12 (3.16) Thin-layer chromatography Flashcards
What happens if sample too concentrated?
Spots will overlap
Why dry in fume cupboard?
Solvent is toxic + flammable- so prevents toxic, flammable fumes escaping into room
Why solvent depth below baseline?
If solvent too deep will dissolve sample spots from plate
Why use gloves?
Prevent contamination hands to plate
Why draw pencil line?
will not dissolve in the solvent (if drawn in ink this will dissolve in solvent and run up plate with other components contaminating the plate)
Why UV lamp used?
If spots colourless + not visible
Uses of TLC?
-To separate a mixture into its components for analysis
-allows identification by calculation and comparison of RF values
How to carry out TLC?
- Add solvent to a beaker. Seal to create a saturated environment.
- Draw a pencil line on TLC plate. Spot samples along this line
using a capillary tube. - Add TLC plate to beaker. Make sure solvent is below pencil line.
4.The solvent rises up the TLC plate, bringing components of
the samples with it. - Draw a pencil line where the solvent finishes before it evaporates
- Allow to dry in fume cupboard
How does UV make spots visible?
Many TLC plates have fluorescent dye added to silica or alumina layer that glows when UV light shines on it- make spots appear darker
Can draw circles in pencil around spots
Mobile phase?
Where the molecules can move, always liquid or gas
Ex- solvent
Stationary phase?
Where molecules can’t move
Ex- thin layer of silica or alumina fixed to glass/metal plate
Distance moved by substance depends on?
Depends on its solubility in the mobile phase and it’s retention by the stationary phase
-Differences insolubility and retention buy stationary phase that separate out different substances
