[DeadliestNoodle]

When running a GC/MS with heptane, octane, dodecane, 2,2,4-trimethylpentane, and 4-heptanone, with nonane being an internal standard, I only receive 3 peaks for my gas chromatogram (a clear nonane peak and dodecane peak are present), but one of the peaks is a mixture of three substances and heptane is missing. I understand that the octane, 2,2,4-trimethylpentane, and 4-heptanone all exhibit about the same mass. but how would I figure out the composition of an unknown if three components are mixed in with each other?

[marquis]

There are several ways, most with method changes.  One involves changing your column.  Save that for last.  The other involves changing your method.  I don't know what your temp conditions are, but change them so that there is more time at the temp where the three peaks come out.  You may be able to separate them that way.

  Lastly, your data system maybe able to separate each individual molecule by doing a selective ion separation.  That takes looking at the mass spectra of each molecule, though.
That is the easiest way to approach the situation.

Good luck.