Paper Chromatography
Watch pigments migrate and separate in real time. Measure Rf values, explore solvent polarity effects, and identify unknown compounds — all in a high-fidelity virtual laboratory environment.
| Pigment | Color | Rf |
|---|---|---|
| Start simulation to see Rf values | ||
| # | Sample | Solvent | Polarity | Paper (cm) | Pigment | Spot Dist (cm) | Solvent Dist (cm) | Rf Value | Identity |
|---|---|---|---|---|---|---|---|---|---|
| No observations recorded yet. Run experiment and press "+ Record". | |||||||||
Principle of Paper Chromatography
Paper chromatography is a separation technique based on the differential migration of components in a mixture across a stationary phase (cellulose paper) by a mobile phase (solvent).
Components partition between the two phases according to their relative solubility — polar compounds are retained more strongly by the polar paper; non-polar compounds travel further with the solvent.
Rf values are dimensionless, between 0 and 1, and characteristic of a compound under defined conditions.
The Rf Value — Retention Factor
The Rf (Retardation Factor or Retention Factor) is the fundamental quantitative measurement in chromatography.
- Rf = 0: compound stays at baseline (strongly retained)
- Rf = 1: compound moves with solvent front (not retained)
- Higher polarity compound → lower Rf in polar solvent
- Same compound, same conditions → same Rf always
- Rf is used to identify and compare compounds
Rf is reproducible only when temperature, solvent saturation, paper type, and technique are kept constant.
Solvent Polarity & Separation
The choice of solvent is critical. The principle of "like dissolves like" governs how well each pigment is carried by the solvent.
- Polar solvents (water, ethanol) carry polar compounds higher
- Non-polar solvents (petroleum ether) carry non-polar compounds higher
- Mixed solvents give intermediate separation profiles
- Solvent polarity directly determines Rf values
- Changing solvent changes all Rf values simultaneously
For plant pigments, petroleum ether separates carotenes best; ethanol separates chlorophylls and xanthophylls.
Plant Pigments — Spinach Extract
Spinach leaf extract contains multiple photosynthetic pigments that separate beautifully on paper chromatography:
- β-Carotene (orange): Rf ≈ 0.95 — most non-polar, travels furthest
- Xanthophyll (yellow): Rf ≈ 0.71 — moderately polar
- Chlorophyll a (blue-green): Rf ≈ 0.65 — polar
- Chlorophyll b (yellow-green): Rf ≈ 0.45 — most polar, stays lowest
The separation of these pigments demonstrates the broad range of Rf values achievable and their correlation with molecular polarity.
Sources of Experimental Error
- Dipping paper too deep — baseline immersed in solvent
- Allowing solvent to reach the top — Rf becomes inaccurate
- Spotting too much sample — spots streak and overlap
- Uneven paper surface — causes band distortion
- Temperature variation — alters solvent viscosity and Rf
- Measuring before spot is fully dried — inaccurate distances
Always pencil the baseline before applying sample and mark the solvent front immediately when development is complete.
Applications of Chromatography
- Food dye identification and quality control
- Pharmaceutical purity testing
- Forensic analysis (ink, drugs, explosives)
- Environmental pollutant detection
- Biochemical research (amino acids, proteins)
- Plant pigment analysis and ecology
- Clinical diagnostics (blood components)
Paper chromatography is the foundation of more advanced techniques like HPLC, GC, and mass spectrometry-coupled chromatography used in modern analytical labs.