The most versatile columns for this type of separation are the Cogent TYPE-C Silica™ columns because the amount of retention in both modes can be adjusted by the type of modification and the mobile phase composition. Polar endcapped and polar embedded columns have this same capability since they are also classified as mixed-mode stationary phases. The degree of polar retention depends on the endcapping group or the embedded group.
With Cogent TYPE-C Silica columns, we have observed not just RP and ANP mechanisms operating, but also hydrophobic compounds retained by an ANP mechanism. In this latter case, certain functional groups such as amines or carboxylic acids are thought to play a significant role in ANP retention even if the compound is very hydrophobic.