Being unknown, I would never use the nearest compounds respond factors. However, a general answer cannot be given. It depends on the used detector. For example the FID can be viewed as a carbon atom (CH2) counter, whose response is proportional to the carbon content of the peak material being analyzed. However the cell design, the physics of the ion stream in the hydrogen flame and the molecular structure and composition of the peak compound will affect the response. The EPA has published some “FLAME IONIZATION DETECTOR RESPONSE FACTORS”. In case the detector is based on plasma emission spectroscopy (former HP AED detector) you can have more than one chromatogram for every element you want to measure: C, H, N, S, N, Halogens – Channel. The response of such a detector does no longer depend on the molecular structure. One calibration standard containing the atom of interest is sufficient to calibrate the whole chromatogram. With such a detector you even will get the sum formula and quantitative results even for unknown compounds. This cannot be achieved by other detectors. Our paper (see below) describes a self-build AED detector viewing axially on the plasma and using porcelain plasma tubes to overcome the small drawbacks of the HP instrument (no longer produced). Due to its non-complete pyrolysis some molecular structure effects were still present.

In addition to the comment of Karl: If you are using a TCD as detector you might get an idea of the amount when using some "average thermal conductivity". Most gases do not differ that much. Every processing software calculates "area %" and with a TCD you get quite often a reasonable guess of your amount without calibration.

Anyhow, the question remains why you want to quantify an unknown peak :-)

If you have all other peaks correctly identified (e.g. in a hydrocarbon mixture) and properly calibrated the amount of yourunknown peak is usually 100-Sum(all others) :-)

Stefan