Oil and grease extraction and aromatics BG

At the forum of the Bioremediation Discussion group

Question Nicole Merkl:
I do total oil and grease (TOG) extraction with methylene chloride. Does
anybody know which fraction is extracted last? E.g. is it true that the
aromatics get extracted rather late and their content in the final sample
can therefore be influenced by extraction time? Can you recommend any
literature concerning this point?

Answer:
what is the intent to do the extraction - determination of total oil and
grease?
In this case it is not clear, why to worry about the aromatics. They would
normally constitute only a minor part of the whole extracted fraction, that
means in between the limits of error.
If the intent is to gain a fraction for further analysis, then the targeted
compounds are essential for evaluation of the extraction behaviour.
The order of extraction will depend further on the interactions with the
matrix (aromatics sorbed at a clay might desorb later, aromatics
partitioned into oil will not).
The chance of desorbing later is greater for PAH, and the 'unresolved
hydrocarbon fraction in the GC' than for alkylbenzenes and 'normal'
hydrocarbons.

Any comments?