High-Pressure Electrolytic Carbonate Eluent Generation Devices and Their Applications in Ion Chromatography Systems Yan Liu, Zhongqing Lu, and Chris Pohl; Thermo Fisher Scientific, Sunnyvale, CA USA
Overview Purpose: In this work, new high-pressure electrolytic potassium carbonate and potassium bicarbonate eluent generation devices are developed. Methods: The new electrolytic eluent generation devices utilize the electrochemical processes involving the electrolysis of water and chargeselective transport of ions across ion exchange media to generate high-purity potassium carbonate and potassium bicarbonate solutions as eluents for use in ion chromatography systems. Results: The combined use of Reagent-Free Ion Chromatography (RFIC ) systems fitted with new high-pressure eluent generation devices and new IC columns packed with resins of smaller particle sizes (e.g., µm) provides new opportunities to perform fast and high resolution IC separations. Introduction Ion chromatography (IC) is a widely used analytical technique for determination of anionic and cationic analytes in various sample matrices. In modern IC systems, high purity acid, base, or salt eluents are generated electrolytically using deionized water as the carrier. The Reagent-Free Ion Chromatography (RFIC) systems with electrolytic eluent generation make it possible to perform a wide range of ion chromatographic separations using only deionized water as the carrier. For many applications, the RFIC systems provide improved performance with increased sensitivity and the flexibility to perform isocratic and gradient separations. In addition to saving time, labor, and operating costs, the RFIC systems eliminate errors and problems associated with manual eluent preparation and offer users the benefits of simplicity, ease of use, and improved method reproducibility. There is growing interest in the development and application of new IC columns packed with resins of smaller particle sizes (e.g., µm or smaller) since these columns bring out new opportunities to perform fast and high-resolution IC separations. The new smaller-particle-size IC columns typically yield pressures higher than psi, which is the maximum operating pressure of the current generation of electrolytic eluent generators. Therefore, there is a need to develop electrolytic eluent generators capable of operating at elevated pressures. Here, the authors describe the development of a new generation of electrolytic devices for generating high-purity potassium carbonate and potassium bicarbonate using deionized water as the carrier stream. The new electrolytic eluent generators can be operated under pressures up to psi. We will describe the principles and operation of the new electrolytic eluent generators, and demonstrate the advantages of using these devices to achieve fast and high resolution ion chromatographic separations. Experimental All experiments were performed using Thermo Scientific Dionex ICS- + RFIC systems with electrolytic eluent generation. A typical Dionex ICS- + system consists of a dual pump module (DP), an eluent generator (EG) module, and a detector/chromatography module (DC). The modular design of the Dionex ICS- + system allows users to quickly configure and customize components for a wide range of applications. The system can be configured as a dual-channel capillary RFIC system, a dual-channel conventional RFIC system, or a dualchannel RFIC system supporting both conventional and capillary-scale IC separations. The Dionex ICS- + RFIC systems are fully supported by Thermo Scientific Dionex Chromeleon Chromatography Data System (CDS) 7 software. Figure illustrates the principle of electrolytic generation of K CO eluents. The Thermo Scientific Dionex EGC K CO cartridge consists of an electrolyte reservoir and two high-pressure eluent generation chambers, which are connected in series. To generate a K CO solution, deionized water is pumped into the eluent generation chambers and a DC electrical current is applied to the anode and cathode of the device. Under the applied electrical field, High-Pressure Electrolytic Carbonate Eluent Generation Devices and Their Applications in Ion Chromatography Systems
