Chromatography. Flashcards
What is the definition of “stationary phase”?
In chromatography the part that does not move.
What is the definition of “mobile phase”?
In chromatography it is the part that moves.
What is the stationary phase in gas chromatography?
Silica or alumina powder.
What is the mobile phase in gas chromatography?
An unreactive carrier gas such as nitrogen.
How do you calculate the Rf value?
Distance travelled by substance divided by distance travelled by solvent.
What is the mobile phase in TLC and paper chromatography?
The solvent.
What is the stationary phases in TLC and paper chromatography?
TLC- The plate.
Paper- The paper.
Define “phase”.
A substance in a liquid/solid/gas state.
Describe the steps needed to carry out Gas Chromatography.
1) The sample is turned into the gas state when injected into the column.
2) The carrier gas (nitrogen) pushes the sample through the column.
3) The different components take different amounts of time to travel through the column, depending on how strongly they bond to the stationary phase.
4) A detector sends signals to a component as each computer leaves the column, and produces a chromatogram in which each component equals a peak plotted against time.
Describe the steps needed to carry out Paper Chromatography.
1) Draw a baseline in pencil and add a dot of ink.
2) Add a shallow amount of a solvent (e.g. ethanol/water) to a beaker.
3) Add the paper to the beaker, taking care to ensure the baseline is not submerged in the solvent.
4) A lid may be added to prevent solvent evaporation.
5) The solvent may be left to travel up the paper, carrying along the components of the ink with it.
6) Remove the paper from the beaker before the solvent reaches the top.
Describe the steps needed to carry out TLC.
1) Put the solvent into a chromatography tank to a depth of about
1 cm (Figure 2). If the solvent is flammable, make sure that there are no naked flames, and that the room is well ventilated.
2) Add a small amount of the sample to the baseline, taking care not to damage the powder on the plate.
3) Let the solvent travel through the powder, and take the plate out before it reaches the top.
4) Analyse the pattern of coloured spots, which is called a chromatogram.
Why can’t oxygen be used in Gas Chromatography?
It varies for the gas chromatograph used, but in general the gas must be chemically inert, dry, and free of oxygen. These conditions are required because otherwise the carrier gas might chemically react and interfere with the surface of the gas chromatograph or the gases being studied.
Define Chromatography.
Chromatography is a technique used to separate soluble substances that have been mixed together.
Why is Chromatography successful?
Because different substances have different solubilities.
Why is the baseline in Chromatography drawn in pencil?
The ink may get separated in the experiment and interfere with the results).
