Brian A. Jones

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.

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.

Nonextractable cyanopropyl polysiloxane stationary phases for capillary chromatography

SummaryCrosslinkable cyanopropylpolysiloxane stationary phases have been difficult to produce because of steric effects of the large cyanopropyl groups or because of the interaction between the polar cyanopropyl groups and the groups added for crosslinking. Various polymers containing 50% to 90% cyanopropyl were synthesized which contained vinyl,p-tolyl, or 4-vinylphenyl groups for crosslinking. Thep-tolyl group was found to give satisfactory crosslinking if there were two such groups attached to one silicon atom.

Characterization and evaluation of cyanopropyl polysiloxane stationary phases for gas chromatography

Abstract The compositions of commercial cyano-containing polysiloxane stationary phases were determined using infrared, nuclear magnetic resonance, and proton-induced X-ray emission spectroscopies. Varying amounts of the polar carboxamide group were found in most polymers. This group, which is inadvertently formed during the hydrolysis step in the synthesis of the polymers, affects the polarity and selectivity of the phase. The chloride ion (believed to be present as HCl as a result of the synthesis from dichlorosilane monomers) was also detected. A specially synthesized 88% cyanopropyl polysiloxane from dimethoxysilane monomers, containing no detectable carboxamide groups or adsorbed HCl, possessed different properties than the comparable commercially available phases.

σ retrieval from SeaWinds on QuikScat

NASA has developed a new scatterometer, SeaWinds, which is scheduled to be launched on two missions, one in 1999 and the other in 2000. SeaWinds will measure the speed and direction of near-surface winds over the ocean. A fundamental part of the processing of SeaWinds data is the computation of (sigma) degree which includes solving the radar equation for every pulse sent and received by the scatterometer. However, for SeaWinds, this calculation is too computationally intensive to perform in real tie. Instead, a method of tabularizing most of the calculation has been developed. This method includes corrections for attitude and orbit perturbations and accounts for the elevation of the local topography. It also includes a table which will be used to assist ground data processing in determining the locations of the measurements. Tests comparing the tabulated result with the actual numerical calculations have shown that using this table is accurate to within +/- 0.1 dB and gives locations that are accurate to within 160 meters. We provide a description of this algorithm. The innovations developed as part of this algorithm may be of interest in processing data from other remote sensing systems.