Dear Sir. Concerning your issue about the the possibilities for detection of phenol, benzoquinone, hydroquinone and chlorophenol in LC-ESI/MS . These compounds can be detected by LC-ESI/MS. I think the following below links may help you in your analysis:

http://pubs.acs.org/doi/abs/10.1021/es981045r?src=recsys&journalCode=esthag

http://worldwidescience.org/topicpages/h/hydroquinone+p-benzoquinone+phenol.html

http://las.utalca.cl/RCMS2006.pdf

Thanks

Yes, they are all candidates for ESI ionization. Note that you may be better in negative ion for chlorophenol.

They should all ionize under APCI conditions as well, if you also have APCI.