Adsorption behaviour of zwitterionic surfactants onto a reversed-phase stationary phase

Abstract

The absorption behaviour of zwitterionic surfactants from a micellar mobile phase onto a reversed-phase octadecylsilica (ODS) stationary phase was studied. Four betaine-type zwitterionic surfactants; 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS), 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate (CHAPSO), 3-(N,N-dimethyldodecylammonio)-propane-sulfonate (C12N3S), and 3-(N,N-dimethylmyristylammonio)-propanesulfonate (C14N3S) were used as model surfactants. For all of these surfactants, similar results were observed. Breakthrough of micelles did not occur until the stationary phase had become coated at saturation with monomeric surfactant. Stationary phases prepared in this way were able to separate ions with water as mobile phase, with the separation being governed by the total amount of the surfactant passed over the stationary phase, rather than whether a micellar solution or a sub-micellar solution was used. Taken together, these data lead to the conclusion that the regardless of the type of surfactant solution in contact with the stationary phase only monomers became adsorbed until saturation of the stationary phase occurred. The amount of surfactant adsorbed onto the stationary phase at saturation was found to be 0.461, 0.480, 0.777, and 1.045 mmole column−1 for CHAPS, CHAPSO, C12N3S, and C14N3S, respectively.