 x 10(3) to 1.1 x 10(6) Da) using crosslinked polystyrene packing material of identical pore size (10(4) A). The differences between our observations and previous ones conducted over three decades ago are ascribed, principally, to advances in stationary phase synthesis and column technology for SEC in particular and, secondarily, to improvements in the performance of the various instrumental components of liquid chromatographic systems in general.     

Evaluation of size-exclusion chromatography and size-exclusion electrochromatography calibration curves

Size-exclusion chromatography (SEC) and size-exclusion electrochromatography (SEEC) are chromatographic techniques used to determine molecular mass (weight) distributions (MWD) of polymers. One important step in the data treatment to derive MWD parameters is the modelling of the calibration curves. The calibration curves applied in SEC and SEEC are generally not linear. In this study the modelling of calibration curves is being examined. Different polynomial models have been evaluated and compared, not only for model fit but also for their predictive properties. It was found that sometimes a straight line and sometimes a third-order polynomial model were best. The best model across the effective range (also called linear range) is not always found to be a straight line. The SEEC curves were found to have considerably higher prediction errors than the SEC ones. Reduction of the number of calibration standards to five or six did not greatly affect the predictive properties of the calibration curves, neither in SEC nor in SEEC.     

多检测GPC技术在高分子表征中的应用

多检测ＧＰＣ／ＳＥＣ在高分子表征中可获得比普通单检测ＧＰＣ丰富得多的重要信息,因而受到学术界和工业界的广泛重视。详细介绍了ＧＰＣ／ＲＩ／ＲＡＬＬＳ／ＤＶ多检测技术的检测原理,并介绍了应用实例。     

Porous crosslinked spherical resins for diversified applications: packing materials for size exclusion chromatography

Improvements in the synthesis of porous polymers for different applications have been carried out in our laboratory. Beads of poly(styrene-co-divinylbenzene) with morphology adequate to the application at hand were prepared. Packing materials for size exclusion chromatography (SEC) weve prepared by single-step swelling and polymerization (SSWP) and by modified suspension polymerization (MSP). High values of exclusion limit (10⁶ and 8.0x10⁶) were attained for SEC columns packed with poly(styrene-co-divinylbenzene) synthesized using high proportions of polystyrene, as porogen agent and divinylbenzene. The maximum values of exclusion limits were attained for SEC columns packed with beads prepared by SSWP method.     

Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT

The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.     

The obstruction factor in size-exclusion chromatography. 1. The intraparticle obstruction factor

We report the first of a series of studies on the obstruction factor γ in size-exclusion chromatography (SEC). Here, using narrow dispersity polymer standards we examine how the intraparticle obstruction factor γ(p) depends individually on a number of analyte properties, column characteristics, and user-defined parameters. Far from being constant, γ(p) is seen to vary with analyte molar mass and solvent, as well as with the pore size and particle size of the column packing material, sometimes in seemingly counterintuitive manner. Over the limited temperature range accessible to our equipment, however, no statistically significant change in γ(p) with temperature was discovered. The results presented should be applicable to forms of packed column chromatography other than SEC. The latter technique, however, presents a convenient test bed for quantitative determination of the obstruction factor, due to minimized sorptive mass transfer and longitudinal diffusion contributions to band broadening in most forms of SEC.     

Size-exclusion chromatography (SEC) of branched polymers and polysaccharides

Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight.     

Fractionation of ethylene/1‐pentene copolymers using a combination of SEC‐FTIR and SEC‐HPer DSC

The short chain branching distribution (SCBD) and thermal properties of ethylene/1‐pentene copolymers were studied using SEC‐FTIR and SEC‐HPer DSC. The copolymers, synthesized with Cp₂ZrCl₂/MAO, were fractionated using size exclusion chromatography (SEC). The infrared analysis of the fractions showed that the copolymers had—on average—higher 1‐pentene concentration in the low molecular weight range. Furthermore, the thermal properties of the SEC deposits of these copolymers on a Germanium disc were studied using high performance differential scanning calorimetry (HPer DSC). Single SEC separations were used to accumulate fractions in the microgram range that were directly analyzed with regard to their thermal properties, thus allowing us to study SCBD as well as thermal behavior simultaneously. When these fractions (with masses ranging from 10–80 μg) were analyzed using HPer DSC, good melting and crystallization temperature distributions were obtained, proving that HPer DSC can be used as a complementary method to SEC‐FTIR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2956–2965, 2007     

Dissolution of a surfactant-containing active porous material

We have studied the imbibition and dissolution of a porous material in two separate scenarios: (1) when the porous material contains a surfactant powder and (2) when the porous material is dissolved in a surfactant solution. We show that the dissolution kinetics in both scenarios is significantly affected by the presence of the surfactant and results in an increase in the characteristic imbibition time of the porous material, which can be well understood in the framework of the classical law of capillarity. Slowing of the imbibition kinetics was found to be affected by a modification of the liquid wetting properties, but is also affected by a variation in the solubility of the porous material in the presence of the surfactant. Furthermore, there is a depletion effect of the surfactant inside the rising liquid, which is in good agreement with previous work and theoretical predictions.     

