Chromatography Flashcards
What is a phase?
A state of a substance, such as a solid liquid or gas
In chromatography, what is the mobile phase and stationary phase?
Mobile phase- the phase that moves
Stationary phase- the phase that does not move
How does the stationary phase affect the separation. Components in chromatography?
The stationary phase can be solid or liquid
Separation depends on the balance between the solubility of the mobile phase and the retention of the liquid/solid stationary phase
The stronger the retention of the stationary phase, the slower the components move with the mobile phase
What can affect the solubility or retention of a molecule?
Polarity
What are the three types of chromatography?
Thin layer chromatography
Gas chromatography
Column chromatography
What are the uses opf thin layer chromatography?
To check the purity of and to identify compounds
What are the components of thin layer chromatography?
TLC plate (what the components move up)
TCL lid
Liquid solvent
Baseline drawn in pencil
Solvent front
What are the stationary and mobile phases in thin layer chromatography?
Stationary phase- solids ( Al2O3, Si)2) on a glass support
Mobile phases- liquid solvents that move up the TLC plate
Describe how to separate components with thin layer chromatography
Dissolve a small sample of the mixture in the solvent.
Draw the baseline in pencil, at the bottom of the TCL plate.
Add a small spot of the sample on the pencil line and allow it to dry
Place the TCL plate in a beaker containing the solvent- the solvent must be below the pencil line.
Seal the beaker with a lid, allow the solvent to rise up the TCL plate
Once the solvent is almost at the top, remove the plate and mark the solvent front
Use locating agents to make the compounds visible
What are examples of locating agents in thin layer chromatography?
Iodine I2
Ninhydrin AND UV light
What is the equation for Rf values?
Distance moved by the spot/ distance moved by solvent
It is always between 0 and 1
What are limitations of thin layer chromatography?
Similar compounds have similar Rf values
If a compound is unknown, there is no data to find it
Solvents are difficult to set right
What are the uses of column chromatography?
To separate and collect large volumes or components
What are the stationary and mobile phases in column chromatography?
Stationary phase- solid Al2O3, SiO2 (powder)
Mobile phase- a liquid solvents called the eluent
What is an eluent?
A liquid mobile phase in column chromatography
Describe how to set up and carry out column chromatography
Fill a glass tube with the stationary phase, it is held in place by a filter. The tap at the bottom is closed
Cover the powder in the solvent (the mobile phase)
Dissolve the sample in the minimum amount of solvent, and place it on top of the stationary phase.
Open the tap so the mixture can run through the column- continue to add solvent at the top
The time taken for each component to reach the end of the column is recorded. This is known as the retention time
What is the retention time in column chromatography?
The time taken for the components to each reach the end of the column
What is gas chromatography and what is it used for?
It is a very sensitive quantitative method
Used to separate volatile liquids
What are the stationary and mobile phases in gas chromatography?
Stationary- thin layer of liquid or solid coating the inside of the column
Mobile- an inert gas (He, N2) that moves through the column
What are the components of gas chromatography?
A carrier gas (the mobile phase)
An injector that injects the sample into the chromatograph
A long and coiled column that goes into an oven
The detector
Describe how to carry put gas chromatography?
The mixture is injected into the gas chromatograph, it is vaporised
The carrier gas (mobile phase) flushes the mixture through the long, coiled column
The components slow down as they interact with the stationary phase
Each leaves the column at a different time, and is detected by the detector
The retention time is recorded
What is the retention time in gas chromatography?
The time taken for a component to pass from the column inlet to the detector
What does a longer retention time indicate?
The component has a high retention by the stationary phase, and is less soluble in its moving phase
What does a shorter retention time indicate?
The component is retained less by the stationary phase, and is more soluble in the mobile phase
