Chromatography Overview

• Chromatography is a separation technique used in forensic science.

Paper Chromatography

• Involves drawing a pencil line on chromatography paper.

• Spots of different food colorings (red, green, blue) are applied on the line.

• Paper (stationary phase) and water (mobile phase) are used for separation.

• Water level must not touch the spots.

• Components separate as water is absorbed.

  • More soluble components travel further.

  • Less soluble components travel shorter distances.

Retention Factor (RF) Value

• Defined as the distance a component travels compared to the solvent distance.

• Larger RF values indicate higher solubility in the solvent.

• Smaller RF values indicate lower solubility.

Thin Layer Chromatography (TLC)

• Similar to paper chromatography but uses a glass plate with a thin layer of absorbent material.

• If components are colorless, ninhydrin may be used to visualize them (turns components purple).

• Chromatograms can also be viewed under UV light.

Applications

• Both chromatography methods are used to identify and compare substances like drugs, inks, lipsticks, saliva, and explosives.

Conclusion

• Paper and thin layer chromatography separate components based on solubility.

• Relative solubility is assessed via RF values: higher RF = more soluble, lower RF = less soluble.