It's tricky;
akin to trying to describe facial recognition or fingerprint matching in words.

In earlier days using GC-FID, one only got a straight chromatogram of all hydrocarbons in the sample,
and had to compare this profile against those to standards of commercially-available ignitable liquids;
one would need to match the unknown's profile (a sequence of chromatographic peaks of comparable height and retention time)
to a recognizable profile of ILR-compounds in the standard (even if the unknown's profile is a bit beaten up due to 'weathering').


For the past few decades, using GC-MS arson chemists have been able to use extracted-ion chromatograms
to draw out the target ILR-compounds from under the chromatogram's matrix background;
whilst a great tool, it allows you to see stuff out of context.


ASTM E1618 promotes extracted-ion chromatograms to identify certain target compounds, then lists target compound (groups) to be identified in respective ILR's.

Call me old-school, but as a confirmation, I'd at least also like to so a recognizable IRL-profile of ILR-compounds
in the respective groups of extracted-ion chromatograms before signing it off as positive.
(i.e. a bit like needing to recognize a face, however 'weathered', instead of just relying on a match of a few target mathematical ratios).