Characterization of branched ultrahigh molar mass polymers by asymmetrical flow field-flow fractionation and size exclusion chromatography

The molar mass distribution (MMD) of synthetic polymers is frequently analyzed by size exclusion chromatography (SEC) coupled to multi angle light scattering (MALS) detection. For ultrahigh molar mass (UHM) or branched polymers this method is not sufficient, because shear degradation and abnormal elution effects falsify the calculated molar mass distribution and information on branching. High temperatures above 130 °C have to be applied for dissolution and separation of semi-crystalline materials like polyolefins which requires special hardware setups. Asymmetrical flow field-flow fractionation (AF4) offers the possibility to overcome some of the main problems of SEC due to the absence of an obstructing porous stationary phase. The SEC-separation mainly depends on the pore size distribution of the used column set. The analyte molecules can enter the pores of the stationary phase in dependence on their hydrodynamic volume. The archived separation is a result of the retention time of the analyte species inside SEC-column which depends on the accessibility of the pores, the residence time inside the pores and the diffusion ability of the analyte molecules. The elution order in SEC is typically from low to high hydrodynamic volume. On the contrary AF4 separates according to the diffusion coefficient of the analyte molecules as long as the chosen conditions support the normal FFF-separation mechanism. The separation takes place in an empty channel and is caused by a cross-flow field perpendicular to the solvent flow. The analyte molecules will arrange in different channel heights depending on the diffusion coefficients. The parabolic-shaped flow profile inside the channel leads to different elution velocities. The species with low hydrodynamic volume will elute first while the species with high hydrodynamic volume elute later. The AF4 can be performed at ambient or high temperature (AT-/HT-AF4). We have analyzed one low molar mass polyethylene sample and a number of narrow distributed polystyrene standards as reference materials with known structure by AT/HT-SEC and AT/HT-AF4. Low density polyethylenes as well as polypropylene and polybutadiene, containing high degrees of branching and high molar masses, have been analyzed with both methods. As in SEC the relationship between the radius of gyration (R(g)) or the molar mass and the elution volume is curved up towards high elution volumes, a correct calculation of the MMD and the molar mass average or branching ratio is not possible using the data from the SEC measurements. In contrast to SEC, AF4 allows the precise determination of the MMD, the molar mass averages as well as the degree of branching because the molar mass vs. elution volume curve and the conformation plot is not falsified in this technique. In addition, higher molar masses can be detected using HT-AF4 due to the absence of significant shear degradation in the channel. As a result the average molar masses obtained from AF4 are higher compared to SEC. The analysis time in AF4 is comparable to that of SEC but the adjustable cross-flow program allows the user to influence the separation efficiency which is not possible in SEC without a costly change of the whole column combination.     

Pig Bone Derived Hierarchical Porous Carbon‐Supported Platinum Nanoparticles with Superior Electrocatalytic Activity Towards Oxygen Reduction Reaction

Hierarchical porous carbon (HPC) with nitrogen doped three dimension open macropore structure was prepared from pig bone, and applied for the support material for platinum nanoparticle (Pt NP) electrocatalyst. Compared with carbon black supported Pt NP electrocatalysts, the Pt/HPC exhibited larger electrochemical active surface area and enhanced catalytic properties for the oxygen reduction reaction (ORR) in terms of on‐set potential, current density, mass activity and stability. The superior catalytic activity is mainly attributed to the high surface area, hierarchical porous structures and the nitrogen‐doped surface properties of the HPC, indicating it is a promising support material for the ORR electrocatalysts.     

Separation of water-soluble polymers using capillary-channeled polymer fiber stationary phases

Chromatographic separations of synthetic and natural polymers are usually affected by a size exclusion chromatography (SEC) mechanism. Although SEC is a proven method of separation based on hydrodynamic size, a chromatographic method based solely on chemical interactions would present certain advantages. This laboratory has been investigating the use of capillary-channeled polymer (C-CP) fibers as stationary phases in HPLC for the separation of biomacromolecules. C-CP fibers allow highly efficient fluid transport and an amorphous surface structure, minimizing mass transfer effects commonly associated with porous, packed-bed technologies. Choice of the base fiber identity allows flexibility in the potential types of solute-surface interactions. Two water-soluble polymers, glycolic acid ethoxylate 4-nonylphenyl ether, and poly(4-vinylpyridine hydrochloride), were used as test solutes because of their similarities to polymers of interest in the consumer products industry. SEC separation of this pair was not possible due to the similarities in hydrodynamic size. Poly(ethylene terephthalate), polyester and nylon-6 C-CP fibers were evaluated as stationary phase materials. The former was found to offer superior chromatographic separations and recoveries when operating under what would be considered to be typical RP separation conditions: a flow rate of 1?mL/min and gradient of 0-100% H(2)O/ACN with 0.06% TFA over 5?min.     

