Factors affecting retention and resolution of hydrophobic aromatic compounds in microemulsion electrokinetic chromatography

Abstract

Retention behaviors, such as retention factor (k) and retention index (I), of homologous series compounds in microemulsion electrokinetic chromatography (MEEKC) with suppressed electroosmosis were investigated. Using alkylbenzenes (BZ) as standard, the retention indices of other homologous series compounds are independent of the concentration of sodium dodecyl sulphate ([SDS]) and temperature, while dependent on the type and concentration of organic co-solvents (phi). The retention factor increases with increasing [SDS], while decreases with increasing temperature or phi. At a given ([SDS]) and phi, excellent agreement was found between the observed and predicted values of log k of analytes in MEEKC, where the predicted values were obtained from our modified equations. Using BZ as standards, excellent agreement is found between predicted and literature values of log K[subscript ow] of the test analytes, where K[subscript ow] is the octanol-water distribution constant of the analyte. In addition, the resolution (R[subscript s]) in MEEKC and micellar electrokinetic chromatography (MEKC) was compared using bisphenol-A-diglycidlyl ether and its derivatives as test analytes. Separation scales were compared using a resolution equation, R[subscript s] = (N[superscript0.5]/4)(a-1)/(1+ k[subscript 2]), where a is the selectivity (a = k[subscript 2]/ k[subscript 1] for k[subscript 2][is more than or equal to] k[subscript 1]>0), and N the theaverage efficiency. At a given [SDS], phi and temperature, in comparison with MEKC, MEEKC was found to give better resolution of analytes, mainly due to the significantly smaller k in MEEKC, but not the greater a in MEEKC, while a comparable range of N.