ion exchange chromatography - ksufac.ksu.edu.sa/sites/default/files/bch_332_lecture_11.pdf•ion...
Post on 18-Jul-2020
53 Views
Preview:
TRANSCRIPT
Ion Exchange Chromatography
BCH 332 lecture 11
1
• Ion exchange chromatography is a form of adsorption chromatography in which charged proteins or other biomolecules are exchanged for small ions of like charge originating in salts (e.g. Na+, Cl−).
• These ions are attached to chemical structures on the surface of the stationary phase called ion exchange groups or ion exchangers.
2
• Two types of ion exchanger are common in biochemistry;
• Anion exchangers (which exchange negatively charged ions or anions) and
• Cation exchangers (which exchange positively charged ions or cations).
3
4
5
6
• Some ion exchangers are regarded as weak, that is functioning best over a comparatively narrow pH range, while others are strong, that is functioning over a wider pH range. Exchangers with quaternary amino or sulfonic acid groups behave as strong anion and cationexchangers, respectively, while aromatic/aliphatic amino and carboxylic acid groups are weak anion and cation exchangers, respectively.
• Choice of ion exchange stationary phase is heavily influenced by knowledge of the pI of the protein of interest.
7
8
• Desalting is carried out before ion exchange either by gel filtration chromatography , by dialysis or by centrifugal filtration.
• Elution of bound proteins is achieved by reversing the process of binding and, again, exchanging a counterion for protein.
• This is usually carried out by applying a large excess of a salt (e.g. NaCl) containing the counterion in the mobile phase.
• Because proteins have different net charge, they may bind to an ion exchanger at a given pH with a variety of strengths, that is some proteins may bind strongly whilst others bind weakly or not at all.
• We can take advantage of this to separate proteins by applying salt in a continuous gradient. Weakly bound proteins will elute first from such a system while strongly bound proteins elute later.
9
• Mobile phase Acids, alkalis, buffer.
• Stationary phase The ionic compound consisting of the cationic species (M+) and the anionic species (B-)
• Elution - Components of mixture separate & move down the column at different rates depending upon the affinity of the ion for ion exchanger. The eluates are collected at different stages
• Analysis of the eluate (Spectrophotometric)
10
11
12
Selection of an Ion Exchanger
13
Selection of an Ion Exchanger
14
15
• Below the isoelectric pH the protein has a positive charge and binds to a cation exchanger.
• Above the isoelectric pH the protein has a negative charge and binds to an anion exchanger.
16
Choice of Buffer
• Cationic buffer should be used with anion exchanger.
• Anionic buffer should be used with cation exchanger.
17
• The basic process of chromatography using ion exchange can be represented in 4 steps:
1. Equilibration
2. Sample application and wash
3. Elution
4. Regeneration
18
19
20
21
22
APPLICATIONS
• For extraction of enzymes from tissues.
• Separation of sugars, amino acids and proteins.
• Ion exchange column in HPLC.
23
top related