Coupling of a gas-phase chemiluminescence nitrogen detector and a capillary electrophoretic system

A capillary electrophoretic system has been successfully connected to a gas -phase chemiluminescence nitrogen detector via a pneumatic nebulizer interf ace. The interface, built in-house, consists of a nebulizing gas delivery s ubsystem, a sheath liquid subsystem, a short spray tube, and a liquid gap. The liquid gap is formed at the point where the spray tube, the separation capillary, and the sheath liquid subsystem meet. The sheath liquid subsyste m consists of a grounding connection to complete the electric circuit for t he electrophoretic system, a sheath liquid delivery pump, a sheath Liquid o verflow outlet maintained at atmospheric pressure, and a sheath liquid cond uit with a hydrodynamic resistance that is much smaller than that of the se paration capillary. The interface operates at the natural self-aspiration r ate of the short spray tube. The design ensures that the natural self-aspir ation rate of the nebulizer is higher than the maximum electroosmotic now r ate that can be produced in the separation capillary. The now difference is made up by the sheath liquid which, due to the hydrodynamic resistance dif ferences, is sucked into the liquid gap preferentially from the sheath liqu id conduit. Thus, the spray tube and the separation capillary are decoupled from each other hydrodynamically, and any laminar now-induced additional b and broadening in the separation capillary is avoided, Using the combined e lectrophoretic separation and gas-phase chemiluminescence nitrogen detector system, the mass detection limit for five nucleotide bases used as test co mpounds was found to be about 10 pmol nitrogen.