potassium ions in the electrolyte reservoir migrate across the cation-exchange connector and combine with the hydroxide ions produced at the cathode through the reduction of water to form a KOH solution. In the meantime, carbonate ions migrate across the anion exchange connector and combine with H + ions produced at the anode through the oxidation of water to form a carbonic acid solution. The KOH solution reacts with the carbonic acid solution to form a K CO solution, which can be used as the eluent in ion chromatography. The concentration of K CO formed is directly proportional to the applied DC current and inversely proportional to the flow rate of DI water going through the eluent generation chamber. The Dionex EGC K CO cartridge can be operated under pressures up to psi. FIGURE. Electrolytic generation of K CO eluents using a highpressure Dionex EGC K CO cartridge. When the Dionex EGC K CO cartridge is combined with a Thermo Scientific Dionex EPM electrolytic ph modifier, eluents of potassium carbonate and bicarbonate can be generated electrolytically. As shown in Figure, the Dionex EPM modifier consists of a cation-exchange bed that is fitted with an anode at its outlet. The inlet end of the device is connected to a cathode through the cation exchange connector. A DC current is applied to the Dionex EPM modifier to remove a controlled amount of potassium ions which are forced to migrate across the cation-exchange connector. The displaced potassium ions move toward the cathode and combine with hydroxide ions to form a solution of potassium hydroxide, which is directed to waste. In the meantime, hydronium ions generated at the anode converts carbonate into bicarbonate. Therefore, by controlling the applied current, the ph of the incoming potassium carbonate eluent can be modified to form a potassium carbonate and bicarbonate solution for use as the eluent in IC separations. Figure shows the block diagram of key components in a typical RFIC system using Thermo Scientific Dionex EGC carbonate eluent generator and Dionex EPM electrolytic ph modifier. A high-pressure pump is used to deliver a stream of deionized water into the Dionex EGC K CO eluent generator cartridge where the high-purity K CO eluent is generated electrolytically. A Dionex EPM electrolytic ph modifier is the used to convert a controlled amount of carbonate into bicarbonate in the eluent. A high-pressure degasser containing a gas permeable tubing is used to remove hydrogen or oxygen gas formed electrolytically. There are several other downstream system components including a sample injector, a separation column, and an electrolytic suppressor. In the system shown, the conductivity detector effluent is routed through the regenerant chambers of the electrolytic suppressor, the Dionex EPM modifier, and the high-pressure degasser assembly before going to waste. Therefore, the RFIC system makes it possible to perform the entire IC separation process using deionized water as the carrier. Thermo Scientifi c Poster Note PITTCON PN77-EN S
FIGURE. Electrolytic Generation of K CO /KHCO eluents using a Dionex EGC K CO cartridge and Dionex EPM modifier. FIGURE. Block diagram of a typical RFIC system using Dionex EGC carbonate eluent generator and Dionex EPM electrolytic ph modifier. Results and Discussion The use of the Dionex ICS- + RFIC systems fitted with the new Dionex EGC K CO cartridge and the Dionex EPM electrolytic ph modifier and new IC columns packed with resins of smaller particle sizes (e.g., µm) provides new opportunities to perform fast and high resolution IC separations. Figure shows the separation of seven common anions on a -mm Thermo Scientific Dionex IonPac AS-Fast- µm column using. mm K CO /. mm KHCO (EG) eluents prepared either manually or generated eletrolytically using a Dionex EGC K CO cartridge and an Dionex EPM electrolytic ph modifier. We are able to achieve essentially identical separation of the target analytes using both eluents. High-Pressure Electrolytic Carbonate Eluent Generation Devices and Their Applications in Ion Chromatography Systems
