Question | Answer |
Mobile phase | phase that moves in chromotography |
Stationary phase | phases that does not move in chromotography |
Rf | distance moved by component divided by distance moved by solvent form |
Principles behind chromotography | different components have different affinties, for SP and MP |
What does the stationary phase do? | interacts with components, slowing them down. |
Adsorption | solid SP, components attach to surface. Stronger the absorption the slower the components |
Relative Solubiltiy | liquid SP, components dissolve in solvent, greater the solubility the more the molecules are slowed down. |
TLC SP is | silica gel or alumina |
TLC MP is | liquid solvent |
Why is TLC placed in a sealed container | allow solvent vapours to saturate paper, and prevent solvent loss |
What is used to make colourless compounds visible? | UV light or locating agent. |
Limitations of TLC | similar solvents with similar Rf values, unknown compounds have no Rf reference, difficult to find a solvent that will separate all compounds. |
GC | Capillary column, detector, recorder, oven, column inlet, gas supply |
GC SP | silicone polymers, long chained alkanes with high boiling points |
GC MP | carrier gas eg nitrogen/helium |
Why are different components slowed down? | By different amounts. |
How to improve separation | different oven temperatures, different flow rates |
Limitations | similar chemicals have similar retention times, not all substances will be separated and detected, unknown compounds will have unknown retention times. |
How to increase reliability | check GC of sample against reference containing suspected sample |
Uses of GCMS | forensics, airports, environment, space probes. |