CHROMATOGRAPHY (noun)

 

A separation technique using the ability of surfaces to adsorb different substances with different strengths. The mixture to be separated is first dissolved in a suitable solvent, and then a tiny amount (microlitres) of this liquid, no bigger than a spot, is placed onto a chromatographic plate using a capillary pipet (this is known as "spotting" the plate).

The plate is then placed into a chromatographic chamber (beaker) which already contains the solvent that will be used as the carrier phase. The carrier phase then slowly climbs up the plate, and as it does so, it reaches the spot of sample. The carrier phase then picks up the sample and continues to rise up the plate.

As the carrier phase moves along the stationary phase (the plate), the various substances within the sample will adsorb to the stationary phase with different strengths. The substances that adhere the least to the surface move faster and leave behind those that adhere more strongly.

Once the carrier phase has reached the top of the plate, the plate is removed from the chamber and the solvent is allowed to evaporate off the plate. Visual inspection of the plate should reveal several spots at different locations along the plate, with each spot being a different chemical substance from within the original mixture.