Question

Proof read lab report on theory of column chromatography. We just did TLC last week and now we are doing column.  

Some key points in my background need to include.  

Describe Column chromatography and its applications

Choosing solvents for column chromatography

sample and column size

packing column two methods, adding sample, eluting column, and monitoring column

Column chromatography is used to purify individual chemical compounds from mixtures. Generally, it is used in a glass tube from 5 mm to 50 mm and a height of 5 cm to 1 m. Two methods that can be used are the dry method which the column is filled with a dry stationary phase powder and followed by the mobile phase, then flushed through the column until wet. And the wet method, in which a slurry is prepared with the stationary phase powder and then poured into the column. A solution of organic material is carefully added to the top of the stationary phase. The layer is then topped with small amount of sand, cotton, or glass wool to protect the shape.

The solvent that is generally chosen for column chromatography depends on the polarity of what is being separated. Hexane or cyclohexane is often used for non-polar compounds.   Ethyl acetate is often used for polar compounds. Similar to TLC, the solvents can be mixed in a ratio to separate the chemicals with better results.

This what I have so far. Please make comments and suggestions on how I could improve my theory.

Thanks

Answer 1

Points you can include :
Working Principle of column : Differential adsorption
seperation based on property : Polarity and hydrophobicity.
Working : (you can include adding sample, eluting column & monitoring column down below)
The stationary phase acts as adsorbent (alumina or silica gel) which is usually a
solid while mobile phase is a liquid. After the mixture is injected each one undergoes adsorption in a
slightly different way and spends more or less time in either the solid or the liquid phase depending
on their relative polarities. (more discussed in Adding sample, eluting column & monitoring column)
Applications :
To isolate active components, to estimate drug compositions in formulations.
Choosing solvents for column chromatography : The column has to be neutral, it should not make the
column neither acidic nor basic.
Ex : Toluene, Alcohols, benzene, acetone etc.
Sample and column size :
Length to diameter can be upto 30:1 ratios. However the length should
be prominently high compared to diameter since it is vertical column and it depends on factors like
the quantity of sample, type of stationary phase used, pressure, temperature etc.
The dry and wet packing techniques you have mentioned in your report come under this (column prep)
Adding sample, eluting column & monitoring column :
The sample has mixture of components dissolved in mobile phase which is injected into the column
and from there samples are separated individually by elution process. Polar compounds interact
with the adsorbent more strongly than non-polar ones. So polar compounds elute first and later non-polar compounds. At end of the column the analytes are analyzed by UV-VIS detector or any other
detector and the whole process is monitored by a computer.