Retention Times

AQA A-level ChemistryChromatographyLesson 6 of 7

In gas chromatography, the retention time of a substance is the time taken from injection of the sample to that substance reaching the detector. It is read from the chromatogram as the time at the top of the substance's peak.

Under fixed conditions, each substance has a characteristic retention time. It depends on:
• how strongly the substance interacts with, or dissolves in, the stationary phase
• its volatility (boiling point)
• the conditions: column type and length, oven temperature and carrier gas flow rate.

So, to identify a component, compare its retention time with those of known substances run on the same machine under the same conditions. Different substances can have similar retention times, so this alone does not always give a certain identification.

More in Chromatography

• Chromatography
• Thin-Layer Chromatography
• Rf Values
• Column Chromatography
• Gas Chromatography
• Combining Chromatography with Mass Spectrometry

All 7 lessons in Chromatography · All AQA A-level Chemistry topics