Electrically Polarized Ion-Exchange Beds in Ion Chromatography:  Ion Reflux

Abstract

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.

Autonomous, waste-free eluent generation and suppression in a single device: Electrodialytic eluent reflux for ion chromatography

“…In electrodialysis, ions from electrolysis are transported across the membranes when a potential is applied. Various electrodialytic devices and their conductive properties have been presented in previous works [5,[13][14][15][16][17]. In particular, Small [5] has reported on the use of packed ion exchange resin beds as eluent generators, and Yang [18] has shown how the addition of membranes into an electrolytic device can provide a gas-free, efficient method of eluent generation.…”

“…Samples also underwent pre-treatment to avoid the loss of suppressor capacity [13]. Before the injector, samples were pumped through a cation exchange bed in the hydronium form.…”

“…In research conducted by Small [13] a technique termed ion reflux was described. Ion reflux completely eliminated the problem waste generation through the use of an electrolytic device.…”

“…There, potassium ions from the cation ion exchange resin combine with incoming hydroxide from the cathode, forming potassium hydroxide. Hydronium ions from the anode electromigrate toward the cathode and eventually meet potassium hydroxide, establishing a potassium-hydronium boundary [5,13]. The continuous production of hydronium from the anode keeps the potassium from leaving the resin bed, and thus the potassium is conserved or refluxed, eliminating waste.…”

“…An additional advantage to ion reflux is that a single resin bed can act as the eluent generator, separator and suppressor using only water as the pumped phase [13]. However, as was seen in eluent regeneration, the original implementation of ion reflux also resulted in the exposure of eluent to electrolysis gases and electrochemical byproducts.…”