high-pressure electrolytic carbonate eluent generation...

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

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., 4 µm) provides new opportunities to perform fast and high resolution

IC separations.

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 charge-

selective 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., 4 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., 4 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 3000 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 5000 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.

FIGURE 3. Block diagram of a typical RFIC system using Dionex EGC

500 carbonate eluent generator and Dionex EPM 500 electrolytic pH

modifier.

FIGURE 1. Electrolytic generation of K2CO3 eluents using a high-

pressure Dionex EGC 500 K2CO3 cartridge.

FIGURE 2. Electrolytic Generation of K2CO3/KHCO3 eluents using a

Dionex EGC 500 K2CO3 cartridge and Dionex EPM 500 modifier.

FIGURE 4. Separation of seven common anions on a 4 mm Dionex

IonPac AS22-Fast-4 µm column.

FIGURE 5. Separation of seven common anions on a 4 mm Dionex

IonPac AS22-Fast-4µm column Using an Dionex EGC 500 K2CO3

cartridge and an Dionex EPM 500 modifier.

When the Dionex EGC 500 K2CO3 cartridge is combined with a Thermo

Scientific Dionex EPM 500 electrolytic pH modifier, eluents of potassium

carbonate and bicarbonate can be generated electrolytically. As shown in

Figure 2, the Dionex EPM 500 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 500 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 6. Fast separation of seven common anions on a 4 mm Dionex

IonPac AS22-Fast-4µm column Using an Dionex EGC 500 K2CO3 cargridge

and a Dionex EPM 500 modifier.

FIGURE 7. Determination of inorganic anions in a drinking water

sample.

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This information is not intended to encourage use of these products in any manners that might infringe the

intellectual property rights of others.

The Dionex ICS-5000+ RFIC systems using Dionex EGC 500 K2CO3 cartridge and

Dionex EPM 500 modifier are capable of providing highly reproducible separation

of target analytes that are difficult to achieve using standard IC systems. Figure 5

shows an overlay of 100 consecutive high-resolution separations of seven common

anions obtained using a a 4 mm Dionex IonPac AS22-Fast-4µm column. We are

to achieve highly reproducible results with retention time RSD ranging from 0.03%

for phosphate to 0.06% for fluoride over the 100 consecutive runs.

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 K2CO3 solution,

which can be used as the eluent in ion chromatography. The concentration of

K2CO3 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 500 K2CO3 cartridge can be operated under pressures

up to 5000 psi.

Figure 3 shows the block diagram of key components in a typical RFIC system

using Thermo Scientific Dionex EGC 500 carbonate eluent generator and Dionex

EPM 500 electrolytic pH modifier. A high-pressure pump is used to deliver a

stream of deionized water into the Dionex EGC 500 K2CO3 eluent generator

cartridge where the high-purity K2CO3 eluent is generated electrolytically. A

Dionex EPM 500 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 500 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.

Experimental All experiments were performed using Thermo Scientific™ Dionex™ ICS-5000+

RFIC™ systems with electrolytic eluent generation. A typical Dionex ICS-5000+

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-5000+ 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 dual-

channel RFIC system supporting both conventional and capillary-scale IC

separations. The Dionex ICS-5000+ RFIC systems are fully supported by Thermo

Scientific™ Dionex™ Chromeleon™ Chromatography Data System (CDS) 7

software.

Figure 1 illustrates the principle of electrolytic generation of K2CO3 eluents. The

Thermo Scientific Dionex EGC 500 K2CO3 cartridge consists of an electrolyte

reservoir and two high-pressure eluent generation chambers, which are

connected in series. To generate a K2CO3 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,

Results and Discussion The use of the Dionex ICS-5000+ RFIC systems fitted with the new Dionex EGC

500 K2CO3 cartridge and the Dionex EPM 500 electrolytic pH modifier and new IC

columns packed with resins of smaller particle sizes (e.g., 4 µm) provides new

opportunities to perform fast and high resolution IC separations. Figure 4 shows

the separation of seven common anions on a 4-mm Thermo Scientific™ Dionex™

IonPac™ AS22-Fast-4 µm column using 4.5 mM K2CO3/ 1.4 mM KHCO3 (EG)

eluents prepared either manually or generated eletrolytically using a Dionex EGC

500 K2CO3 cartridge and an Dionex EPM 500 electrolytic pH modifier. We are

able to achieve essentially identical separation of the target analytes using both

eluents.

Column: Dionex IonPac AG22 –Fast-4µm

(4x30 mm),

Dionex IonPac AS22 –Fast-4µm

(4x150 mm)

Eluent: 4.5 mM K2CO3 / 1.4 mM

KHCO3 (EG)

Flow rate: 1.2 mL / min

Temperature: 30 o C

Loop: 10 L

Peak Concentration, mg/L

1. Fluoride 1

2. Chloride 5

3. Nitrite 5

4. Bromide 5

5. Nitrate 5

6. Phosphate 10

7. Sulfate 5

. -1

6

1

2

3

4 5 6 7

Eluent prepared

manually

Eluent from

EGC 500 K2CO3

/EPM 500

Minutes

µS

0 10


(4x30 mm),

Dionex IonPac AS22 –Fast-4µm

(4x150 mm)


KHCO3 (EG)


Temperature: 30 o C

Loop: 10 L


1. Fluoride 1

2. Chloride 5

3. Nitrite 5

4. Bromide 5

5. Nitrate 5

6. Phosphate 10

7. Sulfate 5

0 10

-1

5

Overlay of 100 consecutive runs

Retention time RSD:

0.03% (Phosphate) to 0.06% (Fluoride)

1

2

3

4 5

6

7

µS

Minutes

The Dionex ICS-5000+ RFIC system provides an ideal platform to perform fast

separation of common anions. Figure 6 shows the fast separation of common

anions using a 4 mm Dionex IonPac AS22-Fast-4µm column. By performing

separation at 1.5 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-5000+ RFIC system fitted with the Dionex EGC 500 K2CO3 cartridge

and Dionex EPM 500 electrolytic pH modifier is an ideal system for fast analysis

of drinking water samples.

0 10

0

140

µS


Retention time RSD:

0.03% (Sulfate) to 0.06% (Fluoride)

Peak area RSD:

0.06 % (Chloride) to 0.67% (Fluoride)

Column: Dionex IonPac AG22 –Fast- 4µm

(4x30 mm),

Dionex IonPac AS22 –Fast- 4µm

(4x150 mm)


KHCO3 (EG)


Temperature: 30 o C

Loop: 10 L

Peak Concentration, mg / L

1. Fluoride 0.5

2. Chloride 154.8

3. Nitrate 1.4

4. Sulfate 44.5

1

2

3

4

Minutes

- 20

0 10 -1

0

4


(4x30 mm),

Dionex IonPac AS22 –Fast-4 µm

(4x150 mm)


KHCO3 (EG)


Temperature: 30 o C

Loop: 10 L


1. Fluoride 1

2. Chloride 5

3. Nitrite 5

4. Bromide 5

5. Nitrate 5

6. Phosphate 10

7. Sulfate 5

µS

Minutes

1

2

3

5 4

6

7


Retention time RSD:

0.03% (Phosphate) to 0.1% (Fluoride)

Peak area RSD:

0.4 % (Bromide) to 0.9% (Nitrite)

OT71574-EN 0315S

high-pressure electrolytic carbonate eluent generation...

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