Separation of very hydrophobic compounds by hydrophobic interaction electrokinetic chromatography

Separations of very hydrophobic neutral analytes were achieved using hydrophobic interaction electrokinetic chromatography (HI-EKC). Alkyl aryl ketone homologues dodecanophenone (C18), tetradecanophenone (C20), hexadecanophenone (C22) and octadecanophenone (C24) were separated via hydrophobic interactions between free sodium dodecyl sulfate (SDS) monomers and the analytes. The first running buffer consisted of 50 mM SDS and 50% acetonitrile (pH 7.0). A complete reversal in the elution order of these analytes was obtained with the second running buffer, 20 mM cetyltrimethylammonium bromide (CTAB) and 50% acetonitrile (pH 2.8). With the second running buffer, electroosmotic flow was suppressed and the free CTAB monomers migrated toward the detector. Through hydrophobic interactions between the free CTAB monomers and the analytes, separations of these very hydrophobic alkyl aryl ketones were obtained in less than 10 min; analysis times were less than 5 min with the SDS-based separations.