A 50% n-octylmethyl, 50% diphenyl-polysiloxane as stationary phase with unique selectivity for gas chromatography

Nitro- and fluoro-substituted tetraphenyl–phenyl grafted polysiloxanes as stationary phase for capillary gas chromatography

This work reports the synthesis of 2,5-di(4-nitrophenyl)-3,4-di(3,5-difluorophenyl)phenyl grafted polysiloxane (NDPP; containing 12.4% 2,5-di(4-nitrophenyl)-3,4-di(3,5-difluorophenyl)phenyl groups) for gas-chromatography (GC) separation.

Polysiloxanes-based stationary phases containing methoxy-substituted tetraphenyl–phenyl groups for gas chromotographic separations

3,4-Di(4-methoxy phenyl)-2,5-diphenyl phenyl grafted polysiloxane (MTP) and 3,4-di(3,4,5-trimethoxy phenyl)-2,5-diphenyl phenyl grafted polysiloxane (TMP) were synthesized and statically coated on fused silica capillary columns.

Determination of the minimum allowable operating temperature of stationary phases in capillary columns by inverse gas chromatography

A method was developed to determine the minimum allowable operating temperature (MiAOT) of wall coated open tubular capillary columns. Two polyethylene glycol and fourteen polysiloxanes phases with different side groups (methyl, phenyl, cyanopropyl, trifluoropropyl, n-octyl) and backbone stiffening units (tetramethyl-p-silphenylene, tetramethyl-p,p'-sildiphenylene ether, carborane) were investigated by inverse gas chromatography. A sigmoidal profile of temperature versus column efficiency was found for almost all phases, as the column efficiency increased with temperature. The MiAOT was defined as that temperature where the column efficiency is half of its original value at elevated temperatures. It was found that the MiAOT of a stationary phase is approx. 60 K higher than its glass transition temperature.

Tetramethyl-p,p′-sildiphenylene ether–dimethyl, diphenylsiloxane copolymers as stationary phases in gas chromatography

A 33% tetramethyl-p,p'-sildiphenylene ether (SDPE)-67% dimethylsiloxane copolymer was prepared and characterized by 1H and 29Si NMR spectroscopy. The random copolymer was coated on fused-silica capillary columns and used as stationary phase in GC. Highly deactivated capillary columns with high separation efficiency and a working range from -10 to 400 degrees C were obtained. For comparison, a commercially available capillary column with an SDPE-diphenyl, dimethylsiloxane terpolymer was tested. The selectivity of SDPE phases is best described by the assumption that an SDPE unit is equivalent to two dimethylsiloxy and one diphenylsiloxy group. Both capillary columns exhibited low column bleed in combination with seriously increased elution temperatures.

Approaches for the coating of capillary columns with highly phenylated stationary phases for high-temperature GC

Two highly phenylated tetramethyl-p-silphenylene-diphenylsiloxane copolymers were coated on fused silica capillary columns and used as stationary phases in GC. The copolymers offered new insights into the coating process and column preparation due to their physicochemical properties. The fused silica capillary surface had to be pretreated in various ways to achieve a homogeneous film and a well deactivated surface: etching with ammonium bifluoride; leaching with sodium hydroxide and hydrochloric acid; silylation with tetraphenyldimethyldisilazane and triphenylsilylamine. Droplet formation was observed on tetraphenyldimethyldisilazane silylated surfaces leading to capillary columns with low separation efficiency. The topology of inhomogeneous films was investigated by light microscopy, scanning electron microscopy, and Auger electron spectroscopy. It became apparent that the stationary phase did not form droplets but islands, which are connected by a wetting layer according to the Stranski-Krastanov growth mode. Both copolymers are potential stationary phases for high-temperature GC with promising properties. They offer a higher overall polarity than 75% phenyl, 25% methyl-polysiloxanes in combination with increased thermal stability and reduced bleed levels.