Prediction of the net retention volumes in gas chromatography using porous polymers coated with different stationary phases

Summary A new expression which permits the prediction of the net retention volumes in gas chromatography with column packings of coated porous polymers is reported. The porous polymers Chromosorb 101 and Chromosorb 102 were used as supports and squalane, Ethofat and Carbowax 20M as stationary phases at three different column temperatures of 80°C, 100°C and 150°C. Several organic compounds of various polarity were used as test compounds and the net retention volumes, V_Ntheor, have been calculated according to this new expression. The V_Ntheor values were compared with the experimental net retention volumes, V_Nexp, and it was found that the difference between these two values is dependent on the type of compound and column packing. Nevertheless, the elution order could be predicted in most cases.     

HPLC of synthetic polymers characterization of polystyrenes by high performance precipitation liquid chromatography (HPPLC)

Summary The advantages and disadvantages of high performance precipitation liquid chromatography have been demonstrated for polystyrene homopolymers. Depending on the mobile phase composition at the dissolution point of the polymeric sample and surface properties of the stationary phase, elution is governed either by a solution process or by adsorption. A contribution by adsorption was noticed on silica as well as on reversed phases based on silica with a normal phase gradient of increasing polarity (heptane to dichloromethane). Elution was solely governed by solubility of the polymers on both types of stationary phase for polystyrenes with a molecular weight above 35 000 and reversed phase gradient of decreasing polarity (methanol to dichloromethane). Under these conditions an identical dependence of elution solvent composition on sample size was found as for turbidity titrations. Due to differences in the velocity of the eluent front and the polymeric sample with porous stationary phases the polymers can be eluted as colloidal solutions Non-porous stationary phases are superior in this respect because the velocities of eluent and solutes are identical.     

Crystal hydrates: an investigation of the use of crystal hydrates as stationary phases in gas chromatography

Summary The use of crystallohydrates, crystallohydrate solutions and melts as stationary phases in gas chromatography has been proposed. Crystallohydrates have been shown to display high selectivity in the separation of polar organic compounds when use is made of water vapours as the mobile phase. Some aspects of gas-liquid chromatography in water vapours and with the stationary phase comprising crystallohydrates have been studied, and the preliminary results obtained point to the desirability of further progress in this field.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Condensed rare-earth metal-rich tellurides. Extension of layered Sc6PdTe2-type compounds to yttrium and lutetium analogues and to Y7Te2, the limiting binary member

Six isotypic R₆ZTe₂ phases have been synthesized in Ta at elevated temperatures and characterized by single crystal X-ray refinements for R=Y, Z=Rh, Pd, Ag, Y and for R=Lu, Z=Cu, Ag. All crystallize in the Sc₆PdTe₂-type structure, Pnma, Z=4, a∼21.5 Å, b∼4.1 Å, c∼11.4 Å. The results can be viewed as the replacement of Te3 atoms in the parent isotypic Sc₂Te (or in the hypothetical Y₂Te or Lu₂Te analogues) by the above the Z, the Y example giving the new binary phase Y₇Te₂. The shorter (and stronger) metal-metal bonds concentrate in the region of metal (Z, Y) substitution, as revealed by larger integrated crystal orbital Hamilton population (ICOHP) values derived from linear muffin-tin-orbital (LMTO) calculations. Partial densities-of-states data for Y₇Te₂ reflect a similar behavior. Individual R-R bond distances are seen to deviate appreciably from the more fundamental overlap population measures for each.     

Differential thermal analysis of the Al+20% (Fe-50%B) system

In the present study, aluminium and mechanically alloyed (36 h) Fe/B (50 wt%) are mixed. Al+20 (wt%) Fe/B mixture has been studied by differential thermal analysis to determine the aluminium quantity that is supposed to melt and afterwards does not solidify as it reacts with Fe/B powder. The different areas between endothermic reaction (melting peak) and exothermic reaction (solidification peak) allow in knowing the quantity of aluminium that reacts with Fe/B and the amount of intermetallic phases formed at high temperature. In order to follow the process, compacts were sintered at different temperatures (700, 800, 900, 1000 and 1200 °C), in N₂/10H₂/0.1CH₄ atmosphere. Microstructure was evaluated by image analysis and the results obtained by both techniques are compared.     

Capillary electrochromatographic separation of enantiomers under aqueous mobile phases on a covalently bonded cellulose derivative chiral stationary phase

A chemically bonded cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase (CSP) was prepared by a radical polymerization reaction. The prepared CSP was packed into fused-silica capillaries with inner diameter of 75 microm to perform enantiomer separations in CEC. The electrochromatographic behavior of the CSP was investigated. On the prepared CSP, high EOF could be generated under acidic mobile phases, which represented an advantage for the separation of acidic enantiomers. Several neutral, acidic, and basic enantiomers were resolved on the prepared CSP under aqueous mobile phases. The column efficiencies were between 20,000 and 100,000 plates/m, which were much higher than those of HPLC. In addition, it was observed that the separation of some enantiomers benefited from the adoption of THF as mobile phase modifier.     

Application of particles as pseudo-stationary phases in electrokinetic chromatography

Since the introduction of micelles by Terabe et al. (1984), many different species have been employed as carriers for electrokinetic chromatography. As it is not possible to separate uncharged solutes or ions with equal mobility in capillary electrophoresis, these phases are added to introduce or improve selectivity.

This review surveys the application of particles as pseudo-stationary phases. Up to now only very few applications exist based either on polymer particles for the separation of catechols and primary amines or silica-based material. With these particles separations are shown for phenols, polycyclic aromatic hydrocarbons and naphthalene derivatives. The characteristic properties of particles as pseudo-stationary phases and their benefits as well as their limitations are discussed.     

Selectivity of long chain stationary phases in reversed phase liquid chromatography

A series of commercial monomeric and polymeric C(18), C(27), and C(30) stationary phases were compared with immobilized poly(ethylene-co-acrylic acid) stationary phases synthesized in-house. The columns were characterized on the basis of methylene selectivity, silanol activity, metal activity, pore size, shape selectivity, and the ability to separate tocopherol isomers and carotenoid isomers. Monomeric and polymeric C(30) phases were shown to yield excellent separations of the tocopherol isomers while the polymeric C(30) and polyethylene phases were more appropriate to the separation of carotenoids.