Separation by chromatography 76-77 Flashcards
Why is chromatography a very useful method of analysis?
It has the ability to separate out components with similar physical properties in very complex mixtures.
Only small samples are required and after separation, the pure components can be analysed precisely.
What is chromatography used in the analysis of?
Used in the analysis of drugs, plastics, flavourings, foods, pesticides, forensic evidence, fuels, air samples, water samples.
Explain how chromatography works.
A line is drawn on a chromatography plate and a sample is placed on the line. The plate is placed in a tank of the solvent, the line drawn is above the height of the solvent. The setup is left till the solvent has reached near the top of the plate. The solvent in the plate is allowed to dry and evaporate and then is analysed.
What does the mobile phase do an and what does the stationary phase do?
- The stationary phase is fixed in place
- The mobile phase moves in a definite direction.
Explain how chromatography leads to the separation of different components in the mixture.
The stationary phase interacts with the components in the mixture, slowing them down. The greater the interaction, the more the components are slowed down.
- This allows different components to flow over the stationary phase at different speeds, separating the components.
What is the stationary phase and mobile phase in thin-layer chromatography?
The stationary phase is a solid, and the mobile phase is a liquid.
What is the stationary phase and mobile phase in gas chromatography?
In gas chromatography the stationary phase is liquid or solid on a solid support, and the mobile phase is a gas.
Efficient separation depends on what two factors?
A solid stationary phase separates by adsorption. As the mobil phase passes over the stationary phase, component molecules are able to bind to the solid making up the stationary phase. This happens at the surface of the stationary phase.
How does a liquid stationary phase separate components?
A liquid stationary phase separates by relative solubility. Some components dissolve more readily in the liquid and these are slowed down more than components with lower solubility.
