Study of the Competitive Binding of TBA and CP Ions on C18Surface

Abstract

The adsorption behavior of tetrabutylammonium (TBA) and cetylpyridinium (CP) cations was studied on Hypersil 5-ODS sorbent. After establishing that CP has about 5-fold stronger affinity to the C₁₈ surface than the structurally different, symmetric, spherical molecule of TBA, the adsorption from their common solution was also examined. The data of “competitive binding” seem to show that TBA should have certain selective binding sites on the C₁₈ surface from which it can not be displaced by the CP, even in the case where the latter is present in a 4-fold excess in the mobile phase. The maximal coverage was found to be 52.9%(CP) and 12%(TBA), i.e., every second C₁₈ group is covered by CP cations and only l/8th of C₁₈ groups may interact with TBA. The accessible, proton releasing silanol content, related to the total C₁₈ content of the column, was found to be very low.