Module 6.3.1 - Chromatography and qualitative analysis

• Stationary phase


  The phase that does not move in chromatography-usually a polar solid
• Mobile phase


  The phase that moves in chromatography and is normally a liquid or gas
• Thin Layer Chromatography (TLC)


  A type of chromatography that uses silica gel or alumina on a card as the medium for the stationary phase
• Retention factor (Rf) formula

  distance moved by the component/ distance moved by the solvent front
• The more soluble a solute in the mobile phase ...

  
  

  
  

  
  

  the higher the Rf value or the lower the retention time
• Adsorbent substance


  An agent capable of holding other molecules onto its surface by physical or chemical means. In this case it is usually silica
• Adsorption


  The process of binding or sticking to a surface. It's where the solid silica holds the different substances in the mixture to its surface

  
• Can a component be identified from its Rf / Retention time

  Yes, by matching it with reference Rf/retention times conducted with the same mobile and stationery phases
• Gas Chromatography


  A technique used to separate substances in a gaseous state or volatile compounds (have low boiling points and vapourise easily)

  
• Stationary phase for gas chromatography


  liquid (using relative solubility) or

  solid (using adsorption)
• Mobile phase for gas chromatography

  inert carrier gas e.g. helium or neon
• Retention time


  amount of time a compound spends in stationary phase

  
  

  time for a component to pass from the column inlet to the detector
• The longer a compound is present in the column (longer retention time), the...

  more strongly it is adsorbed o rthe higher the relative solubility

  (interaction between stationary and mobile phases could be either adsorption or relative solubility)
• TLC vs Gas chromatography

  Separates soluble compounds vs volatile compounds

  Solid stationary phase vs Liquid or solid stationary phase

  Solvent mobile phase vs Inert carrier gas mobile phase

  Rf value vs Retention time
• How can you determine the concentration of a sample in gas chromatography


  Peak integrations (or area under each peak)

  
• Procedure of determining the concentration of a sample in gas chromatography (peak integration)

  1) Prepare standard solutions of known concentrations of compound being investigated

  2) obtain gas chromatograms for each solution

  3) plot a calibration curve of relative peak area against concentration

  4) obtain gas chromatogram of compound being investigated (under same conditions)

  5) use calibration curve to measure the concentration of the compound