9 Gas chromatography in practice continued

Figure 6 shows an example of a chromatogram for a range of different pesticides. Each pesticide is shown as an individual peak with different retention time.

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Figure 6 Example chromatogram © The Open University
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The chromatagram shows a number of pesticides, represented by individual peaks at different retention times. Sixteen peaks in total are shown and are distributed along the X-axis. Annotation: The X-axis is labelled retention time/minutes, and values range from zero to sixteen by increments of one minute. The Y-axis is labelled dectector response by percent. The Y-axis values are arranged as four percent increments and range from zero to one hundred. The values twenty, forty, sixty eighty and one hundred are labelled.

Figure 6 Example chromatogram © The Open University

How could retention time be used to identify the pesticides in a mixture?

Answer

Standards containing the different pesticides could be used to determine the retention times of particular pesticides, which can then be compared to the retention time of the peaks in the sample.

Although the retention time of a particular compound can be matched against that of a standard, the differences in retention time between different compounds can be small. Chromatography combined with mass spectrometry (GC–MS) is often used to conclusively identify a substance.

8 Gas chromatography in practice

10 Mass spectroscopy