Journal of Chromatography A, 1216 (2009) 2412–2416 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma A multifunctional dual membrane electrodialytic eluent generator for capillary ion chromatography Bingcheng Yang a,∗ , Feifang Zhang a,c , Xinmiao Liang a,c , Purnendu K. Dasgupta b a School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China b Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019-0065, USA c Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China article info Article history: Received 10 November 2008 Received in revised form 27 December 2008 Accepted 9 January 2009 Available online 15 January 2009 Keywords: Electrodialytic eluent generator Capillary ion chromatography Dual ion exchanger abstract A multifunctional electrodialytic generator (EDG) for capillary ion chromatography (CIC) is described. The same device can generate acidic, basic or saline eluents. Two oppositely charged ion exchange beads are used to fabricate the EDG; the dual ion exchanger configuration ensures the production of gas-free eluent, obviating the need of a gas removal device used with single ion exchanger EDG’s. The ability of the same EDG to produce different eluents is governed solely by the choice of the respective feed solutions; this is presently demonstrated by generation of diverse eluents such as Na 2 CO 3 /NaHCO 3 , CH 3 SO 3 H, and KNO 3 . The EDG is implemented simply in a commercial cross fitting and has been tested up pressures to 2000 psi. Under typical operating conditions, the zero current concentration (open circuit penetration, OCP) is negligible. The generated eluent concentration linearly increases with applied current with a slope that is essentially Faradaic. The device permits both isocratic and gradient operation with good reproducibility, as demonstrated by the analysis of anions using HCO 3 - /CO 3 2- EDG. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The introduction of the electrodialytic generator (EDG) for elu- ents [1–5] has been a milestone in ion chromatography (IC). In IC, acids and bases (or salts of weak acids) are commonly used as chromatographic eluents; neutral salts have been used in chro- matographic determination of the hydronium ion [6] and can be useful in chromatographic separation of transition metal ions as well [7]. Until the advent of the EDG, eluent preparation was strictly manual. With the exception of the preparation of weak acid salt eluents like carbonate/bicarbonate for which commercial offerings, that actually uses two separate devices, are available [8], the prepa- ration of neutral salt or simple buffer based eluents is still manual. This is tedious, contamination-prone and subject to operator errors. Preparing hydroxide eluents commonly used for suppressed anion chromatography is especially problematic, as they are easily con- taminated by atmospheric CO 2 . An online EDG not only eliminates the above problems, it renders gradient elution a simple matter of current programming the EDG, rather than mechanical blending of solutions. Over the past several years, EDG-equipped IC systems have gained much popularity. Configurationally, EDGs may be classified as containing (a) a single-membrane (this includes stacks of similar membranes that ∗ Corresponding author. E-mail address: bcyang06@hotmail.com (B. Yang). functions as a single thick membrane for compatibility with high pressure), (b) two similar membranes (e.g., both cation exchang- ers) with the eluent production channel therebetween, and (c) two oppositely functionalized membranes (one cation exchanger, one anion exchanger). The overwhelming majority of extant eluent EDGs, including commercial versions, fall in the single-membrane class. They do have the disadvantage of the product being accompa- nied by copious amounts of gas, H 2 (for a generated base eluent) or O 2 (for a generated acid eluent) that must be removed before enter- ing the chromatographic system. The second configuration has only been explored on a limited basis [1,2]. The design is inherently current-inefficient, for example for a base generator the membrane on the cathodic side must offer much greater resistance to mass transfer than the feed membrane. While this is possible to accom- plish by creating a barrier to mass transfer on the exit side, not only is Faradaic efficiency low, Joule heating and other factors limit the maximum eluent concentrations that can be generated. Configura- tions (b) and (c) can both generate gas-free eluent but it is possible to do so in (c) in a current efficient manner. Obviating the need of a gas-removal device greatly reduces the mixing volume, of benefit to gradient operations, especially in a capillary ion chromatography (CIC) system. The first EDG systems for IC [1–3] operated on the low-pressure side. The first EDG that operated on the high-pressure side of the pump was a capillary-scale NaOH EDG [5]. Small et al. [9] subse- quently reported the use of electrically polarized ion-exchange beds for electrically governed eluent generation. Such packed-column 0021-9673/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2009.01.025