Q.22 The stationary phase of cation–exchange chromatography can be
(A) DEAE–cellulose
(B) CM–cellulose
(C) Sephadex G–50
(D) Heparin–Sepharose
Cation-Exchange Chromatography Stationary Phase: CSIR NET Solved Question
The correct answer to the question “The stationary phase of cation-exchange chromatography can be” is (B) CM-cellulose. Cation-exchange chromatography separates positively charged molecules using a negatively charged stationary phase, and CM-cellulose fits this role perfectly.
Option Analysis
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(A) DEAE-cellulose: This is a positively charged anion exchanger with diethylaminoethyl groups, binding negatively charged molecules. It cannot serve as a stationary phase for cation-exchange chromatography.
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(B) CM-cellulose: Carboxymethyl cellulose has negatively charged carboxymethyl (-CH2COOH) groups at neutral pH, attracting cations. This makes it the ideal weak cation exchanger.
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(C) Sephadex G-50: This is a neutral dextran gel used for size-exclusion (gel filtration) chromatography, separating by molecular size rather than charge.
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(D) Heparin-Sepharose: Heparin provides affinity binding for specific proteins like coagulation factors, not general cation exchange.
Cation-exchange chromatography stationary phase plays a crucial role in protein purification for CSIR NET life sciences aspirants. This technique separates cations based on charge interactions, with CM-cellulose emerging as the key matrix.
Principle of Cation Exchange
In cation-exchange chromatography, the stationary phase carries negative charges to bind positively charged analytes. Elution occurs via increasing salt concentration or pH adjustment, releasing bound molecules by charge neutralization.
Why CM-Cellulose?
CM-cellulose, or carboxymethyl cellulose, features -CH2OCH2COO⁻ groups that ionize negatively at pH 4-10. This weak cation exchanger excels in separating basic proteins, commonly used in biochemistry labs.
Comparing Options
| Option | Type | Charge | Application |
|---|---|---|---|
| DEAE-cellulose | Anion exchanger | Positive | Acidic protein separation |
| CM-cellulose | Cation exchanger | Negative | Basic protein purification |
| Sephadex G-50 | Size-exclusion | Neutral | Molecular weight fractionation |
| Heparin-Sepharose | Affinity | Specific | Targeted protein binding |
CSIR NET Exam Tips
For questions like Q.22, recall that cation exchangers (e.g., CM, SP) are negative, while anion exchangers (e.g., DEAE, Q) are positive. Practice with protein pI values to predict binding.
