Bryon J. Tarbet

Gas chromatographic retention behavior of polycyclic aromatic compounds on smectic liquid-crystalline polysiloxane stationary phases

Abstract Factors affecting gas chromatographic retention on smectic liquid-crystalline phenyl and biphenyl carboxylate ester polysiloxane stationary phases were studied for neutral polycyclic aromatic hydrocarbons (PAHs) and slightly polar sulfur heterocycles. Retention was greatly affected by the molecular geometry of the solutes in addition to other contributions such as solute vapor pressure and polarity. The major geometrical factor was the length-to-breadth ( L/B ) ratio of the solutes, while of less importance, but still significant, was the solute molecular shape. The effect of solute ( L/B ) on selectivity was larger in the smectic region than in the nematic region. Furthermore, the selectivity of the smectic phase was generally better than that of the nematic phase. Compounds with at least four aromatic rings annelated in a straight line were retained much longer, and compounds with aromatic rings annelated in a curved or arc-like arrangement were retained much less, than predicted by the ( L/B ) ratios for these compounds. Arc-like molecules with groups attached to the outer curved side were, however, retained longer than predicted. Lower chromatographic efficiencies were measured for the arc-like molecules as compared to the latter type of molecules. The latter appear to penetrate the laminar arrangement of the polymer liquid-crystalline side groups more easily, thus leading to better solute diffusion and improved mass transfer.

Complexing and Chelating Agents Immobilized on Silica Gel and Related Materials and Their Application for Sorption of Inorganic Species

Abstract Solid materials bearing bonded organic functional groups are reviewed. The properties of the oxide supporting materials, silica gel in particular, their chemical and physical properties and the nature of the surface residues are part of this review. Processes leading to modification of the silica gel surface with mono- and polylayers of other oxides resulting in materials with modified properties as well as their susceptibility to chemical modification are also presented. Data on silanization procedures to bond supporting materials with commercial or synthesized organosilicon compounds have been carefully collected and discussed. Special emphasis has been paid to reactions which change the chemical nature of the bonded organic residues leading to valuable materials for partition, ion, ion-exchange, and affinity chromatography as well as for specific separation methods. Data on the collection, separation and preconcentration of inorganic species using these materials are an important part of this ...

Polarizable polysiloxane stationary phases for capillary column gas chromatography

Abstract Polysiloxane polymers, containing polarizable biphenyl, naphtyl and phenoxyphenyl side groups, were synthesized and evaluated for capillary column gas chromatography. Although the more polar cyanopropyl stationary phase demonstrated better resolution of components in a wide-polarity-range mixture, the polarizable phases demonstrated better resolution of polar isomers. The “softer” dipole—induced dipole interaction between the solute and stationary phase, as compared to the dipole—dipole interaction with a polar stationary phase, is more sensitive to slight molecular differences in isomeric structures. The biphenyl polysiloxane, on the whole, demonstrated the best selectivity in a number of isomer separations.

Polysiloxanes containing thermally stable chiral amide side-chains for capillary gas and supercritical fluid chromatography

Abstract Six new polysiloxane materials containing chiral amide side-chains have been prepared by the hydrosilylation of appropriate amide-containing alkenes onto polyhydromethylsiloxane. The alkenes were prepared from either 4-allyloxybenzoic acid or 4-vinylbenzoic acid and the following chiral amines: (S) -1-(1 -naphthyl)ethylamine, (R) -α-methylbenzylamine, the 4-methoxyphenyl ester of alanine and the isopropyl ester of isoleucine. The polysiloxane containing about 7% of the chiral amide prepared from (R) - N -(α-methylbenzyl)-4-allyloxybenzamide proved to be an efficient stationary phase for the capillary gas chromatographic separation of the enantiomers of the N -pentafluoropropionyl isopropyl esters of amino acids of which one example is given. This stationary phase was stable to 280°C.

