You are going to find it very difficult to isolate PAHs from a UCM unless the UCM itself is not derived from any aromatic compunds (which is unlikely). The UCM will comprise of a wide range of compounds some of which will be aromatic in nature. Therefore, whatever processes you use to isolate the PAHs will also isolate the other aromatic compunds contributing to the UCM. You can reduce the complexity of the UCM by isolating an aromatic fraction (using a standard SARA separation approach) which contain your target PAHs and any other aromatic material present. I think this is the best you can hope to achieve.

If you have large sample extract and you are looking for an easy method, I would suggest yoy DMF:pentane partitioning (Mandalakis et al., 2004. Efficient isolation of polyaromatic fraction from aliphatic compounds in complex extracts using dimethylformamide-pentane partitionings. Journal of Chromatography A, 1041, 1-2, 111-117.

By using this method, you can easily remove the aliphatic part of UCM and, at least, a large part of the monoaromatic fraction. It's worth to try.

I agree with Manolis. We have found that you can substitute DMSO for the DMF and achieve good results as well. You will extract other aromatics, but assuming that you are using GC-MS as your analytical method you should see a great increase in detectability.

We've also done some aliphatic/aromatic fractionation using silver-coated alumina (Supelco). We've had good results for the heavier polyaromatics, but recovery of the light end naphthalenes has been a bit disappointing.

Andy Booth's answer is correct from my perpsective.While many people think of the UCMin a gas chromatogram as being an alkane/cycloalkane complex mixture phenomena for petroleum and petroleum contaminated samples, the aromatic fraction from such samples often also contains a GC UCM .I believe that the most effective approach to the challenge of quantitaive and qualitiative individual compund analyses in this circumstance is two dimensional GC coupled with MS after the usual column, Thin layer or HPLC separations. However, the challenge with that approach(2xGC) is the lack of standards for individual compound verification in an absolute sense. However, estimates based on GC and surrogate calibration compunds are better than nothing at all.

John is absolutely right about GCxGC-MS. I guess the main question we should ask you is why you want to isolate the PAHs in the first place? GCxGC allows you to separate components in the UCM chromatographically so you can get accurate quatification (as long as you have suitable standards or surrogates).

Thanks to you all for your answers.

I'm actually harvesting PAHs with a PcGC for further compound specific isotope analysis.

And i need a sufficiently clean baseline to avoid RT shifts on my PcGC inducing loss of PAHs and harvesting of interfering adjacent compounds. That's why i wanted to know how a UCM can be reduced. I think i'm gonna go with a rough harvesting with wider RT windows and than refine this by a secondary harvesting on the PcGC.