chromatography

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					   Thin layer chromatography (TLC)

 is a Chromatography technique used to separate mixtures.
Thin layer chromatography is performed on a sheet of glass,
 plastic, or aluminum foil, which is coated with a thin layer
of adsorbent material, usually silica gel, aluminum oxide, or
cellulose (blotter paper. This layer of adsorbent is known as
                     the stationary phase.

After the sample has been applied on the plate, a solvent or
 solvent mixture (known as the mobile phase) is drawn up
  the plate via capillary action. Because different analytes
    ascend the TLC plate at different rates, separation is
                           achieved.
Thin layer chromatography can be used to:
• Monitor the progress of a reaction
• Identify compounds present in a given substance
• Determine the purity of a substance
Thin Layer Chromatography - t.l.c.
                 • Series of spots forms
                 • Compare samples in
                   mixture with known
                   substances.
                 • Measure Rf values.
                 • Coloured compounds
                   & colourless
                   compounds.
Separation and identification.
          Examples on TLC separations

1. Separation of black ink on a TLC
2. The chromatography of an extract
    of green leaves (for example
    spinach)
3. The Chromatogram of
   10 essential oils
   colored with vanillin
   reagent.
                  Preparative TLC

• TLC can also be used on a small semi-preparative scale to
  separate mixtures of up to a few hundred milligrams. The
  mixture is not "spotted" on the TLC plate as dots, but rather
  is applied to the plate as a thin even layer horizontally to
  and just above the solvent level. When developed with
  solvent the compounds separate in horizontal bands

				
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posted:7/22/2012
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