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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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
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
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
Overlay of 30 consecutive runs
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)
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 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
Column: Dionex IonPac AG22 –Fast-4µm
(4x30 mm),
Dionex IonPac AS22 –Fast-4 µm
(4x150 mm)
Eluent: 4.5 mM K2CO3 / 1.4 mM
KHCO3 (EG)
Flow rate: 1.5 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
µS
Minutes
1
2
3
5 4
6
7
Overlay of 30 consecutive runs
Retention time RSD:
0.03% (Phosphate) to 0.1% (Fluoride)
Peak area RSD:
0.4 % (Bromide) to 0.9% (Nitrite)
OT71574-EN 0315S
