I hope, I understood qestion and that I am not wrong.
Add 2 M water solution of NaOH, water solution of formaldehyde and equimolar amount of acetone to contamined hexane. Heat the emulsion to some 50 oC and mix, or shake it carfully /amounts of CH2=O and CH3COCH3 added depend on amount of fulvene in the sample/
Cyklopentadiene /fulvene/ should undergo to condenzation reactions yielding yellow or orange colored products that are very easily to polymerize /b.p. of these moieties is much higher than that of hexane..
Separate water layer from the mixture, extract several times hexane layer with distilled water.