Comparative study of capillary zone electrophoresis and micellar electrokinetic capillary chromatography for the separation of naphthalenedisulfonate isomers

We investigated the separation of a test mixture of nine substituted and unsubstituted naphthalenedisulfonate isomers by capillary electrophoresis with a UV diode array detector. In particular, we focused on how the composition of the running buffer affected the separation selectivity. When capillary zone electrophoresis was carried out, the best results were obtained when organic solvents such as ethanol or propan-2-ol were added. Eight peaks were baseline separated but in no case were all the unsubstituted isomers separated. Therefore, capillary electrophoretic separation of the compounds was examined in the presence of micellar agents, such as sodium dodecyl sulfate, polyethylene glycol dodecyl ether (Brij 35) and cetyltrimethylammonium bromide. All the substituted isomers and two of the unsubstituted isomers were well resolved within 20 min by micellar electrokinetic capillary chromatography when Brij 35 was used as micellar agent. Separations were reproducible, in terms of peak area and migration time, under these conditions.