Ion Exchange

Ion Exchange Chromatography separates analytes according to their net charge under specific pH and ionic strength conditions. The stationary phase carries charged functional groups — either positive (anion exchanger) or negative (cation exchanger) — which interact reversibly with oppositely charged solutes.
By gradually increasing the ionic strength or changing the pH of the mobile phase, analytes are selectively displaced according to their charge density and binding affinity. This enables precise resolution of complex biological samples, protein isoforms, and charged macromolecules.
IEX is an indispensable tool in biochemistry, biotechnology, and pharmaceutical purification, providing high capacity, reproducibility, and scalability for both analytical and preparative separations.

Introduction

Ion Exchange Chromatography is one of the most established modes of liquid chromatography for the purification and characterization of charged compounds. It offers superior selectivity and loading capacity compared to non-ionic modes, while maintaining mild, aqueous conditions that preserve biological activity.
The technique is compatible with proteins, peptides, amino acids, nucleic acids, and ionic polymers, and can be adapted for gradient or stepwise elution to optimize resolution and recovery.

Stationary Phase

The stationary phase in IEX consists of silica- or polymer-based particles functionalized with charged groups that act as ion exchangers.

  • Cation exchangers carry negatively charged groups such as sulfonic acid (strong cation exchanger, SCX) or carboxylic acid (weak cation exchanger, WCX) and retain positively charged analytes.

  • Anion exchangers carry positively charged groups such as quaternary amines (strong anion exchanger, SAX) or secondary/tertiary amines (weak anion exchanger, WAX) and retain negatively charged analytes.

Silica-based IEX materials provide high efficiency and mechanical stability, while polymeric phases offer superior chemical resistance and broader pH tolerance. The choice of matrix and functional group determines binding strength, selectivity, and operating conditions, allowing fine-tuned control for diverse analytical or preparative applications.

Mobile Phase

The mobile phase in IEX is typically aqueous, containing a buffer system that controls pH and ionic strength. Common buffers include phosphate, Tris, acetate, or MES, depending on the desired pH range.
Elution is usually achieved by increasing salt concentration (e.g., NaCl gradient) or adjusting pH to alter analyte charge states and weaken electrostatic binding. For analytical IEX, volatile buffers such as ammonium acetate or ammonium bicarbonate are preferred for LC-MS compatibility.
All mobile phase components should be of high purity and properly filtered to maintain column performance and reproducibility.

Retention Mechanism

Retention in Ion Exchange Chromatography is governed by Coulombic interactions between oppositely charged species. Analytes with a higher charge density or stronger electrostatic affinity are retained longer, while weakly charged molecules elute earlier.
Adjusting mobile phase pH, buffer composition, or ionic strength directly influences retention and selectivity. This tunable mechanism provides precise control over resolution, capacity, and elution order, making IEX one of the most versatile separation techniques for charged biomolecules and synthetic compounds.

