Electrolytic Suppressors

The ideal way to regenerate a suppressor for IC is to electrolyze water to produce the or OH needed. Strong and Dasgupta invented a practical suppressor of this type in 1989 [5], 

In 1992 Dionex introduced a commercial electrochemical suppressor called a Self Regeneration Suppressor, or SRS [6]. The internal design is similar to the membrane suppressor, but the regenerating ion for anion chromatography) is produced by electrolysis of water. This allows the use of very low flow rates for regenerant water and avoids the use of independent chemical feed needed for earlier suppression devices. 

In this device, a platinum wire-filled tube made of a Nation cation-exchange membrane is inserted into another, larger Nation tube and coiled into a helix. The helical assembly is inserted within an outer jacket packed with granular conductive carbon. An alkaline eluent, for example, NaOH or Na2C03, flows in the annular channel between the two membranes, and pure water flows through the inner membrane and the outer jacket countercurrent to the direction of eluent flow. A DC voltage (3-8 V) is applied across the carbon bed and the platinum wire. 

Sodium ions in the eluent migrate to the cathode compartment, resulting in water as the suppressed eluent Up to 500 min of sodium hydroxide could be suppressed effectively with a membrane 50 cm in length. The band dispersion was 106 pL for a 20pL sample. 

Gjerde and Benson discovered that post-column addition of a suspension of sulfo-nated polystyrene particles may be used to reduce the background conductance of basic eluents used in anion chromatography [7]. The eluent cation (typically Na ) is also replaced in the analyte ion bands by the more highly conducting H as the 

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S. Rabian, J. Stillian, V. Barreto, K. Friedman and M. Toofan, New membrane-based electrolytic suppressor device for suppressed conductivity detection in ion chromatography, J. Chromaiogr.,... 

To remedy this problem, the solution next passes through an electrolytic suppressor, in which cations (K, in this example) are replaced by H. The net result is that... 

Figure 23 7 Electrolytic suppressor for anion chromatography replaces KOH eluent with H2O.

Figure 3.117 Cross section of an anion Atlas electrolytic suppressor.

In 2001, a third type of suppressor -Atlas Electrolytic Suppressor (AES) - was introduced. The Atlas suppressor is a continuously regenerated suppressor operated in the recycle mode and designed for optimal performance with conventional methanesulfonic acid (MSA) eluents. Able to suppress up to 25mmol/L... 

Fig. 3-79. Cross-section of an Anion Atlas Electrolytic Suppressor.

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