COMPARISON OF CHROMATOGRAPHIC BEHAVIOR OF OLIGOETHYLENE GLYCOL NONYLPHENYL ETHER NONIONIC AND ANIONIC SURFACTANTS IN REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A simple retention mechanism is proposed to describe the retention beh aviour of oligomeric sulphated and non-sulphated surfactants of the ol igoethylene glycol nonylphenyl ether type in reversed-phase systems co ntaining ion-pairing reagents in aqueous-organic mobile phases. The eq uations derived using this mechanism relate the capacity factors of th e individual oligomers to the number of oxyethylene units and to the c oncentrations of the organic solvent (2-propanol) and of the ion-pairi ng reagent (cetyltrimethylammonium bromide) in the mobile phase. Most capacity factors calculated using the best-fit parameters of these equ ations agree with the experimental values with errors of less than +/- 5% relative. The capacity factors of the anionic surfactants with vari ous degrees of polymerization on a C-18 column reach maximum values in the mobile phases containing 0.02 mol/l cetyltrimethylammonium bromid e, while the retention of the non-ionic surfactants decreases regularl y with increasing concentration of the ion-pairing reagent. The concen tration of propanol affects the retention of the anionic and non-ionic surfactants in the same way, but the anionic surfactants are more str ongly retained. The composition of the mobile phase can be optimized s o that the sulphated and non-sulphated oligoethylene glycol nonylpheny l 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.