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Paper chromatography theory and practice

Chemical analysis • Purity, formulations, and chromatography

Key concepts

What you'll likely be quizzed about

  • Paper chromatography is a technique using paper as the stationary phase and a liquid solvent as the mobile phase.
  • A mixture spot is applied to a pencil-drawn baseline, and the solvent moves up the paper by capillary action.
  • Different components travel at different rates, creating separate spots and forming a chromatogram.
  • Separation occurs because of each component's solubility in the mobile phase and adhesion to the stationary phase.
  • Components that dissolve better in the solvent migrate further; those adhering to the paper migrate less.

Flashcards

Test your knowledge with interactive flashcards

What is the formula for Rf value?

Click to reveal answer

Rf = distance travelled by substance ÷ distance travelled by solvent front.

Key notes

Important points to keep in mind

Always draw the baseline in pencil to avoid running ink.

Spot volumes must be small to prevent spreading and tailing.

Measure distances from the baseline to the centre of spots and to the solvent front.

Mark the solvent front immediately after removing the paper to avoid evaporation errors.

Run standards under identical conditions for reliable identification.

Keep solvent depth below the baseline so spots do not dissolve directly into the solvent.

Use an appropriate solvent polarity to maximize separation of target substances.

Control temperature and humidity to enhance reproducibility.

Use locating reagents or UV light for invisible compounds.

Report Rf values as unitless numbers with experimental conditions noted.

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