CAIE A-Level Chemistry 37.2.1 Gas–Liquid Chromatography Terms

Practise defining retention time and choosing the mobile and stationary phases used in gas–liquid chromatography.

Exam points

state that the mobile phase is an unreactive carrier gas moving the vaporised sample through the column
state that the stationary phase is a high-boiling non-polar liquid held on a solid support
define retention time as the interval between injecting a component and detecting it after the column

[Maximum number: 2]

Lactic acid, $\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{COOH}$ , is the only monomer needed to form the polymer polylactic acid, PLA.

(a)

An impure sample of $\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{COOH}$ contains pentan-3-one as the only contaminant. The mixture is analysed using gas/liquid chromatography. The pentan-3-one is found to have a longer retention time than the lactic acid.

[ 2 ]

(i)

Explain what is meant by retention time.

[ 1 ]

(ii)

Suggest suitable substances, or types of substances, that could be used as the mobile and stationary phases.
mobile phase
stationary phase

[ 1 ]

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37.2.1—And understand the terms question 1

Question (a)

Question (i)

Question (ii)