Electrolytic Eluent Generation: The “Just Add Water” Approach to Ion Chromatography

Dilute solutions of salts, acids and bases are commonly used as eluents in ion chromatography. Traditionally, these eluents are prepared off-line by dilution with reagent-grade chemicals. Off-line preparation of these eluents can be tedious, prone to operator errors, and often introduce contaminants. For example, diluted sodium hydroxide (NaOH) solutions, widely used as eluents in the IC separation of anions, are easily contaminated by carbonate. Preparing carbonate-free NaOH eluents is difficult because carbonate can be introduced as an impurity from the reagents or by adsorption of carbon dioxide from air. The presence of carbonate in NaOH eluents often compromises the performance of an ion chromatographic method through an undesirable chromatographic baseline drift during the hydroxide gradient and even irreproducible retention times of target analytes.

A breakthrough in the routine practice of ion chromatography occurred when the EG40 Eluent Generator was introduced commercially in 1998. The EG40, based on the recently developed high-pressure electrolytic eluent generation technology, produced high-purity KOH or methanesulfonic acid (MSA) eluents on-line by pumping deionized water through a KOH or an MSA eluent generator cartridge (EGC). To generate a KOH eluent, deionized water is pumped through the KOH generation chamber and a current is applied between the device anode and cathode to induce the electrolysis of water as illustrated in Figure 1.

Under the electric field, potassium ions in the electrolyte reservoir migrate across the cation-exchange connector into the KOH generation chamber and combine with hydroxide ions generated at the cathode to produce a KOH solution. The concentration of KOH is controlled accurately and precisely by controlling the applied current and the flow rate of deionized water. The high-purity KOH solution generated on-line is an ideal eluent for ion chromatographic separations.

Over the years, the concept of electrolytic eluent generation has been extended to the on-line generation of other high-purity eluents used in ion chromatographic separations. In 2005, EGC-K₂CO₃ cartridges and electrolytic pH modifier (EPM) products were introduced to generate potassium carbonate and bicarbonate eluents electrolytically to make it easier to performance ion chromatographic separations where those eluents are used. In 2010, the capillary EGC-KOH and EGC-MSA cartridges designed specifically for capillary-scale ion chromatographic separations were introduced. In 2018, the dual-EG technology for generating potassium hydroxide (KOH) and potassium methanesulfonate (KMSA) eluents electrolytically was introduced to provide ease-of-use and improved reproducibility for determination of complex carbohydrates in the state-of-art Dionex^TM ICS-6000 Reagent-Free Ion Chromatography (RFIC^TM) systems.

RFIC systems are a culmination of more than 45 years of innovative technology developments in electrolytic eluent generators, continuously regenerated trap columns, high-performance anion and cation exchange columns, and electrolytic eluent suppressors by Thermo Fisher Scientific. RFIC systems have fundamentally changed how ion chromatography is practiced in laboratories globally and RFIC systems makes it very easy and convenient to perform a wide range of ion chromatographic separations by utilizing the €œJust Add Water€ the electrolytic eluent generation technology –see how here.