This conversion of HQ into BQ was taken as the basis for ultra-trace determination of HQ in aqueous solutions where the formation of yellowish solution is responsible for absorption in UV region due to catalytic oxidation of the HQ into BQ by KMnO4. In other words the HQ is determined at the cost of BQ formation. The formation of yellow colored solution is the indication of BQ formation. Moreover, the conversion of HQ into BQ brings structural changes from benzenoid to quinoid ring according to chromophore theory [20]. HQ has also been determined by HPLC in air as BQ after oxidation on a permanganate-impregnated glass–fiber filter, trapping BQ on an XAD-2 adsorbent and desorbing it with acetonitrile