Column chromatography

Separation Technique : column chromatography

1. COLUMN CHROMATOGRAPHY Jeneesha Jude MSc .chemistry

2. Useful method for the separation and purification of both solids and liquids . Solid – liquid technique stationary phase – solid Mobile phase – liquid

3. Principle Adsorption Mixture of compounds dissolved in mobile phase is introduced into the column . Separation occurs because of the different rates at which the components are carried over the stationary phase by the mobile phase

4. Adsorption column chromatography , the adsorbent packed in glass column . Solvent – mobile phase , moves slowly through the packed column . Process of dissolving out the components from the adsorbent using a suitable solvent is called elution . This Solvent used as mobile phase – eluent .

5. Compound attracted more strongly by the mobile phase will move rapidly through the column . Compound more strongly attracted to the stationary phase will move slowly through the column

6. EXPERIMENTAL ASPECTS OF COLUMN CHROMATOGRAPHY ADSORBENTS : silica ,alumina, calcium carbonate , calcium phosphate , magnesia and starch Alumina suitable for chromatography of less polar compounds . Silica gel suitable for compounds containing polar functional groups .

7. ADSORBENTS – CRITERIA Particles - spherical in shape , uniform in size Mechanical stability must be great enough to prevent the formation of fine dust which might deposit in the channels of packing . Don’t react chemically either with eluent or with sample . Useful for separating wide variety of compounds. Inexpensive and freely available

8. SELECTION OF STATIONARY PHASE Removal of impurities Number of components to be separated Length of column used Affinity difference between compenents Quantity of adsorbent used

9. SELECTION OF MOBILE PHASE Acts as solvent , developer and eluent As developing agent To remove pure component out of the column – as eluent Based on solubility – solvent selection Polarity – important factor

10. DIFFERENT MOBILE PHASE USED Petroleum ether Carbon tetrachloride Cyclohexane Ether Ester Acetone Benzene Water

11. COLUMN CHARACTERISTICS Support stationary phase Column must be of good quality – neutral glass column dimensions : length and diameter ratio (10:1) Better separation : long narrow column because number of plates will be more.

12. PREPARTION OF COLUMN Consists of glass tube with bottom portion of the column – packed with cotton / glass wool Above which adsorbent is packed . After packing , paper disk is kept on the top , so that the adsorbent layer is not disturbed during the introduction of mobile phase .

13. PACKING TECHNIQUES OF ADSORBENTS DRY PACKING WET PACKING THE PROCESS An adsorbent column is prepared by packing a long glass tube with suitable adsorbent solution of the mixture of the components (say a,b,c ) in suitable solvents is introduced at the top of the column .

14. It percolates through the adsorbent column , different components adsorbed to different extend . Most readily adsorbed constituent(say a) is held at the top . Other (say b and c) of decreasing adsorbabilities are held up at different zones or bands down the column in the same order [say b and then c] This partial separation is improvised by adding some amount of original solvent – development of chromatogram.

15. Individual components are extracted from the adsorbent by a suitable solvent( eluent ). Most weakly adsorbed component (c) emerges first which is at the bottom of the column . Most strongly adsorbed one (a ) comes out last w hich was at the top of the column . Pure components are then recovered by removing the solvent by suitable method .

16. APPLICATIONS Used for separation of two or more similar organic components of a mixture Identification , separation and purification of natural products. Used for identification of various industrial products Separation of protein mixture.

17. Advantages of CC Any type and any quantity of mixture can be separated . Wider choice of mobile phase DISADVANTAGES OF CC Time consuming More amount of mobile phase is required .

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