Extending the concentration limit of electrodialytic eluent generator for ion chromatography

Electrodialytic eluent generators (EEGs) are established devices for producing high-purity base or acid eluents for ion chromatography (IC). Most commercial EEGs recommend a maximum output concentration of 100 μeq/min. Here we investigate the concentration limits and key constraints. To this end, single-membrane (SM) and dual-membrane (DM) EEGs (6.2 cm² membrane area) were fabricated. The SM-EEG achieved ∼180 μeq/min at 16 MPa backpressure and ∼300 μeq/min without backpressure, with the difference attributed to accumulated gas bubbles in the eluent. A degasser limited useable output to 100 μeq/min in suppressed IC, and higher concentrations required reduced flow rates (e.g., 160 mM at 0.05 mL/min). The DM-EEG reached ∼510 μeq/min without backpressure and ∼300 μeq/min at 16 MPa, with gas-free eluent enabling broader operation. Further increases are limited by membrane current density and gas accumulation in donor chambers. Nevertheless, the concentration range of DM-EEG under typical IC backpressure can be readily doubled (up to ∼600 μeq/min) through simple tandem DM cartridges, which adequately meets the demand for high-concentration eluents in sugar analysis (e.g., 480 mM KOH).