Chromatography

• Chromatography involves passing a mixture dissolved in a mobile phase (a solvent) through a stationary phase (e.g. chromatography paper), which separates the molecules according to their specific characteristics (e.g. size/charge).
• In thin-layer chromatography, such as the separation of photosynthetic pigments, the stationary phase is a thin layer of absorbent material (e.g. silica gel or cellulose) attached to a solid plate. A sample is placed near the bottom of the plate which is placed in an appropriate mobile phase (solvent).
• Rf value equation:

  Distance Travelled By The Spot (x) ÷ Distance Travelled By The Solvent (y)
• Rf values are useful because they can be compared with Rf values from known samples or standards to provide objective and accurate results.
• Paper chromatography method:

  1. a pencil line is drawn and a spot of mixture is placed here and left to dry
  2. the paper is suspended in a solvent (mobile phase) just below the pencil line
  3. as the solvent travels upwards the components of the mixture move with it at different speeds
  4. produces a chromatogram