Comparison and prediction of the retention in micellar electrokinetic chromatography and microemulsion electrokinetic chromatography for disubstituted benzenes

Retention index ( I ), rather than retention factor ( k ), was found to be a more reasonable parameter for comparison of the relative affinity of disubstituted benzenes in MEEKC and MEKC, due to independent of I with the SDS surfactant concentration. MEKC and MEEKC may give similar or different I values, depending on types of moieties. With known I and K ow for alkylbenzenes as references in MEKC and MEEKC, the values of K ow for disubstituted benzenes can be estimated from the observed I values, where K ow is the octanol–water distribution constant. In addition, a group additive approach can be used to predict I for disubstituted benzenes with different moieties from the average observed I for the disubstituted benzenes with same moieties. However, electronic effects and/or intramolecular interaction may result in the different observed I from prediction.