Topic B6: Chromatography
No description yet. This curated deck is ready for daily study.
Card preview (23)
What is TLC (thin layer chromatography) used for?
separating mixture of liquids or solids (dissolved in solvent)
What is the stationary phase of TLC?
solid
What is the mobile phase of TLC?
liquid
What does it mean if one of the components of reaction mixture moves furthest up the TLC plate?
has the strongest affinity for mobile phase, more soluble in the solvent
What is a TLC plate?
piece of plastic/ glass coated with a thin layer of solid (usually silica)
If two of the components are in line with each other it means that…
some of the starting material is still in the reaction mix, hence reaction is incomplete
Why is the baseline drawn in pencil?
stops it interacting with the mobile phase and being brought up the plate (prevents interference with results)
Give 3 ways TLC plat is developed (to make the spots visible)
• UV light • Shake with iodine crystals • Ninhydrin (chemical spray)
How does UV light develop TLC plate?
makes the outline of spots visible, so can be traced with a pencil
How does shaking TLC plate with iodine crystals develop it?
-iodine crystals vaporise -iodine vapour (purple) sticks to spots = visible
How does ninhydrin (chemical spray) develop a TLC plate?
-spray onto chromatogram -ninhydrin reacts with amino acids, resulting in a pink colour
Rf value =
distance moved by spot / distance moved by solvent
What do you place the TLC plate in?
beaker containing a solvent (solvent = mobile phase, moves up TLC plate)
What is gas chromatography used for?
identifying and separating volatile organic compounds
What is the stationary phase of gas chromatography?
(liquid supported on a solid) Column = capillary tube packed with a high BP liquid absorbed onto inert solid support
What is the mobile phase of gas chromatography?
gas -inert so ensures it doesn’t undergo any reactions with organic material e.g. helium
What is retention time?
time taken to travel through column
What does a fast/ small retention time infer?
substance has a higher affinity for the mobile phase
What detects time taken substance to move through column?
detector
What does a high retention time mean?
substance has a stronger affinity for the column, as mix slows down/ is retained for a long duration of time in column (high affinity for stationary phase)
Compare retention times to…
known values to identify substance
What do the peak areas on a chromatograph indicate?
determine concentration of a component greatest area = greatest concentration/ most abundant in sample
How do you determine concentration of one of the substances in a reaction mixture?
use a calibration curve -make standard solutions (of one of the substances) -obtain a chromatograph for every concentration and measure peak area