Nanovolume Gas-Free Hydroxide Eluent Generator for Open Tubular Ion Chromatography

A gas-free KOH eluent generator (EG) with 210 nL of internal volume is described. It utilizes a two-membrane configuration where there is a single CEM layer on one side and a single BPM layer on the other side for use in open tubular ion chromatography systems with typical back pressures < 50 psi. At a flow rate of ∼190 nL/min, the 10-90% gradient rise time is 3.5 min. The device shows good linearity between applied current and concentration of KOH generated, which is stable over extended periods. The overall system reproducibility (that includes contributions from any changes in flow rate), as judged by the relative standard deviation (RSD) of the retention times of individual separated ions in repeat measurements (n = 6), ranged from <0.5% for isocratic to <1.2% for gradient elution schemes. Perceptible current flow and KOH production in the BPM-based EG begins at subelectrolytic applied voltages, prompting us to look more closely at exact field strength necessary for field-enhanced dissociation of water. An increase in the specific conductance of pure water is noticeable by a field strength of 10⁵ V/m.