The line shape of a peak on a chromatogram can offer some insight into the presence of a functional group. However, issues with the instrument are also known to affect the line shape for a peak.
The GC/MS EI+ Total Ion Chromatogram/Current (TIC) below shows five peaks. All of the peaks with the exception of the peak at 1.8 minutes exhibit a symmetrical line shape. The asymmetry of the peak at 1.8 minutes is typical for a structure containing an acidic group (i.e. -COOH).
The peak at 1.8 minutes is 2-ethylhexanoic acid.