Polymeric columns for liquid chromatography

Polymeric columns are becoming used more frequently in modern liquid chromatography applications as improvements in polymeric packing materials are realized and as more applications are developed for these materials. Modern polymers have overcome earlier problems associated with their use; higher rigidity now allows them to be used at normal eluent flow rates resulting in faster analyses, and improved synthesis techniques have resulted in efficiencies comparable to the best silica materials, sometimes exceeding 100,000 plates/m. In addition, polymers offer distinct advantages over silica packing for particular applications. Because silica packings are readily degraded by aqueous eluents, they are not always suitable for separations involving ionic species. Polymeric columns are particularly useful in determinations of amino acids, peptides, proteins, organic acids, carbohydrates, and inorganic cations and anions. Polymers are also characterized by exceptional lot-to-lot reproducibility. Reproducibility is often problematic with silica packings, particularly the bonded phases.     

Native and modified alumina,titania and zirconia in normal and reversed-phase high-performance liquid chromatography

Summary Chromatographic properties of silica, alumina, titania and zirconia have been investigated in normal phase mode in the separation of test mixtures of basic, neutral and acidic compounds. In contrast to silica the chromatographic behaviour revealed the basic properties of the alumina, titania and zirconia surfaces. Therefore, separation of basic compounds on these packings seems very promising. Lypophilic packings have been synthesized by modification of titania, zirconia and alumina with organosilanes and polymers and tested for the separation of basic compounds and proteins. High hydrolytic stability of the modified packings was observed during separations with strong alkali and acidic eluents.     

Changes in the pore character of silicas caused by surface bonding and polymer coating

The pore character of packings for liquid chromatography, especially reversed-phase (RPLC) packings, has been studied by means of the nitrogen adsorption method (BET method). Micro-spherical silica gels with 9, 12, 30, 40 and 50 nm average pore diameter have been used as carriers. These silica gels have been modified with monochlorodimethyloctadecylsilane and several polymers (polyoctadecylmethacrylate-methylmethacrylate co-polymer, polyacrylamide gel, polyvinyl alcohol, poly-2-hydroxyethyl-methacrylate). A larger decrease in the specific surface area values was observed in the case of the polymer coating with the polyoctadecylmethacrylate-methylmethacrylate co-polymer compared with the derivatization by silanes or the modification with polymers without C18-groups. A new approach has been suggested to explain some questions concerning the interpretation of the data obtained during the measurements of the pore characteristics of the derivatized packings. An attempt has been made to reveal peculiarities connecting values of the measured surface of RP-packings with the specific surface area values of the initial silica, as well as with the chromatographically accessible surface.     

High Efficiency Ligand Exchange Chromatography of Amino Acid Enantiomers

Abstract

We obtained resolution of α-amino acids with an efficiency in the range of 10 000–25 000 plates/m and a selectivity factor in the range of 1.12–2.5 with packings easily prepared by adsorption of chiral polymers on a chromatographic silica.     

A Queous Exclusion Chromatography

Abstract

The exclusion chromatography of water-soluble polymers has been a field of intense activity in recent years. Although polysaccharide gels like Agarose and Sephadex have long been used for the size separation of proteins (“gel filtration”), only the advent of new hydrophilic column packings could lead to the widespread application of aqueous GPC to syllthetic polymers. These new substrates are produced with the mechanical strength and the uniformity and control of both particle- and pore-size distributions requisite to the packing of high-efficiency columns. Such columns offer good separation of species of different molecular weight (MW) along with minimal band-spreading, and so car? provide, in principle, detailed and accurate MW distribution data coupled with short analysis times. MWD accuracy and assay speed - relatively unimportant in most bio-chemical research laboratories - are paramount considerations in the industrial laboratory involved with synthetic water-soluble polymers.     

Reactivity Ratios for Divinylbenzene and Ethylene Glycol Dimethacrylate Copolymerizations with Styrene and Methyl Methacrylate

The free radical copolymerization of styrene and other vinyl monomers to produce cross-linked, network polymers is of technological importance in the production of ion-exchange resins, packings for gas-liquid and gel permeation chromatography, cross-linked latex polymers, and other products. The principal multifunctional cross-linking monomers which are used in this connection are ethylene glycol dimethacrylate and divinylbenzenes, and accurate values for reactivity ratios in their reactions with bifunctional monomers are essential for the design of copolymerization processes and products.

