Chromatography

Question 1

How do stationary phases differ in separation?

Answer 1

• Solid stationary phase separates by adsorption.

* Liquid stationary phase separates by relative solubility.

Question 2

Thin- Layer Chromatography

Answer 2

• Separates components by adsorption.
• Solid stationary- silica gel. Mobile phase- solvent, eg: ethanol.
• How far a component travels depends on how strongly attracted it is to the stationary phase. a substance that’s strongly absorbed will move slowly and won’t travel as far as one that’s weakly absorbed.
• The stationary phase and solvent used will affect the Rf value.

Question 3

Gas Chromatography:

Answer 3

• Mobile phase: unreactive carrier gas- N2, He.
• Stationary phase: viscous liquid on an inert solid- oil.
• Retention time: time taken for a compound to travel from the point of injection to the detector. This can be used to identify substances.
• A substance with a high solubility will spend more time dissolved, so it will take longer to travel through the tube to the detector.

Question 4

How does GC Chromatograms show proportion of the components in a mixture?

Answer 4

•The area under each peak is proportional to the amount of substance.

Question 5

What are the limitations of gas chromatography?

Answer 5

• Similar compounds will often have similar retention times.
• Unknown compounds have no reference retention times for comparison.
• Retention times can vary as they are dependent on temperature, pressure, gas and individual machine.

Question 6

What happens when mass spectroscopy is combined with chromatography?

Answer 6

• Provide a powerful analytic tool than chromatography alone.
• To generate mass spectra which can be analysed or compared with a spectral database by computer for a +ve identification of a component.
• Eg: GC-MS can be used in analysis in forensics, environmental analysis; airport security, space probes.

Question 7

What is chromatography?

Answer 7

• Is an analytical technique that separates components in a mixture between a mobile phase and a stationary phase.
• Mobile phase: gas or liquid.
• Stationary phase: solid (TLC) or liquid or solid on a solid support(GC).