Activity 4: Thin Layer Chromatography

Question 1

chromatography

Answer 1

• a class of techniques used to separate components of a mixture based on physical property differences

Question 2

How are the components of a mixture separated?

Answer 2

• based on the partitioning of molecules between two phases (stationary phase and mobile phase)
• governed by polarity, size, volatility

Question 3

What is a stationary phase?

Answer 3

• solid phase in the case of TLC and column chromatography, liquid in gas chromatography
• stationary phase does not move, molecules move through the stationary phase
• mostly composed of silica
• when the stationary phase is polar, this is referred to as normal phase chromatography

Question 4

reverse phase chromatography

Answer 4

• nonpolar stationary phase
• modified silica in which the hydroxy groups are functionalized with long C18 gains

Question 5

mobile phase

Answer 5

• solvent in the case of TLC and CC; gas phase in the case of GC
• can be a pure solvent or a mixture of solvents
• mobile phase moves through the stationary phase via capillary action

Question 6

partition coefficient, Kp

Answer 6

• defines the degree of separation of the analytes
• [X]stationary phase/[X]mobile phase
• high Kp = higher retention = moves slower = more polar
• low Kp = lower retention = moves faster = less polar

Question 7

uses of TLC

Answer 7

• assess sample purity
• assess molecular polarity
• establish compound identity
• monitor reaction progress
• monitor CC separations
  qualitative analysis

Question 8

What is the stationary phase made from?

Answer 8

• thin layer of silica coated onto a solid support (plastic, glass, metal)

Question 9

general set-up

Answer 9

• mobile phase solvent (eluent)
• filter paper: saturates the environment with the solvent
• lid
• TLC plate

Question 10

retention factor

Answer 10

• affinity of a compound for the stationary phase
• Rf = distance spot traveled/distance solvent traveled
• high Rf = low Kp = less polar
• low Rf = high Kp = more polar

Question 11

identify compound

Answer 11

• different Rf = different molecules
• same Rf = possibly the same molecules

Question 12

assess sample purity

Answer 12

• multiple spots = impure
• one spot = pure (or improper solvent which causes lack of separation)