Ion-exchange chromatography (or ion chromatography) is a process that allows the separation of ions and polar molecules based on their charge. It can be used for almost any kind of charged molecule including large proteins, small nucleotides and amino acids. The solution to be injected is usually called a sample, and the individually separated components are called analytes. It is often used in protein purification, water analysis, and quality control.
Ion-exchange chromatography retains analyte molecules on the column based on coulombic (ionic) interactions. The stationary phase surface displays ionic functional groups (R-X) that interact with analyte ions of opposite charge. This type of chromatography is further subdivided into cation exchange chromatography and anion exchange chromatography. The ionic compound consisting of the cationic species M+ and the anionic species B- can be retained by the stationary phase.
Cation exchange chromatography retains positively charged cations because the stationary phase displays a negatively charged functional group:
Anion exchange chromatography retains anions using positively charged functional group:
Note that the ion strength of either C+ or A- in the mobile phase can be adjusted to shift the equilibrium position and thus retention time.
The ion chromatogram shows a typical chromatogram obtained with an anion exchange column. (Adapted from Wikipedia)
The Dionex Ion-Exchange Chromatograph we have is an IC25 Ion Chromatograph attached with an AS50 Autosampler, an EG40 Eluent Generator, and an LC25 Chromatography Oven.
The Dionex IC25 Ion Chromatograph performs isocratic ion analyses using conductivity detection. The IC25 integrates pump and detector functions in a single instrument. The microprocessor-based, dual-piston, variable-speed, delivery system pumps eluents at precisely controlled flow rates. The IC25 electronics provide sensitive, accurate detection and quantification of ionic analytes in liquid and ion chromatography. This is especially useful for analytes that lack UV chromophores and cannot be determined with adequate sensitivity by UV absorbance. A Digital Signal Processor (DSP) provides high speed control of pump flow and pressure.
IC25 Ion Chromatograph
- Pump: Dual-piston, variable speed stroke of 100 µL; user-selectable constant pressure or constant flow feedback control
- Flow Rate: 0.04 to 10.0 mL/min, linearly variable in increments of 0.01 mL/min
- Operating Pressure: 21 MPa (3000 psi) maximum
- Pressure Resolution: 0.07 MPa (10 psi)
- High Pressure Limit: 0 to 35 MPa (0 to 5000 psi) in increments of 0.05 MPa (7.25 psi); trips instantaneously
- Low Pressure Limit: 0 to 35 MPa (0 to 5000 psi) in increments of 0.05 MPa (7.25 psi); trips after a timeout of 0.4 mL
- Delay Volume: Approximately 700 µL
Conductivity Detector
- Range: 0.01 µS to 3000 µS, full-scale
- Temperature Compensation 0.0 to 3.0% per ºC
- Cell Drive: Variable 8 kHz square wave
- Control Modes: Local or remote by relay contact-closures or the DX-LAN interface