Chromatography Forum

hello,

we have some problems identifying a component from a full scan chromatogram.
It is the small peak at 13.40 in the first chromatogram.

Using the NIST it turned out to be anthracene or phenanthrene with a match of over 900
It is not present in the blank (second chromatogram).

In order to confirm its ID I've injected a PAH-mix (3th chromatogram). (Peak shape is bad because the concentration is to high.)
the peaks at 14.22 and 14.39 are anthracene and phenanthrene but these are +/- 1 minute later than our unknown that has been identified as anthracene by NIST.

to make sure there wasn't a problem with flow etc I've made a mix of both the unknown and the PAH-mix and this produced chromatogram 4.
You can clearly see al 3 peaks (the peak at 13.96 is irrelevant to this problem) and they have stayed at their retention time.

comparing the mass-spectra of peak 13.40 and 14.22 gives the spectra below. They are identical !!!

so the question is:
can the small peak at 13.40 be Anthracene
if not : what is it ??

Diphenylene, or Benz[a]azulene perhaps (these are just other choices from a library search of anthracene). Many of the less common PAHs will show up in a sample with lots of the traditional priority pollutant PAHs. The library is not very good at distinctions among the PAH isomers. The RT shift makes it clear it is not the usual suspects.

Benz[a]azulene might be possible. For Diphenylene the MW of 152 doesn't match the 178 from the mass-spectra.
thanks for your help