not mock (chromatography)

• which technique is used to separate amino acids

  thin layer chromatography (TLC)
• how do the molecules separate in TCL

  how long they spend in the different phases

  according to size/ charge - smaller molecules move faster
• what is the stationary phase

  a thin layer of solid e.g. silica gel on a sheet of plastic or glass
• Why is TLC better than paper chromatography?

  it's quicker, produces a clearer separation and can be used for a wider range of chemicals
• How can amino acids be identified?

  using the reference samples (known amino acids)
• how can invisible spots be viewed on the chromatogram

  using a UV lamp and then marking them
• equation for Rf value

  distance moved by spot/distance moved by solvent
• what type of analysis are paper and TLC

  qualitative - they don't show how much chemical is present - only what is or isn't present
• how can paper and TLC be used for quantitative analysis

  - they give a rough idea on the concentration based on how intense the colour is

  - spots can be removed and processed to find an amount
• steps for paper chromatography?

  draw a pencil line 2cm from the bottom of the paper and put spots of amino acids on the line

  2. add 1cm³ of the solvent to a beaker and dip the bottom of the paper into it this should be done in a fume cupboard

  3. cover with a lid to prevent evaporation

  4. spray the paper with ninhydrin solution to make the amino acids visible

  5. calculate the Rf value