29 Chromatography

Question 1

What is thin layer chromatography?

Answer 1

• TLC is an analytical technique that indicates how many components are in a mixture.

Question 2

What is the stationary phase in TLC?

Answer 2

A thin layer of a solid adsorbent substance- usually silica.

Question 3

What is adsorption?

Answer 3

• Adsorption is the process by which solid silica holds the different substances in the mixture to its surface.
• The different components in the mixture have different affinities for the adsorbent and bind with differing strengths to its surface.

Question 4

What does Rf stand for?

Answer 4

Retention factor

Question 5

How do you work out Rf value?

Answer 5

(Distance moved by component)/(distance moved by solvent front)

Question 6

What is gas chromatography useful for?

Answer 6

Gas chromatography is useful for separating and identifying volatile organic compounds present in a mixture.

Question 7

What is the stationary phase in gas chromatography?

Answer 7

The stationary phase is a high boiling liquid adsorbed onto an inert solid support.

Question 8

What is the mobile phase in gas chromatography?

Answer 8

The mobile phase is an inert carrier gas such as helium or neon.

Question 9

How are the components in the mixture separated?

Answer 9

• The components of the mixture are separated depending on their solubility in the liquid stationary phase.
• The compounds in the mixture reach the detector at different times depending on their interactions with the stationary phase in the column.

Question 10

What is retention time?

Answer 10

The retention time is the time taken for each component to travel through the column.

Question 11

What information does a gas chromatogram give?

Answer 11

1) Retention times used to be identify components present in sample by comparing it to retention times for known components.
2) Area under graph can be used to determine concentrations of components in sample.