Tailing Peaks

Tailing Peaks

Peak tailing is one of the more common changes in peak shape. If left undealt with, it can lead to reduced accuracy in peak integration and loss of resolution between closely eluting peaks. If the sample is being introduced via a manual injection, peak tailing can be a result of uneven injection speed. This can be resolved by depressing the syringe plunger in one smooth movement, reducing the sample volume or using an autosampler. But if you’re already using an autosampler, then it is likely that there’s something physically wrong with the system. This commonly happens if maintenance is required or has not been performed correctly.

Here are some things to check:

- If you haven’t done so already, look for leaks in the system – check all connections, and replace the septum and seals if they are damaged.

- Then consider whether the column has been installed correctly. Reinstall the column to the correct depth to avoid dead-volume issues and verify that the column has a clean ‘square’ cut at both ends.

- Another possibility is that you have adsorption on the column or liner due to surface activity or contamination. Check the liner for contamination and replace with a clean, deactivated one if necessary. Try trimming 1–3 inches off the inlet end of the column and reinstalling it. If the peak shape does not improve, then bake out the column following the manufacturer’s instructions or replace it.

Over time, a GC inlet septum will become ‘cored’ due to the insertion of the needle.
A septum damaged in this way is the cause of many troubleshooting issues, and septa are in fact one of the most commonly replaced GC consumables.

Example of clean, undamaged septa

Liners typically contain silica (glass) wool to aid with injection, but over time these can turn black because of contamination
– a sure sign that they need to be replaced (3 liners from the left are dirty).

A straight, 'square' cut at the end of the column is required to ensure good chromatography.
Try to avoid having a jagged edge or cutting at an angle, as this can have an adverse effect on the chromatography and retention reproducibility.

If tailing is only affecting certain peaks, then this suggests a problem with method parameters. Acids, amines and other compounds containing strongly polar or reactive functional groups are commonly prone to adsorption and tailing, in which case changing the column phase should be considered. Failing that, you might need to incorporate a derivatisation step, such as methylation, into your sample prep protocol.

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