Gas/liquid chromatography
Introduced| English | Meaning |
|---|---|
| carrier gas/ˈkærɪə ɡæs/ | carrier gas |
| retention time/rɪˈtenʃn taɪm/ | The time taken for a substance to pass through a chromatography system and reach the detector under specified conditions. |
| chromatogram/krəʊˈmætəɡræm/ | chromatogram |
| mass spectrometer/mæs spekˈtrɒmɪtə/ | mass spectrometer |
Separating a vapour
- Gas/liquid chromatography (GLC) separates a mixture of volatile components.
- The mobile phase is a carrier gas 载气; the stationary phase is a liquid on a solid.
- Each component leaves a peak at its own retention time 保留时间.
Gas/liquid chromatography route
Follow a volatile sample through column separation to a chromatogram.
In gas chromatography, the time a component takes to pass through the column is its ______ time.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Used to identify components.
Gas chromatography separates a mixture of volatile substances.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
They travel through the column at different speeds.
How it works
- the stationary phase is a high-boiling-point non-polar liquid on a solid support.
- the mobile phase is an unreactive carrier gas (e.g. nitrogen).
- the retention time is how long a component takes to pass through.
- A component that interacts more with the stationary phase has a longer retention time.
A gas-liquid chromatogram 色谱图 with retention times and peak areas
In GLC, the mobile phase is:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
A carrier gas moves the components past the liquid stationary phase.
A component that interacts more strongly with the stationary phase has a:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
More interaction slows it down, so it takes longer to pass through (longer retention time).
Reading the chromatogram
- The area of each peak gives the proportion of that component in the mixture.
A chromatogram shows two peaks with areas in the ratio 3 : 1.
- Total = 3 + 1 = 4 parts.
- So the mixture is 75% of the first component and 25% of the second.
(Peak height can mislead — always use the area.)
The area of each peak in a chromatogram gives:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Peak area is proportional to the amount, so it gives the percentage composition.
Identifying the components
- A peak's retention time matches a known standard run in the same conditions → that names the component.
- Coupling GLC to a mass spectrometer 质谱仪 (GC–MS) confirms each component's identity from its mass spectrum.
- GC–MS is the workhorse of forensics, drug testing and airport security.
You've got it
- GLC: mobile phase = carrier gas; stationary phase = a non-polar liquid on a solid
- each component has a retention time; more interaction → longer retention
- the peak area = the proportion of that component (areas 3:1 → 75% : 25%)
- match retention time to a standard to identify; GC–MS confirms it