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All forms of liquid chromatography use eluents that must be prepared and replenished; a widely applied form of ion chromatography (IC) also requires a suppressor and a means for regenerating it. "Ion reflux", as applied to IC, is a new ion-exchange technique where an electrically polarized ion-exchange bed becomes the source of eluent as well as its means of suppression. Using water as the pumped phase, such polarized beds enable the "perpetual" generation and suppression of eluent with little intervention by the user. In one embodiment of ion reflux, continuous eluent generation, ion separation, and continuous suppression are accomplished within a single bed. In another case, where separation is uncoupled from the other two functions, the ion reflux device may be used with existing separators. This paper describes the principles of ion reflux, the advantages and disadvantages of various embodiments, and gives examples of their use in both isocratic and gradient modes of ion separation. These new means for automating eluent generation and suppression should open pathways to new forms of IC instruments and systems.

A procedure for the sequential determination of arsenite [As(III)] and arsenate [As(V)] based on electrochemical detection for As(II1) and spectrophotometric detection for As(V) following ion chromatographic separation was developed. The color-developing system was based on the ion-association complex formed by heteropolymolybdoarsenic acid with bismuth in the presence of Triton X-100. Experimental conditions for electrochemical detection and color-developing conditions were optimized for A&II) and As(V), respectively. The optimal applied potential for electrochemical detection of As(II1) was + 0.35 V and the wavelength for spectrophotometric detection of As(V) was 700 nm. By using an eluent of 2.0 mM sodium hydrogencarbonatemM sodium carbonate with a 175 ~1 sample loop for ion chromatographic separation, the detection limits, which are defined as the concentrations that give the peak intensity twice the baseline noise, are found to be 2.9 pg/l for As(II1) and 13 pg/l for As(V), respectively. The spiked waste water samples were analyzed and recoveries were found to be 97.5-104% for As(II1) and 93.5103%for As(V), respectively.

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