positive or negative ion

From a quick google search, it appears that hydroquinone may be detectable through LC/MS (ESI) in both positive and negative mode. It forms a protonated molecule ([M+H]+) at m/z 111 in positive mode and two ions at m/z 108 and 109 in negative mode. 

http://www.t3db.ca/toxins/T3D4577

I would recommend looking up some peer reviewed journal articles to gain more information on the specific parameters needed to detect these compounds through LC/MS.