Lab 4: Amino Acid Detection Flashcards
What is a stationary phase in chromatography?
Solid and/or a liquid supported on a solid
What is a mobile phase in chromatography?
- A liquid or gas
- The mobile phase flows through the stationary phase and carries the components of the mixture or chemical with it
In paper chromatography, should the solvent level be above or below the line with the spots (amino acids)?
BELOW
Why do we cover the container in paper chromatography?
- To make sure that the atmosphere in the beaker is saturated with solvent vapour
- Stops the solvent from evaporating as it rises up the paper
What happens when the solvent has migrated almost to the end?
The paper is dried and sprayed by ninhydrin solution
What is the purpose of the ninhydrin solution spray?
At 100oC, ninhydrin reacts with a-amino acids to form a purple colour, allowing the amino acids to be visualized
What is the unit of the Rf value?
None
How do you calculate the Rf value?
Distance of the spot on the TLC-plate/Distance of the solvent front
Where should you measure the amino acids spots?
In the middle of the coloured spots
How many times were the amino acids spotted? What about the unknowns?
- Amino acids: 3x
- Unknown: 6x
What is the stationary phase in paper chromatography?
White, uniform, absorbent chromatography paper, composed of cellulose fibers and water
Why do we use cellulose in paper chromatography?
The OH- groups can absorb H2O vapor, rendering the stationary phase polar
What is the polarity of the stationary phase?
Polar
What is the polarity of the mobile phase?
Non-polar
What is the mobile phase in paper chromatography?
Non-polar solvent (72% organic solution, 20% diluted H2O, 8% acetic acid)
What controls the distance at which amino acids travel?
- The solvent carries the mixtures up the paper by capillary action
- The interactions of the compounds with the non-polar solvent and polar paper control the distance at which they travel
What do polar amino acids display in paper chromatography? How is the distance at which it travels? How is the Rf value?
- Adsorption and attraction in the polar paper
- Low solubility in the non-polar solvent
- Low distance
- Low Rf value
What do non-polar amino acids display in paper chromatography? How is the distance at which it travels? How is the Rf value?
- Low adsorption to the polar paper
- High solubility in the non-polar solvent
- Long distance
- High Rf value
Is phenylalanine polar or non-polar? Why?
- Non-polar
- Hydrophobic aromatic side chain (benzene ring), composed solely of Cs and Hs, justifies its non-polar nature
Are charged amino acids polar or non-polar? Why?
- Polar
- Due to a separation in electrical charge, creating a dipole moment, allowing them to form hydrogen bonds with the polar paper
Is lysine polar or non-polar? Why?
- Polar
- Contains a second primary amino group, creating a positive (basic) charge
Are aspartic acid and glutamic acid polar or non-polar? Why?
- Polar
- Both have a second carboxyl group, creating a negative (acidic) charge
Why does glutamic acid travel farther up the paper than aspartic acid?
Since glutamic acid has a longer carbon chain, which decreases its polarity
Why is Diet Pepsi composed of? What does that make?
- Phenylalanine and aspartic acid
- Aspartame (methyl ester of the amino acids linked through a peptide bond)
How does aspartame compare to sucrose?
It is 200 times sweeter than sucrose
What are the 9 essential amino acids?
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
What are the 6 conditional amino acids?
- Arginine
- Cysteine
- Glutamine
- Glycine
- Proline
- Tyrosine
