Influence of composition and temperature on the selectivity of stationary phases containing either mixtures of poly(ethylene glycol) and poly(dimethylsiloxane) or copolymers of cyanopropylphenylsiloxane and dimethylsiloxane for open-tubular column gas chromatography

The solvation parameter model is used to determine the system constants for three columns containing mixtures of poly(dimethylsiloxane) and poly(ethylene glycol) and a poly(cyanopropylphenyldimethylsiloxane) containing 6% of cyanopropylphenylsiloxane monomer at five equally spaced temperatures in the range 60-140°C. Together with literature data for a poly(dimethylsiloxane) and a poly(ethylene glycol) stationary phase the influence of temperature and composition on selectivity is studied for mixing ratios of 0 to 1 poly(ethylene glycol) for the temperature range 60-140°C. Using literature data for two poly(cyanopropylphenyldimethylsiloxane) stationary phases containing 14% and 50% of cyanopropylphenylsiloxane monomer groups the influence of temperature and replacing dimethylsiloxane monomer groups by cyanopropylphenylsiloxane groups on selectivity is studied for incorporation of 0 to 0.5 cyanopropylphenylsiloxane groups over the temperature range 60-140°C. Addition of poly(ethylene glycol) or introduction of cyanopropylphenylsiloxane monomer groups into a poly(dimethylsiloxane) influences selectivity through an increase in dipolarity/ polarizability, hydrogen-bond basicity, electron lone pair interactions, and changes in cohesion. The changes in system constants as a function of temperature and composition are simply modeled as smooth quadratic response surfaces. Curvature in the response surfaces along the composition axis is significant while changes along the temperature axis are modest for both stationary phase types. Cluster analysis is used to demonstrate that the mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phases containing 0.5 and 0.85 weight fraction of poly(ethylene glycol) have different selectivity to a database of common open-tubular column stationary phases. The mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phase containing 0.10 weight fraction of poly(ethylene glycol) has similar selectivity to the poly(cyano-propylphenyldimethylsiloxane) containing 6% cyanopropylphenyl monomer groups, and could replace the mixed phase for all but the most critical of separations.