anyalysis

Question 1

What are the 2 phases in chromatography

Answer 1

• Stationary phase - the solid on solid support (as in TLC) or liquid on solid support (as in GC).
• Mobile phase - liquid (as in TLC) or gas (as in GC).

Question 2

How does adsorption and solubility affect chromatography? (include polarity)

Answer 2

1. Adsorption:
   a. Mobile phase interacts with surface of stationary
   phase by adsorption.
   b. More adsorption ⇒ more interaction ⇒ travels
   slower / less distance.
2. Solubility:
   a. If mobile phase is nonpolar and stationary phase is polar ⇒ less soluble ⇒ passes quicker.

Question 3

How to calculate Rf and therefore the substance in the tlc

Answer 3

• Distance moved by compound / distance moved by solvent. • By comparing to database values.

Question 4

What problems are there with TLC and GC? Why?

Answer 4

Some substances won’t separate since they have similar retention factors / retention times ∵ they’re structurally similar.
It is often used alongside mass spectroscopy.

Question 5

What 3 factors affect retention TIMES? And why?

Answer 5

1. Solubility - more soluble compounds will take longer to move via the tube.
2. Boiling point - a substance with a high boiling point will spend more time condensed as a liquid than a gas (taking longer).
3. Temperature of gas chromatography instrument - high means more evaporated as gas so move quickly.

Question 6

Describe the setup of gas chromatography (GC)

Answer 6

● Mobile phase is a mixture of gas.
● Stationary phase is high b.p. liquid coating the column. ●
●
Time taken to pass via column / retention time is used to identify substance.
Area under each peak is proportional to amount of substance (called peak integration value).

Question 7

What is a calibration curve?

Answer 7

A curve
relating peak areas to concentrations.

Question 8

How is a calibration curve set
up?

Answer 8

Prepare several standard solutions of known concentrations. Obtain gas chromatograms for each standard solution.
Plot a calibration curve of peak area against concentration.

Question 9

What does a liquid stationary phase separate
organic compounds by?

Answer 9

by relative solubility