Gas chromatography of polar solutes in electron acceptor stationary phases

Abstract

Two useful electron acceptor stationary phases have been developed which give a different pattern of solute retention behaviour from that found in electron donor type phases. These are the di-wH-octafluoropentyl ester of tetranitrodiphenic acid and tetrameric bis(l,l,9-trihydrohexadecafluorononyl) phosphonitrilate. They were chosen as a result of a study of the retention behaviour of solutes of various types in a number of new stationary phases. The initial specific retention volumes and Kovats indices of a number of solutes from ten homologous series were determined at 100� and 150� in these acceptor phases, in the non-polar phase Apiezon L and in the electron donor poly(ethyleneglycol succinate) for comparison. The two acceptor phases studied show large differences in solute retention behaviour from the non-polar and from the donor-type polar phase. The former have been shown to be suitable for solute identification, the analysis of perfluoro compounds, and useful in the study of electron donor-acceptor interactions by gas chromatography. From the specific retention volumes of these solutes the contributions to the changes in free energy, heat, and entropy, due to various functional groups, were determined for the process of transfer of the solutes from dilute vapour to solution in the liquid solvent. It was found that the retention of polar solutes in the polar solvents was dependent on both dipole interaction and specific donor-acceptor interaction between solute and solvent. The retention behaviour of two homologous series of perfluoro alcohols in poly(ethyleneglycol succinate) was found to be anomalous; the higher members of the series had lower retention volumes than the lower members. This was shown to be due to the combination of very weak interactions of the lyophobic perfluoroalkyl groups with the solvent molecules and the relatively strong interactions between the solvent molecules themselves.