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 fac tors of organic analytes. An even greater reduction in k' resulted fro m 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 informing solution complexes with organ ic 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 m ore effective than any of the binary mixtures in modifying the chromat ographic behavior of organic solutes in HPLC.