Gas-Free Continuously Regenerated Impurity Removal Device for Ion Chromatography

A gas-free continuously regenerated-anion impurity removal device (CR-ARD) is described for ion chromatography (IC). It is a sandwiched configuration consisting of three channels. The central eluent channel is isolated from two outer regenerant channels by stacked anion exchange membranes (sAEM) and a bipolar membrane (BPM) plus stacked cation exchange membranes (BPM-sCEM), in which the anion exchange side of BPM is facing the central channel. The sAEM side is an anode with respect to the cathode of the BPM-sCEM side. The central channel is packed with strongly basic anion exchange resins in hydroxide form. The application of an electrical voltage to the device causes enhanced water splitting at the interface of BPM to occur and the potential drives the hydroxide ions through the resin phase toward the anode, thereby enabling continuous regeneration of the resin and avoiding any off-line regeneration. Meanwhile, nonhydroxide anionic impurities (basically carbonate) are transported toward the anode through the sAEM. It does not produce gas in the eluent channel, and no degasser is required afterward. It shows a strong ability to remove anionic impurities, as indicated by effective removal of 5 mM CO₃^2- injected sample plug (25 μL, 125 pmol) or continuous removal of 600 μM KNO₃ solution at 1 mL/min (10 nmol/s) over 300 min. Much improved peak integration at the gradient mode and a higher signal-to-noise ratio at the isocratic mode can be achieved by CR-ARD. To our knowledge, this is the first account of gas-free CR-ARD.