Explain4 marksStandard
A mixture of three alkanes (pentane, hexane, heptane) is analysed by gas-liquid chromatography using a non-polar stationary phase (a high boiling point alkane on a solid support) and nitrogen as the mobile phase. The chromatogram shows three peaks with the following retention times and peak areas:
| Peak | Retention time / min | Peak area (arbitrary units) |
|---|---|---|
| A | 2.1 | 120 |
| B | 3.5 | 80 |
| C | 5.8 | 200 |
(a) Explain why the three alkanes have different retention times. In your answer, refer to the interaction between each alkane and the stationary phase.
(b) Describe how the percentage composition of the mixture can be determined from the chromatogram.
(c) Identify which peak (A, B or C) corresponds to pentane. Explain your reasoning.