CRITICAL COMPARISON OF GAS HEXADECANE PARTITION-COEFFICIENTS AS MEASURED WITH PACKED AND OPEN-TUBULAR CAPILLARY COLUMNS

The use of gas chromatography to study the thermodynamics of solute-so lvent interactions is very well established. Many successful measureme nts using non-polar solutes have been reported. However, the investiga tion of the properties of even moderately polar solutes, such as aceto ne, on porous particles in packed beds is fraught with potential chemi cal problems including interfacial adsorption at the solid-gas and liq uid-solid interfaces. In order to minimize, but likely not eliminate s uch effects, we have employed fused-silica open tubular capillary colu mns. This approach affords, relative to other supports, a very inert s olid surface with low net area for both the solid-gas and liquid-solid interfaces. Due to the very small amount of stationary phase liquid, it is not possible to measure the absolute value of the partition coef ficient. However, it is possible to obtain precise measurements of rel ative partition coefficients. Using the absolute value of the partitio n coefficient for some reference solute, obtained by alternative metho ds, absolute values can be computed. In this work, we show that solute retention on n-hexadecane is independent of solute concentration over a usefully wide range in the amount of solute injected. Where the cap acity factors do vary with the amount injected, they do so in a direct ion consistent with a partition dominated process. Values for the part ition coefficients for 105 non-polar and polar solutes in n-hexadecane are reported and critically compared to literature values.