1.11 Interpreting chromatography experiments

The single spot of the mixture, placed on the  baseline at the start of the experiment, gets separated into a series of spots arranged vertically up the chromatography paper.  This is called a chromatogram.

Each spot in the chromatogram is a different substance from the mixture (although sometime spots can be overlapping, if to substances in the mixture have the same or very similar solubility).

If spots are the same colour and have moved the same distance then they are likely to be the same substance.

Example:

chromatogram1

In the experiment shown above,  an unknown mixture has been spotted on the baseline (to the left) and then spots of three pure substances, A, B, and C that are thought may be in this mixture have been spotted alongside the unknown.  The chromatogram has then been produced by allowing a solvent to soak up from the bottom of the paper.

When we interpret the results fully we can make the following statements:

  • The unknown contains (at least) three components in the mixture (because there are three spots above where the unknown started).
  • The unknown contains pure substance A (because the spot from A has travelled the same distance from the baseline and is the same colour as the blue spot in the unknown).
  • The unknown does not contain pure substance B (because there is no spot from the unknown that is green or has travelled the same distance from the baseline as the spot from B).
  • The unknown contains pure substance C (because the spot from C has travelled the same distance from the baseline and is the same colour as the orange spot in the unknown).
  • There is another substance in the unknown that is not A, B or C, which we have not yet identified. We may need to run experiments with some more pure substances to find a match that will allow us to identify this component.