The development of porcelain foams lighter than water for heat isolation application

In this study, technological and heat isolation properties of porous ultra-lightweight porcelain foams were investigated. Traditional construction materials such as brick show good durability against environmental conditions. Bricks are also a good alternative compared to pumice blocks and autoclaved aerated concrete which are largely used as construction materials. Bricks are also more economical than the other construction materials. But they also have poorer thermal insulation properties. Among the construction material, XPS shows the best heat isolation properties. XPS (extruded polystyrene foam) is a polymeric material. Although XPS shows best heat insulation property, it easily flames. The aim of this study is developing porous porcelain isolation materials lighter than water by using a replication method and relatively better thermal isolation properties than the other construction materials.

     

Novel polystyryl resins for size exclusion chromatography

New size exclusion chromatography (SEC) resins based on a crosslinker having independent vinyl groups have been produced and compared with SEC resins based on divinylbenzene-55 (DVB). 1,2-Bis(p-vinylphenyl)ethane (p,p-BVPE) and its meta-isomers were suspension-copolymerized with p-methylstyrene in the presence of different porogens to give particles of about 5 μm average diameter. The porous particles were slurry-packed into stainless steel columns for SEC evaluation. Calibration curves were obtained using narrow disperse polystyrene standards with molecular weights ranging from 580 to 3,040,000. The calibration curves for the new BVPE resins covered wider useful molecular weight ranges than those for comparable divinylbenzene resins. Particle size, surface morphology and the properties of pores were studied using a Coulter Multisizer II, scanning electron microscopy, nitrogen adsorption, and mercury porosimetry. © 1994 John Wiley & Sons, Inc.     

Characterization of implant device materials using size-exclusion chromatography with mass spectrometry and with triple detection

A more complete understanding of the raw materials used for making implant device materials becomes increasingly important in the medical device industry. Often such detailed information requires utilization of a combination of analytical techniques. In this work, we characterize a poly(dimethyl siloxane) (PDMS) material using on-line size exclusion chromatography (SEC) with electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) techniques. Here, we obtain detailed molecular compositional information such as repeat units, end group chemistry, and identification of impurities in both the high and low mass range. SEC with light scattering, viscosity, and refractive index detection (triple detection) is used to obtain information on a small quantity of high mass impurity that was undetected by both SEC-ESI and MALDI MS techniques. SEC with triple detection measures absolute molecular weights and molecular weight distributions. We compare average molecular weight values of the implantable device polymer obtained by SEC with triple detection, SEC-ESI, and SEC-MALDI MS techniques.     

A capillary gas chromatographic column with a porous layer based on a mesoporous material

A procedure for synthesizing an MSM-41-type mesoporous mesophase material (MMM) layer, that is, a layer of a solid porous material with a regular arrangement of nanoscale calibrated pores and a unified geometry, on the inner wall of a capillary column was developed. Because of the high specific surface area of silica, capillary columns with a porous MMM layer on the basis of silica allow the amount of samples introduced to be increased by an order of magnitude compared with the known capillary porous-layer columns. An example of the separation of light hydrocarbons is described. The properties of columns with MMM porous layers are discussed.     

Molar mass characterization of cationic methyl methacrylate-ethyl acrylate copolymers using size-exclusion chromatography with online multi-angle light scattering and refractometric detection

Size-exclusion chromatography (SEC) combined with online multi-angle light scattering (MALS) and refractometric (RI) detection has been employed for the molar mass characterisation of water-insoluble cationic methyl methacrylate-ethyl acrylate copolymers (Eudragit RS and RL). Due to their positive charge, cationic polymers are particularly difficult to separate on a SEC column, in worst cases being completely adsorbed on the oppositely charged packing material. This work has examined how a careful addition of salt (LiCl) to the copolymer solution in ethanol decreases the electrostatic interactions, clearly seen as a decrease in elution volume from the SEC column as well as an improved recovery. At a certain level of ionic strength, typically about 50 mM, the copolymer recovery from the SEC column reached 100% and molar mass distributions corresponding to the complete sample could be obtained. The combined MALS/RI detection gives the opportunity to measure the absolute molar mass independent of recovery and retention. Thus, in this study, it turned out to be a favourable tool for tracing the changes in elution behaviour of the charged copolymer as the ionic strength was increased.