Question

Thin-layer chromatography is a relatively low tech chromatographic method (no expensive instrumentation is required). What are the potential advantages of this method over gas chromatography or high pressure liquid chromatography?

Answer 1

Thin layer chromatography (TLC) is a chromatographic technique used to separate the components of a mixture using a thin stationary phase supported by an inert backing. It may be performed on the analytical scale as a means of monitoring the progress of a reaction, or on the preparative scale to purify small amounts of a compound. TLC is an analytical tool widely used because of its simplicity, relative low cost, high sensitivity, and speed of separation.TLC functions on the same principle as all chromatography: a compound will have different affinities for the mobile and stationary phases, and this affects the speed at which it migrates. The goal of TLC is to obtain well defined, well separated spots.
VARIOUS APPLICATIONS OF THIN LAYER CHROMATOGRAPHY (TLC) ARE AS FOLLOWS:
1)Purity of any sample : Purity of sample can be carried out with TLC. Direct comparison is done between the sample and the standard or authentic sample; if any impurity is detected, then it shows extra spots and this can be detected easily.
2)Identification of compounds: Thin layer chromatography can be employed in purification, isolation and identification of natural products like volatile oil or essential oil, fixed oil, waxes, terpenes, alkaloids, glycosides, steriods etc.
3)Examination of reactions: Reaction mixture can be examined by Thin layer chromatography to access whether the reaction is complete or not. This method is also used in checking other separational processes and purification processes like distillation, molecular distillation etc.
4)Biochemical analysis: TLC is extremely useful in isolation or separation of biochemical metabolites or constituent from its body fluids, blood plasma, serum, urine etc.
5)In chemistry: TLC methodology is increasingly used in chemistry for the separation and identification of compounds which are closely related to each other. It is also used for identification of cations and anions in inorganic chemistry.
6)In pharmaceutical industry: Various pharmacopoeias have adopted TLC technique for detection of impurity in a pharmacopoeial chemical.
Various medicines like hypnotics, sedatives, anticonvulsant tranquillisers, antihistaminics, analgesics, local anaesthetics, steroida have been tested qualitatively by TLC method.
One of the most important application of TLC is in separation of multicomponent pharmaceutical formulations.
7)In food and cosmetic industry , TLC method is used for separation and identification of colours, preservatives, sweetening agent, and various cosmetic products.

SOME OF THE ADVANTAGES OF THIN LAYER CHROMATOGRAPHY over GC ARE AS FOLLOWS:-

1)Less equipment is required.
2)Very little time for separation is required.
3)It is more sensitive.
4)The lower detection limit of analytical sample in TLC is approximately one decimal lower than that is paper chromatography and very small quantities of sample is sufficient for analysis.
5)Spraying with corrosive agents for identification is also permitted which is not possible in paper chromatography as cellulose gets destroyed.
6)This method is used for adsorption, partition, ion exchange chromatography as there is wide range of adsorbents available.
7)The individual samples do not get diffused as compared to paper chromatography hence sensitivity of detection is more.
8)The components which are separated can be recovered easily by scratching the powdery coating of plate and quantitative separation of spots or zone are possible.
9)It is possible to visualize the components for identification by UV light as the inorganic adsorbent background does not floresce.
10)This method can be applied to preparative separation with the help of thicker layers of adsorbents.