Selective Gas Chromatographic Stationary Phases for Nitrogen-Containing Polycyclic Aromatic Compounds

Abstract Several selective polysiloxane stationary phases were evaluated for the resolution of nitrogen-containing polycyclic aromatic compounds (N-PAC) in coal tar fractions by capillary column gas chromatography. A new liquid crystalline polysiloxane exhibited the highest selectivity for isomeric alkylated 3- and 4-ring N-PAC, whereas a polarizable biphenyl polysiloxane and a moderately polar crown ether-substituted polysiloxane were more applicable for the analysis of 2- and 3-ring N-PAC. The thermal stabilities of these phases made them suitable for GC-MS applications.

Stable Silica Gel-Bound Crown Ethers. Selective Separation of Metal Ions and a Potential for Separations of Amine Enantiomers*

Silica gel-bound crown ethers and aza macrocycles have been synthesized with the attaching arm connected to the carbon framework of the macrocycles. The interactions of these bound macrocycles with cations are almost identical to those involving the analogous free macrocycles. This has allowed for predictable cation separation, concentration, and removal processes to be performed on a small scale. Quantum mechanical calculations and NMR measurements indicate that similarly bound chiral macrocycles will be capable of use in separating chiral organic amines.

Preparation of silica gel-bound macrocycles and their cation-binding properties

Values of log K for the association of several metal cations with 15-crown-5, 18-crown-6, and N,N′-dibenzyldiaza-18-crown-6, each covalently bonded to silica gel, were found to be nearly the same as those for the association of the same cations with the unbound macrocycles; this observation indicates the possibility of building pre-determined cation selectivity into these permanent macrocycle-bound silica gel systems.

NEW NITROGEN-CONTAINING MACROCYCLIC LIGANDS COVALENTLY ATTACHED TO SILICA GEL AND THEIR USE IN SEPARATING METAL CATIONS

ABSTRACT Several polyaza-crowns and cyclams, each containing an allyl-oxymethyl or other monofunctional group capable of further reaction to attach it to silica gel, have been prepared. As an example of an attachment of a crown to silica gel, allyloxymethyl-substituted diaza-18-crown-6 was reacted with triethoxysilane to form the crown-substituted triethoxysilane This crown-silane material was heated on silica gel to effect a covalent attachment of the crown. The silica gel-bound macrocyclic ligands were found to interact with various metal cations with log K ( H2O) values similar to those of the same cations with unbound macrocycles. A tetraaza-crown bound to silica gel was found to quantitatively remove toxic heavy metal ions, such as Pb2+, Hg2+ Cd2+ Ag+and others at the ppb level, from large volumes of aqueous solutions containing those metal ions and much larger amounts of Na+Mg2+and Ca2+ions

Synthesis and structural considerations of oligoethylene oxide-containing polysiloxane stationary phases in capillary gas and supercritical-fluid chromatography

Abstract A series of oligoethylene oxide-containing polysiloxanes were prepared by hydrosilylating the appropriate oligoethylene oxide-containing alkene onto a well-defined polymethylhydrosiloxane polymer. The most convenient oligoethylene oxide-containing alkenes were prepared from eugenol and the tosylate of di- or triethylene glycol monomethyl ether. The polysiloxane phase prepared from 1-(4-allyl-2-methoxyphenoxy)-5-methoxy-3-oxapentane was found to possess desirable chromatographic properties when used in capillary supercritical-fluid chromatography and is suggested as a substitute for Carbowax 20 M . The phase was usable at temperatures from 20°C to 300°C. The synthetic rationale and the effects of structural changes in the polymers on chromatographic performance are discussed in this paper. This paper also contains a systematic study of the influence of chemical structure on chromatographic properties of the resulting polysiloxane phases.

Computational prediction of trends in the selectivity of macrocyclic receptors for anions

We seek a theoretical method which is capable of predicting trends in the binding affinity of macrocyclic receptors for various anions in aqueous solution. Success has been achieved in this endeavor by employing semiempirical methodology to compute the energetics of certain exchange reactions whereby anions are exchanged between a macrocyclic receptor and a cluster of water molecules. The method is computationally tractable with workstation-class computing hardware and is applicable to a wide range of guest/host systems. Computations for several anion/receptor systems are reported.