- A baseline is drawn in pencil on the chromatography paper. (Not in ink, as the ink may get separated in the experiment and interfere with the results).
- A small spot of the mixture is placed on the baseline. Sometimes spots of pure substances (reference materials) are put on the baseline too, to allow the colour and height of spots to be compared.
- The bottom edge of the paper is then dipped in a solvent (often water, but many other solvents can be used – we choose whichever solvent separates the mixture most effectively) and left for the solvent to soak up to near the top of the paper.
- The paper is then removed from the solvent, and marked to show where the solvent got up to.
- Rf values are calculated for the spots.
Note: if the solvent is volatile, or hazardous as a vapour, we may arrange the beaker with a lid on the top, so keep the vapour contained. We would also do the experiment in a fume cupboard.