Recommended Phases

Show all suitable Dr. Maisch columns

Columns suitable for Ion Exchange

Name Particle Sizes Carbon Load Pore Size
Adsorbosphere SAX 3 – 10 µm 8 % 100 Å
Adsorbosphere XL Carbohydrate AX 7 µm 100 Å
Adsorbosphere XL SAX 3 – 10 µm 8 % 100 Å
Adsorbosphere XL SCX 3 – 10 µm 9 % 100 Å
Allsphere SAX 3 – 10 µm 8 % 100 Å
Allsphere SCX 3 – 10 µm 9 % 100 Å
Equisil SAX 5 µm 5 % 120 Å
Equisil SCX 5 µm 5 % 120 Å
Equisorb SAX 3 – 10 µm 8 % 80 Å
Equisorb SCX 3 – 10 µm 10 % 80 Å
Exsil 80 SAX 5 – 10 µm 80 Å
Exsil 80 SCX 3 – 10 µm 80 Å
Exsil 100 SAX 5 – 10 µm 100 Å
Exsil 100 SCX 3 – 12 µm 100 Å
Exsil Pure 120 Phenyl-SCX 5 µm 120 Å
Exsil Pure 120 SAX 1.5 – 10 µm 120 Å
Exsil Pure 120 SCX 1.5 – 10 µm 120 Å
Exsil 300 SAX 5 µm 300 Å
Exsil Avanti SAX 5 µm 130 Å
Exsil Avanti SCX 5 µm 130 Å
Exsil Clasico SAX 8 µm 90 Å
Exsil Clasico SCX 5 µm 90 Å
GromSil Anion 5 µm
GromSil 80 SAX 5 – 10 µm 80 Å
GromSil 80 SCX 3 – 10 µm 80 Å
GromSil 100 SAX 5 – 10 µm 100 Å
GromSil 100 SCX 5 – 10 µm 100 Å
Macrosphere 300 SAX 5 µm 300 Å
Macrosphere 300 SCX 5 µm 300 Å
Macrosphere 300 WCX 7 µm 300 Å
ReproSil Mixed-Mode Amino-C8 3 – 5 µm 11 % 100 Å
ReproSil Mixed-Mode Amino-C18 3 – 5 µm 17 % 100 Å
ReproSil Mixed-Mode C18-Acid 5 – 10 µm 20 % 100 Å
Reprospher 120 SAX-C8 10 µm 120 Å
Reprospher 120 SCX-C8 10 µm 120 Å
Platinum SAX 3 – 5 µm 100 Å
Platinum SCX 3 – 5 µm 100 Å
Repromer 1000 AX 10 µm 1 000 Å
Repromer AX 5 – 15 µm 100 Å
Repromer AX-2 10 µm 100 Å
Repromer AXS 7 µm 100 Å
Repromer CAT 7 µm 100 Å
Repromer SCX 10 µm 100 Å
Repromer SCX 300 7 µm 300 Å
RepromerQ 10 – 30 µm N/A
ReproPart SAX 10 µm 10 % 125 Å
ReproPart SCX 10 µm 10 % 125 Å
ReproSil 70 SCX 5 – 10 µm 20 % 70 Å
ReproSil 80 SAX 3 – 10 µm 4 % 80 Å
ReproSil 80 SAX-2 5 µm 4 % 80 Å
ReproSil 80 SCX 3 – 10 µm 10 % 80 Å
ReproSil 100 CAT 3 – 7 µm 100 Å
ReproSil 100 SCX 3 – 10 µm 100 Å
ReproSil 300 SAX 5 µm 300 Å
ReproSil Saphir 100 SAX 5 µm 6 % 100 Å
ReproSil Saphir 100 SCX 3 – 10 µm 6 % 100 Å
ReproSil Saphir 300 CM 5 – 10 µm 3 % 300 Å
ReproSil Saphir 300 SCX 5 – 15 µm 6 % 300 Å
ReproSil Star SAX 5 – 7 µm 7 % 200 Å
ReproSil Star SAX-2 5 µm 7 % 200 Å
ReproSil Star SAX-3 5 µm 300 Å
ReproSil Star SCX 5 µm 200 Å
ReproSil-XR 120 SAX 3 – 5 µm 8 % 120 Å
ReproSil-XR 120 SCX 3 – 5 µm 8 % 120 Å
ReproSil-XR 300 SCX 3 – 5 µm 4 % 300 Å
Reprospher 100 C18-WCX 3 – 10 µm 17 % 100 Å
Reprospher Acidosil-C 5 – 10 µm 7 % 100 Å
Reprospher Acidosil-S 5 – 10 µm 13 % 100 Å
Reprospher 200 SAX 3 – 50 µm 7 % 200 Å
Ultrasep ES Phenyl-SCX75 5 µm 100 Å
Ultrasep ES SAX QCM 7 µm 100 Å
Ultrasep ES SAX-W 5 – 7 µm 100 Å
Ultrasep ES SAX-W33 5 µm 100 Å
Ultrasep ES SCXPM 5 µm 100 Å
Ultrasep SAX-2 5 µm
HILIC Ion Exclusion

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