Thin layer chromatography

Thin layer chromatography (TLC) is similar to paper chromatography but instead of paper, the stationary phase is a thin layer of an inert substance (eg silica) supported on a flat, unreactive surface (eg a glass plate).

TLC has some advantages over paper chromatography. For example:

  • the mobile phase moves more quickly through the stationary phase
  • the mobile phase moves more evenly through the stationary phase
  • there is a range of absorbencies for the stationary phase

TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the components in the mixture - and are therefore easier to analyse.

The distance a sample travels can depend on the size or the polarity of the molecules involved. Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile.

Likewise, the polarity of the molecules can affect how far the spots travel, depending on the type of solvent used. Polar molecules will be more strongly attracted to polar solvents, and so would move further if a polar solvent was used as opposed to a non-polar solvent.

The distance that spots move can be compared to the overall distance the solvent has moved and comparisons and measurements made.

A chromatogram showing a substance has travelled 3 cm from the baseline. The solvent front is at 6 cm, so the solvent has travelled 6 cm.