FIGURE. Separation of seven common anions on a mm Dionex IonPac AS-Fast- µm column. 6 6 7 Eluent from EGC K CO /EPM Eluent prepared manually - Minutes. Dionex IonPac AG Fast-µm (x mm), Dionex IonPac AS Fast-µm (x mm). mm K CO /. mm KHCO (EG). ml / min o C L Concentration, mg/l. Fluoride. Chloride. Nitrite. Bromide. Nitrate 6. Phosphate 7. Sulfate The Dionex ICS- + RFIC systems using Dionex EGC K CO cartridge and Dionex EPM modifier are capable of providing highly reproducible separation of target analytes that are difficult to achieve using standard IC systems. Figure shows an overlay of consecutive high-resolution separations of seven common anions obtained using a a mm Dionex IonPac AS-Fast-µm column. We are to achieve highly reproducible results with retention time RSD ranging from.% for phosphate to.6% for fluoride over the consecutive runs. FIGURE. Separation of seven common anions on a mm Dionex IonPac AS-Fast-µm column Using an Dionex EGC K CO cartridge and an Dionex EPM modifier. - Overlay of consecutive runs Retention time RSD:.% (Phosphate) to.6% (Fluoride) 6. Fluoride. Chloride. Nitrite. Bromide. Nitrate Minutes 6. Phosphate 7. Sulfate 7 Dionex IonPac AG Fast-µm (x mm), Dionex IonPac AS Fast-µm (x mm). mm K CO /. mm KHCO (EG). ml / min o C L Concentration, mg/l The Dionex ICS- + RFIC system provides an ideal platform to perform fast separation of common anions. Figure 6 shows the fast separation of common anions using a mm Dionex IonPac AS-Fast-µm column. By performing separation at. ml/min, six common anions were separated in less than 6 min while maintaining sufficient resolution of target analytes and excellent reproducibility. Figure 7 shows the highly reproducible determination of common anions in a drinking water sample. These results indicate that the Dionex ICS- + RFIC system fitted with the Dionex EGC K CO cartridge and Dionex EPM electrolytic ph modifier is an ideal system for fast analysis of drinking water samples. Thermo Scientifi c Poster Note PITTCON PN77-EN S
FIGURE 6. Fast separation of seven common anions on a mm Dionex IonPac AS-Fast-µm column Using an Dionex EGC K CO cargridge and a Dionex EPM modifier. Overlay of consecutive runs Retention time RSD:.% (Phosphate) to.% (Fluoride) area RSD:. % (Bromide) to.9% (Nitrite) - Minutes 6 7. Fluoride. Chloride. Nitrite. Bromide. Nitrate 6. Phosphate 7. Sulfate Dionex IonPac AG Fast-µm (x mm), Dionex IonPac AS Fast- µm (x mm). mm K CO /. mm KHCO (EG). ml / min o C L Concentration, mg/l FIGURE 7. Determination of inorganic anions in a drinking water sample. Overlay of consecutive runs Retention time RSD:.% (Sulfate) to.6% (Fluoride) area RSD:.6 % (Chloride) to.67% (Fluoride) Dionex IonPac AG Fast- µm (x mm), Dionex IonPac AS Fast- µm (x mm). mm K CO /. mm KHCO (EG). ml / min o C L Concentration, mg / L. Fluoride. - Minutes. Chloride.8. Nitrate.. Sulfate. Conclusion The development of electrolytic eluent generation technology and RFIC systems has fundamentally changed the practice of ion chromatography RFIC systems offer significant benefits in terms of ease of use and improved performance of IC methods The combined use of RFIC systems fitted new high-pressure EGC cartridges and new IC columns packed with resins of smaller particle sizes (e.g., µm) provides new opportunities to perform fast and high resolution IC separations. www.thermoscientific.com/chromatography Thermo Fisher Scientifi c Inc. All rights reserved. ISO is a trademark of the International Standards Organization. All other trademarks are the property of Thermo Fisher Scientifi c and its subsidiaries. This information is presented as an example of the capabilities of Thermo Fisher Scientifi c products. It is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others. Specifi cations, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. Thermo Fisher Scientifi c, Sunnyvale, CA USA is ISO 9 Certifi ed. Africa + Australia +6 977 Austria + 8 8 6 Belgium + 7 Brazil + 7 Canada + 8 87 China 8 8 8 (free call domestic) 6 8 PN77-EN S Denmark + 7 6 6 Europe-Other + Finland +8 9 9 France + 6 9 8 Germany +9 6 8 India +9 67 99 Italy +9 9 9 Japan +8 6 688 Korea +8 86 Latin America + 6 688 87 Middle East + Netherlands + 76 79 New Zealand +6 9 98 67 Norway +6 8 6 68 Russia/CIS + Singapore +6 689 9 Sweden +6 8 6 68 Switzerland + 6 76 77 Taiwan +886 87 66 UK/Ireland + USA + 8 7