Chromatography: Amino Acids

Question 1

Chromatography is a technique that can be used to

Answer 1

separate a mixture into its individual components

Question 2

Chromatography relies on

Answer 2

the differences in the solubility of the different chemicals (called ‘solutes’) within a mixture

Question 3

All chromatography techniques use two phases:

Answer 3

The components in the mixture separate as the mobile phase travels over the stationary phase

Differences in the solubility of each component in the mobile phase which affects how far each component can travel

Those components with higher solubility will travel further than the others

This is because they spend more time in the mobile phase and are thus carried further up the paper than the less soluble components

Question 4

Paper chromatography is one specific form of chromatography
In paper chromatography:
The mobile phase is the ……

The stationary phase in

Answer 4

The mobile phase is the solvent in which the sample molecules can move, which in paper chromatography is a liquid e.g. water or ethanol

The stationary phase in paper chromatography is the chromatography paper
Paper chromatography method

Question 5

Paper chromatography can be used to separate a mixture of amino acids how is this done first step

Answer 5

A spot of the unknown amino acid sample mixture is placed on a line at the bottom of the chromatography paper

Question 6

2nd after putting A spot of the unknown amino acid sample mixture is placed on a line at the bottom of the chromatography paper

what do you put next to it on the chromatography paper to compare

Answer 6

Spots of known standard solutions of different amino acids are then placed on the line beside the unknown sample spot

Question 7

3rd step
The chromatography paper is then ………… in a solvent

Answer 7

suspended

Question 8

Each amino acid will be more or less soluble in the mobile phase than others and will therefore separate out of the mixture travelling with the solvent at different times/distances from the line, depending on their ….

Answer 8

Charge

Size

Question 9

The unknown amino acid(s) can then be identified by

Answer 9

by comparing and matching them with the chromatograms of the known standard solutions of different amino acids

If a spot from the amino acid sample mixture is at the same distance from the line as a spot from one the known standard solutions, then the mixture must contain this amino acid

Question 9

In order to view the spots from the different amino acids, it may be necessary to

Answer 9

first dry the chromatography paper and then spray it with ninhydrin solution (this chemical reacts with amino acids, producing an easily visible blue-violet colour)

Question 10

Exam Tip
It is always worth trying to understand why a certain practical technique is useful.

An example of when chromatography would be used is if you have an unknown liquid and you have determined it contains protein using a Biuret test.

Chromatography will then show you which……..

Answer 10

amino acids are present so you can better understand the potential use or function of the sample. This could be useful in crime scene investigations or in detecting additives or spoilage in foods.