Wiley and co-workers have reported reactivity ratios for the copolymerizations of these monomers with styrene and with methyl methacrylate [1]. In these studies the reactivity ratios were calculated from the raw data using a graphical “method of intersections” [2]. In this procedure the differential copolymer equation is put into the form     

Synthesis and characterization of side chain liquid crystalline polymers exhibiting cholesteric and blue phases

A series of cyclosiloxane-based cholesteric liquid crystalline (LC) polymers were synthesized from a cholesteric LC monomer cholest-5-en-3-yl(3β) 4-(2-propenyloxy)benzoate and a nematic LC monomer butyl 4-[4-(2-propenyloxy)benzoxy]benzoate. All the polymers exhibit thermotropic LC properties and show cholesteric phases. Most of the polymers display four types of phase transition behaviour corresponding to glass transition, melting point, cholesteric phase-blue phase transition and clearing point. The mesophase temperature range of the blue phases are as broad as 20°C. The blue phase was confirmed by the apperance of planar textures and cubic packings. With an increase of non-chiral component in the polymers, the clearing point decreases slightly, while the glass transition and melting temperatures change little. In the reflection spectra of the polymer series the reflected wavelength broadens and shifts to longer wavelength with increase of the non-chiral component in the polymer systems, suggesting that the helical pitch P lengthens.     

高效液相色谱用硅质填料的进展

 对高效液相色谱用硅质填料的进展情况做了全面的评述。介绍了硅质填料的制备及化学修饰 ,评价了硅胶表面的物理表征 ,概括了硅质填料在高效液相色谱中的应用 ,并对我国的硅质填料前景进行了展望。     

A New Packing for Aqueous Size Exclusion Chromatography Polyvinylpyrrolidone-Coated Silica

Abstract

Adsorption of polyvinylpyrrolidone on silica in aqueous medium is studied. Adsorption isotherms, thermogravimetry and elementary analysis show that a complete surface coverage is reached with large pore microbeads. The coating stability and its ability to prevent non-steric effects when used as packing in exclusion chromatography are demonstrated. Four different pore size packings were prepared for chromatographic evaluations. It is shown that water soluble polymers like polyethylene oxide, polyvinylalcohol, polyacrylamide and hydroxyethylcellulose can be chromatographied in pure water according to the steric exclusion mechanism.     

Direct Resolution of Enantiomers in Column Liquid Chromatography

Abstract

Important progress has been performed during the ten past years, in the direct resolution (without derivatization) of enantiomers by column liquid chromatography. Generally chiral packings proceeding from natural or synthetic optically active polymers are used. Complete resolutions of hole families of chiral solutes is obtained in systems involving a steric locking interaction (charge transfer between aromatic substituents, crown ether cavity, crowded complexes with metal ions). For analytical purposes an other proraising way is the use of a classical packing and a chiral mobile phase.     

Separation of polystyrenes by means of open tubular capillary chromatography

Simulating polymer separation in flow-through channels of monolithic columns, separation of a mixture of polystyrene standards was investigated using open tubular capillary column of 2 μm inner diameter. High column efficiency was observed for polymers of molar mass ranged from few tens to few hundred kDas. Column efficiency significantly decreased for polymers with molar mass larger than 500 kDa nevertheless preserving value of few tens of thousands theoretical plates. Calibration curve observed for open capillary column is rather steep and can be well described by simple equation without quadratic term. In spite of low selectivity, capillary columns were able in separating wide range of polystyrene standards due to column high efficiency and in such a way supported an idea of hydrodynamic mechanism of polymer separation in flow-through channel of monolithic packings.     

Performance of metal complex substituted polysiloxanes in capillary electrophoresis and capillary electrochromatography

Two novel polysiloxanes containing the metal complex, Co(TACN)(3+)2 (TACN= 1,4,7-triazacyclononane) were used as coatings for capillary electrophoresis (CE) and capillary electrochromatography (CEC). Through crosslinking and covalent bonding, the positively charged polymers were bonded to silica supports. In both CE and CEC, these coatings exhibited strong, pH-independent, and anodic electroosmotic flow (EOF), and had excellent long-term stability. Successful separations of aromatic acids were achieved in CE. In CEC, separation of alkylbenzenes (7 min) and basic compounds (20 min) was achieved with higher resolving power than conventional octadecyl silica packings. These polymers represent a new class of coatings for CE and CEC that generate pH-independent EOF.     

Selectivity in reversed-phase separations Influence of the stationary phase

The selectivity difference between 15 different stationary phases was measured using a large number of analytes at 2 or 3 different pH values (3, 7 and 10) with acetonitrile and methanol as the mobile phase modifiers. The packings discussed include standard C(8) and C(18) packings, packings with embedded polar groups, a phenyl packing, a pentafluoro-phenyl packing, an adamantylethyl packing and others. The major selectivity differences observed are discussed in detail. Specific effects such as pi-pi interactions on phenyl packings or hydrogen-bond interactions on phases with embedded polar groups are confirmed.     

