Chromatography

Question 1

Outline the steps needed to locate the positions of amino acids on a TLC plate and calculate their Rf values

Answer 1

-Use UV
-measure the distance from the initial pencil line to the spots (x)
-measure the distance from the initial pencil line to the solvent front line (y)
-Rf = x/y

Question 2

Why do amino acids have different Rf values?

Answer 2

-they have different polarities
-therefore they have different retention values in the stationary phase

Question 3

Why was propanone present in samples of the eluent collected first, whereas samples containing propan-2-ol were collected later?

Answer 3

propanone less polar
-propan-2-ol has greater affinity for stationary phase

Question 4

Outline how chromatography is able to separate a mixture of compounds

Answer 4

-solvent is mobile
-stationary phase / AL / silica
-amino acids travel at different speeds

Question 5

Outline how chromatography is used to separate and identify ETU from a sample of Zineb powder

Answer 5

-Zineb mixed with solvent
-use TLC/paper
-ETU travels furthest on paper/TLC
-Method of identification of ETU (by comparison with standard using
chromatography)