Page 129 - phytochemistry general program

(b) Determination of complexity of mixtures: TLC provides a picture about the .2
number, nature and relative concentrations of mixture components. It is also a
valuable tool for the characterization of very complex natural products. For many
purposes, an exact knowledge of the identity or quality of the constituents of such
mixtures is not required. Instead, the chromatographic pattern (i.e. number, shape,
colors, and relative positions of the spots of these products form after
chromatography) may suffice for their characterization and identification (quality

control).

(c) Determination of the purity of materials: TLC is a very sensitive analytical tool.
As a rule, the material is considered pure when no additional spots are illustrated

after spotting certain amount of the material.

(d) Monitoring the progress of chemical reations: TLC can be used to monitor the
progress of chemical reactions. Periodical TLC investigation of the reaction
mixture many help indicating the progress of the chemical reaction. The

disappearance of the starting materials indicates the completion of the reaction.

Preparative TLC

Thin-layer chromatography can be adopted for the isolation of milligram or gram
quantities of pure materials. The technique is ideally suitable for the fractionation
of materials with, properties that prohibit handling of large amounts, such as
radioactive and toxic substances. It is sometimes also used for the isolation of
natural products from complex mixtures. Adsorption TLC is almost the only

preparative technique used.

Sample band Pilot
spot

Fig. 12: Preparative TLC Procedure:

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