Self-assembly of spherical particles on an evaporating sessile droplet

Particles adsorbed on the surface of a droplet form three-dimensional packings when the droplet evaporates. We study the final packings when the liquid droplet is attached to a solid substrate. In contrast to a droplet evaporating away from a substrate, here the final packings are highly dependent on both the number of particles and the contact angle between the droplet and the surface. Simple geometrical constraints quantitatively determine the parameter regions that particular packings can form.     

凝胶渗透色谱多孔硅胶吸附问题的研究

本文以端基为羟基的聚二甲基硅氧烷为测试样品,甲苯为淋洗液,研究了凝胶色谱柱填料多孔硅胶的表面羟基含量等与吸附效应的关系。说明采用对硅胶进行表面处理和在淋洗液中加入吸附抑制剂的方法,不能避免吸附。建议采用端基封闭剂(如三甲基氯硅烷)处理聚合物的活性端基——羟基的方法,解决吸附问题。     

Influence of the Amount of Bonded Non-Polar Phase and of the Length of Attached Alkyl Chains on Retention Characteristics of Silica-Based Sorbents for Reversed-Phase High Performance Liquid Chromatography

Abstract

The retention characteristics of two sets of chemically bonded non-polar silica packings with a high surface concentration of functional groups have been compared in the reversed-phase mode of liquid chromatography: (i) the conventional packings prepared by chemical modification with trimethylsilyl, heptyl, dodecyl and octadecyl groups, and (ii) mixed-phase materials where differences in the amount of organic bonded phase were achieved by bonding octadecyl and trimethylsilyl groups in different proportions. The retention data of two homologous series of solutes show that these two classes of packings are distinctly different; in particular, the capacity factors and selectivities are always higher on the mixed-phase bonded silica packings at the same percentage of carbon.     

Some properties of three-periodic sphere packings

Some properties of sphere packings are reviewed. Candidates for the least-dense packings of one kind of sphere for different coordination numbers are identified and described. Some topological properties of sphere packing nets are also described.     

Superficially porous silica microspheres for fast high-performance liquid chromatography of macromolecules

Very fast reversed-phase separations of biomacromolecules are performed using columns made with superficially porous silica microsphere column packings ("Poroshell"). These column packings consist of ultra-pure "biofriendly' silica microspheres composed of solid cores and thin outer shells with uniform pores. The excellent kinetic properties of these new column packings allow stable, high-resolution gradient chromatography of polypeptides, proteins, nucleic acids, DNA fragments, etc. in a fraction of the time required for conventional separations. Contrasted with <2-microm non-porous particles, Poroshell packings can be used optimally with existing equipment and greater sample loading capacities, while retaining kinetic (and separation speed) advantages over conventional totally porous particles.     

Characterization of Organomagnesium Modified Kel-F Polymers as Column Packings

Abstract

The reactivity of Kel-F (polychlorotrifluoroethylene) with a variety of Grignard reagents and the HPLC separation capability of these modified packings have been compared. Columns packed with long alkyl (C-8 or C-18) modified Kel-F 6061 supports had poor lifetimes while short alkyl (CH₃) modified fluoropolymers did not produce effective separations. Aromatic modified Kel-F 6300 polymers, particularily phenyl supports, were both pressure stable and useful for the retention of various functionalized aromatics as well as the separation of simple drug mixtures.     

分离尿激酶的胍基型亲和色谱填料研究

尿激酶的精制一般使用亲和色谱法［’－‘ｊ．目前实际使用和文献报道最多的填料是在 ＳｅＰｈａｒｏｓｅ上键合对氨基苯眯（ｐ－ＡＢＺ）制得的［‘ｊ．这种填料分高效果较好,但机械强度不高,只能用于常压色谱,而且寿命较短．前文［‘１报道了用 ＳｅＰｈａｒｏｓｅ和聚甲基丙烯酸环氧丙酯微球为基质, Ｐ－ＡＢＺ为配基分离尿激酶的亲和色谱填料的对照研究．本文报道以含肥基的有机小分子为配基,ＳｅＰｈａｒｏｓｅ及两种聚甲基丙烯酸环氧丙酯微球为基质的分离尿激酶色谱填料的合成和性能试验．发现肥基己酸和精氨酸为配基的亲和色谱…