3.3.16 Chromatography - Chemistry Alevel

Description - TLC

A plate coated with a solid and a solvent moves up the plate.

Description - CC

A column is packed with a solid and a solvent moves down the column.

Description - GC

Column is packed with a solid or a solid coated by liquid (liquid absorbed oto a solid), and gas is passed through the column under pressure at high temperature.

What does separation depend on in chromatography?

Separation depends on the balance between solubility in the moving phase and retention by the stationary phase.

How can you identify different substances using chromatography?

Retention times and Rf values are used to identify different substances.

Rf value - calculation

Distance travelled by spot (from centre to pencil line)/distance travelled by solvent (from solvent front to pencil line).

TLC - Why is a lid used?

A sealed system is used to increase the rate of the procedure and to reduce loss of solvent.

TLC - two dots line up what does this mean?

They could contain he same substance or it could just be two different substances with the same solubility/Rf value.

TLC - how to make the spots travel further/separate more

Use a more effective solvent and a longer plate.

TLC - how to visualise spots

Stains or sprays like iodine vapour or ninhydrin. (fluorescent indicator under UV blocked by dots)

TLC - name

Thin layer chromatography

CC - name

Column chromatography

GC - name

Gas chromatography

CC - What is it filled with & why?

Silica or alumina or iron exchange resin granules powder to increase the surface area.

GC - type of column

Capillary glass or metal tube.

GC - examples of carrier gas

It is an inert gas, for example helium, argon or nitrogen, as the components of the mixture are volatile.

GCMS - name

Gas chromatography mass spectrometry

GCMS - description

A sophisticated type of GC where the spirited components are ionised as they emerge from the column and both the identify and quantity are found.