Comparison of chromatographic behaviour of oligoethylene glycol nonylphenyl ether non-ionic and anionic surfactants in reversed-phase high-performance liquid chromatography

Abstract

A simple retention mechanism is proposed to describe the retention behaviour of oligomeric sulphated and non-sulphated surfactants of the oligoethylene glycol nonylphenyl ether type in reversed-phase systems containing ion-pairing reagents in aqueous-organic mobile phases. The equations derived using this mechanism relate the capacity factors of the individual oligomers to the number of oxyethylene units and to the concentrations of the organic solvent (2-propanol) and of the ion-pairing reagent (cetyltrimethylammonium bromide) in the mobile phase. Most capacity factors calculated using the best-fit parameters of these equations agree with the experimental values with errors of less than ± 5% relative. The capacity factors of the anionic surfactants with various degrees of polymerization on a C 18 column reach maximum values in the mobile phases containing 0.02 mol/l cetyltrimethylammonium bromide, while the retention of the non-ionic surfactants decreases regularly with increasing concentration of the ion-pairing reagent. The concentration of propanol affects the retention of the anionic and non-ionic surfactants in the same way, but the anionic surfactants are more strongly retained. The composition of the mobile phase can be optimized so that the sulphated and non-sulphated oligoethylene glycol nonylphenyl ethers are distinguished into two groups of peaks and the separation of the individual oligomers in the two groups is possible in a single run.