Instrumental Analysis - Separation techniques

Instrumental Analysis - Separation techniques

1. Gas chromatography

   • Very sensitive, very fast, very accurate
   • Different components of the gas move at different rates through the column and they separate
     • Mass spectrum
     • Gas chromatograph (Rt graph)
   • Method
     • Sample gas is vaporised and is passed through coiled column [oven] (carried by a gas)
       • The components of the gas move at different speeds and get recorded as peaks on a chart by a detector
         • Retention time graph
           • GC-MS
             • Attach to mass spectrometer
               • Mass spectrum ( = pattern of peaks)
                 • Can get molecular mass of each compound from their molecular ion peaks (last peak on right)
                   • Compare results from computer database to see what compound it is
           • Rt = time spent in column
     • Uses coiled column
   • 'Carrier' gas carries the sample gas

2. Paper chromatography

   • Used to separate mixtures of a compound
     • To identify food additives
       • To ensure they meet legal safety standards
   • Method
     • Put spot of mixture above pencil line on bottom of paper and place in solvent upright
       • Solvent moves up the paper carrying the mixture
         • The components of the mixture separate out - different colours
     • Uses chromatography paper
   • Different components of the mixture move at different rates up the paper and they separate
     • Rf = distance moved by component / distance moved by solvent
       • Higher the Rf value, more soluble it is (and vice versa)
         • The coloured paper is called the chromatogram
     • Chromatogram
   • Solvent carries the components - keep lid on so it doesn't evaporate