Chromatography of aromatic compounds on anion-exchange resins

Complex mixtures of aromatic compounds can be rapidly separated on anion-exchangers in the acetate form with acetic acid as eluent and determined automatically by recording the absorbance in the ultraviolet. Carboxylates are separated by ion-exchange. Hydrogen bonds between non-disso-ciated acids and the counter-ions influence the distribution coefficients. Hydrogen-bonding with the resin has a marked effect on the sorption of solutes containing phenolic protons. Intramolecular hydrogen-bonding depresses their sorption. Hydrophobic interactions have a predominant influence with hydrocarbons and with phenolic compounds containing non-polar aliphatic substituents. The relative importance of these interactions increases with a decreased ion-exchange capacity of the resin.     

Automated chromatography of uronic acids on anion-exchange resins

An automatic system is described for the determination of various uronic and biouronic acids after chromatographic separation on an anion-exchange column. Elution is carried out with sodium acetate or acetic acid, and the colors developed with carbazole and after oxidation with chromic acid are determined in a multichannel photometer and recorded continuously.     

Automatic chromatography of hydroxy acids on anion-exchange resins

Hydroxy acids are separated on an anion-exchange column and determined automatically by three colorimetric methods: chromic acid oxidation, periodate oxidation and the carbazole reaction. The simultaneous application of three methods facilitates both identification and determination.     

Separation of aromatic compounds on pellicular anion-exchange resins

Aromatic compounds including phenols, carboxylic acids and aldehydes, can be rapidly separated on pellicular anion-exchange resins in the acetate form by elution with a sodium acetate solution. Like the aromatic carboxylic acids, hydroxybenzaldehydes are held as counter ions in the resin. The affinity of the resin for corresponding anions as well as that for sorbed non-electrolytes is largely influenced by the aromatic ring and non-polar aliphatic substituents. Formation of hydrogen bonds between the resin and phenolic groups is less important.     

Screening of Dowex® anion-exchange resins for invertase immobilization

Commercial yeast invertase (Bioinvert^®) was immobilized by adsorption on anion-exchange resins, collectively named Dowex^® (1×8:50–400, 1×4:50–400, and 1×2:100–400). Optimal binding was obtained at pH 5.5 and 32°C. Among different polystyrene beads, the complex Dowex-1×4–200/invertase showed a yield coupling and an immobilization coefficient equal to 100%. The thermodynamic and kinetic parameters for sucrose hydrolysis for both soluble and insoluble enzyme were evaluated. The complex Dowex/invertase was stable without any desorption of enzyme from the support during the reaction, and it had thermodynamic parameters equal to the soluble form. The stability against pH presented by the soluble invertase was between 4.0 and 5.0, whereas for insoluble enzyme it was between 5.0 and 6.0. In both cases, the optimal pH values were found in the range of the stability interval. The K _m and V _max for the immobilized invertase were 38.2 mM and 0.0489 U/mL, and for the soluble enzyme were 40.3 mM and 0.0320 U/mL.     

Phase separation in the formation of hollow particles by suspension polymerization for divinylbenzene/toluene droplets dissolving polystyrene

Phase-separation behavior within polymerizing divinylbenzene/toluene droplet dissolving polystyrenes (PS) was investigated to clarify the formation mechanism of the hollow polymer particles by suspension polymerization. No hollow particles were obtained at a low content of low-molecular-weight PS where phase separation occurred at high conversion. On the other hand, hollow particles were obtained at a high content of high-molecular-weight PS where phase separation occurred at low conversion. The phase separation in an early stage of the polymerization, which was promoted by the presence of PS and cross-links of polydivinylbenzene, was a key factor for the formation of the hollow structure.     

Influence of aromatic compounds in sugar chromatography on anion-exchange resins

In sugar separations by partition chromatography on anion-exchange resins in aqueous ethanol, phenolic compounds are eluted within the same range as sugars and interfere when non-specific detectors are used. The simultaneous application of the orcinol method for sugars and an ultraviolet-detector for the aromatic compounds makes it possible to determine both types of compounds in the same chromatographic run.     

Separation of sugar derivatives by partition chromatography on anion-exchange resins

The separation of a number of sugar derivatives such as methyl, ethyl, benzyl, hydroxyethyl erners and various glycosides has been studied. An efficient separation of most species was obtained in 94% ethanol using an anion-exchange resin in its sulfate form. The eluate concentration was determined automatically using the orcinol method.     

Equilibrium and calorimetric study of the hydration of anion-exchange resins

The adsorption of water vapour on anion-exchangers of various degrees of cross-linking ( x 2, x 4, x 8, x 10) and in different ionic forms (Cl(-), Br(-), I(-)) was studied by the isopiestic technique. The calculated integral free-energy changes were independent of the degree of cross-linking of the resins. With increase in the number of adsorbed water molecules the free-energy functions approached limiting values which were characteristic for the counter-ions. The free-energy change was combined with the enthalpy of water sorption (obtained from direct calorimetric measurements) to obtain the entropy change due to the water uptake. Both the enthalpy and the entropy functions indicated the existence of several processes during the adsorption of water, among which the most relevant are hydration, swelling of the matrix, and dilution of the internal electrolyte of the ion-exchanger.     

Adsorption of some metals on anion-exchange resins from potassium thiocyanate solutions

The adsorption of a number of metals on Dowcx-I from potassium thiocyanate solutions has been studied. Distribution coefficients were measured as a function of thiocyanate concentration for zinc, cobalt, cadmium, scandium, and silver. Some separations of metals employing thiocyanate as the complexing agent are reported.     

