It seems that the hard work in the last week paid off. After a good look into my data I have decided to make some (rather simple, but nevertheless effective) changes to my method:
* I have increased the sample size by a factor of 6
* I have increased the adsorption time from 40 min to 120 min
The latter had only a minor effect on the results (so I will stick with the shorter adsorption time), but the increase in sample size did the trick. The tiny peaks with only a very small number of fragments for some aromatic compounds are now clearly separated from the noise and the underlying mass spectrum passes my and the NIST library search.
I have analysed samples from the McGill campus lawn and from a site at the McGill Research Station in Mont Saint Hilaire (east of Montreal) and the main compound groups that are have detected were aromatic compounds (toluene, xylenes, benzaldehyde), aldehydes and some aliphatic alcohols.
However, I am still wondering, if halogenated compounds a present (no ever so small isotope signatures from chlorine or bromine so far) and it seems that benzene is still buried in the water peak at the beginning of the run (although I have modified my method so that it elutes later in a less contaminated section of the chromatogram – this works fine for toluene, but not for benzene). Another explanation, of course, is that these compounds are not present or only at very low levels. Well, there is more to look at.
