Capillary Ion Chromatography with On-Line High-Pressure Electrodialytic NaOH Eluent Production and Gradient Generation

A small inexpensive system is described that allows high-performance suppressed anion chromatography on a capillary scale. A fully computer-controlled stepper motor-driven syringe-type dispenser, equipped with a 500 μL-capacity glass syringe is capable of pumping at pressures up to 1000 psi when equipped with an appropriate inlet check valve. Fused-silica capillary columns ∼50 cm in length and 180 μm i.d., packed in-house with a commercial packing, provide excellent performance, significantly exceeding the efficiencies observed for the same packing in commercially available 2 mm bore format. The system operates with a pressure drop of <800 psi at a flow rate of 2 μL/min. The system utilizes a novel electrodialytic NaOH eluent generator that is deployed on the high-pressure side of the pump and thus requires no special measures for electrolytic gas removal. This device permits both isocratic and gradient operation with excellent eluent purity; the NaOH concentration is generated linearly with applied current with near-Faradaic efficiency, up to a concentration of at least 100 mM.