Purity Testing
1. TLC Plate Illustration
A TLC (Thin Layer Chromatography) plate is used to separate components of a mixture. It
consists of a stationary phase (usually silica gel) coated on a glass or plastic sheet. A sample is
applied as a small spot at the baseline, and the mobile phase rises through capillary action.
Typical TLC plate regions:
I.​ - Baseline: Where the sample is spotted
II.​ - Solvent front: Final position of the solvent
III.​ - Separated spots: Indicate different components
If a substance is pure, it usually shows only one spot on the TLC plate (under UV light
or using a staining reagent).
2. Single vs Multiple Spots
TLC is a quick method to check purity:
- Single Spot: Indicates the substance is likely pure, as only one component is
present. - Multiple Spots: Indicates impurities or a mixture of compounds.
The Rf value (distance traveled by the compound / distance traveled by solvent) is also
compared with a known standard to help verify the identity of the compound.
3. Confirmation Using IR and NMR
While TLC gives quick separation information, final confirmation of purity and identity is
done using spectroscopic methods:
IR Spectroscopy:
I.​ - Identifies functional groups
II.​ - A pure compound shows clean, characteristic absorption peaks
NMR Spectroscopy:
I.​ - Gives detailed structural information
II.​ - A pure compound shows well-resolved peaks without unexpected signals
Together, TLC, IR, and NMR provide a complete analysis of purity in organic compounds.