Paper chromatography has evolved over the years and has found widespread applications in separation of molecules of different polarities. Innumerable applications have been reported in analysis of different classes of compounds such as:
- Amino acids and organic acids
- Proteins and peptides
- Natural and artificial pigments
- Inorganic cations
- Plant extracts
Typical applications in key areas are briefly outlined here
In a chemical reaction over a period of time the concentration of reactants decreases whereas the concentration of products increases. Developing the chromatogram over different time intervals by spotting the reactants can give a fair idea on the progress of reaction. Traditionally the technique was used for qualitative monitoring but availability of densitometers made quantitative estimations possible. However, rapid methods using spectroscopic techniques are limiting the application of paper chromatography as a reaction monitoring option.
Isolation & Purification
Paper chromatography has been put to use as a purification and isolation technique for components of mixtures. The separated components on the paper are cut, dissolved in suitable solvents and their absorption characterised at specific wavelengths using spectrophotometric methods. This approach is being superseded by techniques such as Preparative HPLC.
Paper chromatography has been primaly used for analysis of food colours in synthetic drinks and beverages, ice creams, jams &jellies, sweets,etc.Colours both natural and synthetic are added to foods to improve their acceptability and to make them more popular. Only edible colours are permitted for use so identification and quantification becomes all the more important to ensure that no non- permitted colouring agents are added to the foods.
A forensic scientist is often faced with a severe limitation on the quantity of sample available for analysis Paper chromatography offers a viable analysis option for samples available in milligrams or microlitre quantities.
The major applications are for identification and comparison against reference standards for drugs and their metabolites in viscera, explosive residues from blast sites, inks used in forgery of documents and paint pigments investigations in hit and run road accident cases.
Paper chromatography provides useful information on development of new drug molecules, reaction completion and progress of manufacturing processes. It also offers a cost-effective alternative to monitoring the active ingredients in drug forms administered in bioanalytical studies. Its main contribution is when the quantity of sample available is in minute amounts.
In a subsequent article some reasons will be presented for justification of continued popularity of paper chromatography in the face of tough competition from more advanced chromatographic techniques.