Wetting transition in squalane on a silanized diatomaceous gas chromatographic support

A previously unsuspected wetting transition has been observed in a supported liquid widely used in gas chromatographic studies of solution and adsorption thermodynamics. With squalane coated on a silanized Chromosorb P support, retention volumes have been measured for acetone at 60°C, and butan-2-one and ethyl acetate at 60, 70, and 80°C. Plots of retention against liquid loading at constant solute concentration show pronounced peaks at 7.15% liquid loading. The peaks are attributed to coalescence of the liquid phase, at about 6.9% loading, from pools of low contact angle to a continous film, followed by pore-filling of the support. This finding also supports previous arguments for a major retention contribution from liquid surface adsorption when a polar solute dissolves, at low concentration, in a nonpolar liquid coated on a silanized solid surface. The implications for studies of mixed retention mechanisms, and the choice between two methods of conducting such studies, are discussed.