Retention factor and retention index of homologous series compounds in microemulsion electrokinetic chromatography employing suppressed electroosmosis

The retention factor ( k ) and retention index ( I ) of homologous series compounds such as alkylbenzenes (BZ), alkylaryl ketones, alkylbenzoates, and alkylparabens in microemulsion electrokinetic chromatography (MEEKC) with suppressed electroosmosis were investigated in a wide range of SDS concentrations ([SDS]), temperatures, and concentrations of organic cosolvents ( φ ). Using BZ as standards, the retention indices of other homologous series compounds were determined and they were found to be independent of [SDS] and temperature, while are dependent on the types and concentrations of organic cosolvents. The retention factor linearly increases with increasing [SDS], while linearly decreases with increasing temperature. The value of log k linearly decreases with increasing φ for methanol, ethanol, or ACN, while decreases by a second‐degree polynomial with increasing φ for 2‐propanol. Excellent agreement was found between the observed and predicted values of log k of analytes in MEEKC at given [SDS] and φ , where the predicted values were obtained from modified equations of the linear relationship of log k as functions of [SDS], the number of carbons, and φ . Therefore, both k and I can be used for peak identification of homologous series compounds.