Mixed Surfactants as Mobile Phase Additives for the Separations of Organic Compounds by HPLC

A low concentration of a surfactant added to a mobile phase containing 60% acetonitrile (+ 40% water) significantly reduces the capacity factors of organic analytes. An even greater reduction in k‘ resulted from the use of binary additive systems, particularly those containing a cationic and an anionic surfactant. It is believed that an ion pair is formed that is more effective in forming solution complexes with organic analytes than either additive alone. Other binary additive systems included mixtures of a neutral and a charged additive or a mixture of two anionic surfactant additives. A ternary mixture of additives was more effective than any of the binary mixtures in modifying the chromatographic behavior of organic solutes in HPLC.