chromatography Flashcards
How does gas chromatography (GC) separate the compounds in the mixture?
(Relative) solubility (in stationary phase)
What does your answer to (b)(i) suggest about the interaction of this compound with the phases present in the column?
Compound (B) is less soluble in the stationary phase/ liquid
Explain how GC–MS enables the products to be identified.
idea of separating (the components/compounds)
AND idea of (identifying compounds by) comparison with a
(spectral) database
Name the process by which TLC separates amino acids.
Adsorption
How could the chemist use the results from GC to predict the number of esters in the mixture and their relative proportions?
(number of esters) from number of peaks/retention times
AND
(proportions) from (relative) peak areas
Why would there be some uncertainty about using GC alone to predict the number of esters in a mixture?
(Some esters may have) same retention time
How does a liquid stationary phase separate the organic compounds in a mixture?
(relative) solubility
Suggest how well these four compounds would be separated using the alkane stationary phase. In your answer, include some indication of the length of the retention times.Explain your answer.
The esters would have similar retention times
AND
similar structures/molecules OR same functional groups
OR similar polarities OR similar solubilities
Alcohol would have short retention time
AND
alkane would have long retention time
Compounds in the smoke from forest fires can be analysed using GC-MS.
Explain how GC-MS enables the compounds to be identified.
idea of separating (the components/compounds)
idea of (identifying compounds) by comparison with a
(spectral) database
Explain how TLC separates compounds in the mixture.
Adsorption (onto the stationary phase)
State what is meant by retention time.
The time (from the injection of the sample) for the component to
leave the column
Explain the possible limitations of GC in separating the two esters.
They have similar retention times
Name the process by which TLC separates α-amino acids.
adsorption
The chromatogram was treated to show the positions of the separated α-amino acids.Explain how the student could analyse the chromatogram to identify the three α-amino acids that were present.
measure how far each spot travels relative to the solvent front or
calculate the Rf value
compare Rf values to those for known amino acids
Several α-amino acids have structures that are very similar.Suggest why this could cause problems when using TLC to analyse mixtures of α-amino acids.
(amino acids won't separate because) similar compounds have similar Rf (values)
