Why are my GC peaks tailing?

Peak tailing is when the back edge of a peak falls off more slowly than the front edge rises, producing a tail that drags to the right. Tailing reduces resolution between adjacent peaks and affects quantification accuracy.

Active sites in the flow path

The most common cause. Metal surfaces, contaminated liners, and degraded septa can contain active sites that interact with polar or reactive compounds. The compound adsorbs briefly onto the active surface and then desorbs slowly, producing a tail.

To fix this, replace the liner. Check that all connections use deactivated or inert components. Use deactivated liners and guard columns where appropriate.

Cold spots in the flow path

If any part of the sample path between the injector and the detector is cooler than it should be, compounds can condense briefly and then re-evaporate slowly. This produces tailing. Check that the injector and detector temperatures are set high enough for the compounds being analysed. Check that transfer lines are properly heated.

Column degradation

As a column ages, the stationary phase near the inlet end degrades first, creating active sites that cause tailing. Trimming a short length (0.5 to 1 m) from the inlet end of the column can restore peak shape if degradation is the cause.

Too slow a detector response

If the detector electronics or data acquisition rate are too slow relative to the peak width, the recorded peak shape will show artificial tailing. This is more relevant in fast or ultra-fast GC where peak widths are very narrow.

How to diagnose

If tailing affects all compounds, look at the liner, connections, and flow path first. If it affects only specific polar or reactive compounds, active sites are the most likely cause. If it appeared suddenly after a maintenance event, check for contamination introduced during the work.