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How is retention time used to identify a substance in gas chromatography?

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What is chromatography? — chromatography Overview of the chemical technique of chromatography.

In gas chromatography, retention time is defined as the interval between the moment a sample is injected and the moment a specific component is detected at the exit of the column.1

Because retention times vary depending on the identity of a chemical component, they are used for qualitative analysis. To identify an unknown substance, chemists compare its measured retention time against the retention times of known substances analyzed under identical conditions.1

The specific retention time of a substance is determined by the strength of the intermolecular forces between the solute and the stationary phase. Solutes that are more strongly attracted to the stationary phase are held back longer, resulting in a longer retention time compared to those that interact less strongly.23