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The three 75% phenyl, 25% methyl‐polysiloxanes OV‐25, PS162, and a new laboratory‐made polymer called SOP‐75 were coated on fused silica capillary columns and tested in high temperature gas chromatography. The synthesis of SOP‐75 as a methoxy‐terminated, symmetrically substituted 75% diphenyl, 25% dimethyl‐polysiloxane is reported. For better comparison the polymers were characterized by 1H and 29Si nuclear magnetic resonance spectroscopy. The coated fused silica capillary columns were evaluated in respect of their selectivity, inertness, separation efficiency, and bleeding. The three stationary phases exhibited similar selectivity and high inertness up to 400 or 410°C. A minimum allowable operating temperature was established, since the capillaries offered insufficient separation efficiency at low temperatures. SOP‐75 offered the best chromatographic properties with superior separation efficiency compared to PS126 and OV‐25. A commercially available capillary column with similar polarity was used for comparison, where increased separation efficiency and inertness but also increased bleeding of SOP‐75 were found. Improved separation of triacylglycerol mixtures was obtained due to the increased polarity and thermal stability of SOP‐75. So far, SOP‐75 is the polysiloxane with the highest phenyl content that has been successfully coated onto fused silica capillary columns for high temperature gas chromatography.

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An n-octylmethyl, diphenyl-polysiloxane called SOP-50-Octyl was prepared by a condensation reaction of bis(dimethylamino) n-octylmethylsilane with diphenylsilanediol. The resulting copolymer was a gum with high molecular weight and was obtained with a yield of 80%. 1H and 29Si NMR spectroscopy revealed that the copolymer was a 52% octylmethyl, 48% diphenyl-polysiloxane with random microstructure. Small cyclic impurities could be almost quantitatively removed via a purification step. SOP-50-Octyl was used as stationary phase for the preparation of wall coated open tubular fused silica capillary columns for gas-liquid chromatography. The capillary columns exhibited high separation efficiency and high inertness. The stationary phase offered a unique selectivity due to its unique composition. The Rohrschneider-McReynolds constants indicated a low overall polarity in spite of the high phenyl content, as the polarity was distinctly decreased by the octyl substituent. Furthermore, the octyl substituent was responsible for a high column bleed, reducing the maximum allowable operating temperature to 280 degrees C. The elution temperatures of apolar compounds were increased due to increased interaction of the octyl substituent with the analytes. Some applications with volatile and semi-volatile organic compounds illustrate that SOP-50-Octyl is an excellent choice for confirmational analyses.