Chemistry - Rings, Polymers and Analysis - F324 - Separation by Chromatography (3) Flashcards
What is the advantage of chromatography?
Chromatography can separate out components with similar physical properties in very complex mixtures.
Define a phase in chromatography?
A phase is a physically distinctive form of a substance, such as the solid, liquid and gaseous states of ordinary matter.
Define the mobile phase.
The mobile phase is the phase that moves in chromatography.
Define the stationary phase.
The stationary phase is the phase that does not move in chromatography.
On which basis does chromatography work?
Chromatography works on the basis that different components have different affinities for a stationary phase and for a mobile phase.
What is the stationary phase in thin layer chromatography?
In thin layer chromatography, the stationary phase is a solid.
What is the mobile phase in thin layer chromatography?
In thin layer chromatography, the mobile phase is a liquid.
What is the stationary phase in gas chromatography?
In gas chromatography, the stationary phase is a solid or a liquid mounted on a solid support.
What is the mobile phase in gas chromatography?
The mobile phase in gas chromatography is a gas.
What does a solid stationary phase separate via?
A solid stationary phase separates via adsorption.
What does a liquid stationary phase separate via?
A liquid stationary phase separates via relative solubility.
Define adsorption.
Adsorption is the process by which a solid holds more molecules of a gas or liquid or solute as a thin film on the surface of a solid or, more rarely, a liquid.
What is usually used as the stationary phase of thin layer chromatography?
The stationary phase of TLC is usually a thin layer of an adorbent such as silica gel (SiO2) or alumina (AlO3) coated on a flat, inert support, usually a sheet of glass.
How is the Rf value calculated?
Rf = distance moved by component / distance moved by the solvent front
What are some of the negatives of chromatography?
- similar compounds will have similar Rf values
- unknown compounds have no reference Rf value
- it may be difficult to find a solvent that separates all the components in a mixture
What needs to be considered when choosing a suitable solvent for chromatography?
- if the components are very soluble then they will be washed all the way up the plate
- if the components are not very soluble then there will be very little movement
- trial and error may be necessary to find a suitable solvent.
What type of compounds is gas chromatography most useful for separating?
Gas chromatography is particularly useful for organic compounds that have a low boiling point and evaporate easily
What is the stationary phase in gas chromatography?
The liquid for the stationary phase id often a long chain alkane with a high boiling point. e.g silicone polymers.