Mixed-mode capillary electrokinetic separation of positional explosive isomers using sodium dodecyl sulfate and negative-β-cyclodextrin derivatives

A mixed-mode capillary electrophoretic technique has been developed for the separation of positional nitroaromatic explosive isomers. The procedure utilized two different buffer additives as pseudo-stationary phases with different selectivities towards the analytes. Sodium dodecyl sulfate (SDS) displayed selectivities for the explosives which were similar to C₁₈ reversed-phase HPLC. The negatively charged sulfobutyl ether-β-cyclodextrin (SB-β-CD), sulfated-β-CD and succinylated-β-CD separated the explosives on the formation of inclusion complexes with the analytes, and exhibited different selectivities for the explosives compared to SDS. A mixed pseudo- stationary phase was then formulated by combining 10 mM SB-β-CD, 30 mM SDS and 10% acetonitrile in 20 mM borate at pH 9 to resolve the two most difficultly separated pairs: 1,3-dinitrobenzene/1,4-dinitrobenzene and 3- nitrobenzene/4-nitrobenzene.