Effect of the acylating agent on the selectivity of anion-exchange resins and separation efficiency

Anion-exchange resins have been prepared by a two-step process that comprises the acylation of polystyrene/divinylbenzene (PS/DVB) with 50% crosslinking and subsequent amination with trimethylamine. The spacer arm between the quaternary ammonium functionality and the polymer backbone in these resins contains three, four, or five carbon atoms. An increase in the spacer arm improves the separation efficiency, affects the selectivity, and produces more symmetric peaks.     

Effect of the content of divinylbenzene in ion-exchange resins on the chromatographic separation of alpha-cyclodextrin and glucose

In the chromatographic separation of alpha-cyclodextrin and glucose, the parameters relating to the adsorption equilibria and rate processes of the solutes were evaluated for the sodium forms of cation-exchange resins with contents of divinylbenzene (DVB) of 2, 4, 6 and 8%. By using these parameters, the chromatograms of the solutes were then calculated. It is concluded that the resin with 6% DVB is most suitable for the chromatographic separation of the solutes on a preparative scale.     

Application of micropellicular poly-styrene/divinylbenzene stationary phases for high-performance reversed-phase liquid chromatography electrospray-mass spectrometry of proteins and peptides

Summary Short columns packed with highly crosslinked 2.3 μm poly-styrene/divinylbenzene (PS/DVB) particles were used for rapid and efficient separation of proteins and peptides by reversed-phase high-performance liquid chromatography at elevated temperatures. Enhancement of the diffusivities of the sample components at elevated temperatures together with the short diffusion pathlength with the micropellicular polymeric stationary phases were responsible for high efficiency, high speed of analysis, and short column regeneration times. Underivatized PS/DVB beads as well as PS/DVB microspheres which have been modified with polyvinylalcohol or octadecyl chains on the surface were synthesized, employed, and compared to HY-TACH-C18, a commercially available micropellicular octadecyl-silica stationary phase, for the separation of proteins, octapeptides and tryptic protein digests. Highest performance was obtained with the silica- and PS/DVB-based octadecyl stationary phases, which exhibited similar column efficiencies but different selectivities for proteins and peptides. The minimum detectability at 214 nm and the maximum loading capacity for ribonuclease A using analytical 30×4.6 mm I.D. columns were 10 ng (0.6 pmol) and 1 μg, respectively. Finally, reversed-phase HPLC with a 60×2 mm I.D. narrow-bore column packed with micropellicular octadecyl PS/DVB was coupled successfully to electrospray mass spectrometry at a flow-rate of 0.15 mL min⁻¹ and on-line full-scan mass spectra for molecular mass determination and identification of proteins in the lower picomol range were obtained.     

Retention of anions on silica-based metalloporphyrin stationary phases.

The silica-based Fe(III)-protoporphyrin and Zn-tetraphenylporphyrin stationary phases were examined for the HPLC separation of anions. The retention of nine common inorganic anions as well as benzoate anion (BA) and its hydroxy analogues (HBA) was examined using tartrate, acetate, and succinate eluents. The retention factors of inorganic anions on the FeProP stationary phase were in the order Cl- < NO3- < ClO4- < I- < SCN- and for organic anions benzoate < p-hydroxybenzoate < m-hydoxybenzoate < o-hydroxybenzoate. The retention factors of organic anions examined for a ZnTPP column were in the order p-HBA < m-HBA < BA < o-HBA.     

Controlled anionic synthesis of star‐shaped polystyrene by the incremental addition of divinylbenzene

Star polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental‐addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one‐shot addition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 870–878, 2005     

Chromatographic evaluation of reversed-phase/anion-exchange/cation-exchange trimodal stationary phases prepared by electrostatically driven self-assembly process

This work describes chromatographic properties of reversed-phase/cation-exchange/anion-exchange trimodal stationary phases. These stationary phases were based on high-purity porous spherical silica particles coated with nano-polymer beads using an electrostatically driven self-assembly process. The inner-pore area of the material was modified covalently with an organic layer that provided both reversed-phase and anion-exchange properties while the outer surface was coated with nano-sized polymer beads with strong cation-exchange characteristics. This design ensured spatial separation of the anion-exchange and the cation-exchange regions, and allowed reversed-phase, anion-exchange and cation-exchange retention mechanisms to function simultaneously. Chromatographic evaluation of ions and small molecules suggested that retention of ionic analytes was influenced by the ionic strength, pH, and mobile phase organic solvent content, and governed by both ion-exchange and hydrophobic interactions. Meanwhile, neutral analytes were retained by hydrophobic interaction and was mainly affected by mobile phase organic solvent content. Depending on the specific application, selectivity could be optimized by adjusting the anion-exchange/cation-exchange capacity ratio (selectivity), which was achieved experimentally by using porous silica particles with different surface areas.     

Ageing of thermosets based on tung oil/styrene/divinylbenzene

New thermoset polymers prepared by cationic co-polymerization of tung oil with styrene and/or divinylbenzene were evaluated at different times after their preparation. The changes in the properties were correlated with the composition of the copolymers. The action of atmospheric oxygen on the fatty acid unsaturations produced chemical changes in these polymers, which affected the properties of the cured materials. These changes were analyzed by FTIR, dynamic mechanical properties and mechanical testing. An increase in the modulus with time for all the analyzed samples was observed, as well as a large effect on the glass transition temperature and, consequently, in the shape memory properties.