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 CO32- 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.

An integrated dual-functional electrodialytic membrane suppressor for ion chromatography.

An integrated dual-functional electrodialytic membrane suppressor (D-EMS) is proposed that can simultaneously conduct suppression of acid and base eluent. It consists of four chambers, equivalent to half an anion electrolytic membrane suppressor (EMS) plus half a cation EMS with typical sandwiched configuration via a bipolar membrane (BPM). Anion exchange membrane, BPM and cation exchange membrane are respectively used to isolate two central eluent channels from two outer regenerant chambers. A constant current source is used to power d-EMS. The device shows similar performance to a separate EMS in terms of suppression capacity (≥80 µeq/min, corresponding to 80 mM eluent at the flow rate of 1 mL/min) and the resultant suppressed background (∼0.75 µS/cm and ∼0.17 µS/cm for anion and cation section of d-EMS, respectively).

A reagent-free acid-base titration method via an electrodialytic titrant generator.

We describe a reagent-free acid-base titration method, in which only water is added and the titrant is online electrodialytically produced. Electrodialytic eluent generator, a well-established technique in ion chromatography to produce high purity base or acid eluent through precise control of an electric current, has been for the first time used for titration, termed as electrodialytic titrant generator (ETG). Three kinds of titrants produced by ETG have been demonstrated, including potassium hydroxide, methanesulfuric acid and sulfuric acid. A series of titrants with different concentration up to at least 140 mM (e.g. KOH) could be accurately and reproducibly obtained by manipulating current and the KOH titrant showed extremely high purity. The titration results achieved by ETG were in a good agreement with those obtained by the regular way and their ratio was in the range of 0.9918 and 1.0034. Good accuracy and precision were achieved for ETG titration, as indicated by 2.2% of relative error and 0.17% of relative standard error. Its utility was demonstrated to measure pKa-differentiated capacity of anion exchange resins.