Black Pearls (BP) carbon powder was chemically modified with chloroanthraquinone groups by spontaneous reduction of 1-amino, 5-chloroanthraquinone with the aim of determining the quinone content of the modified carbon. This information is essential to determine the increase of capacitance associated to the grafted quinone molecules. The capacitance of pristine carbon electrode was doubled due to the presence of the grafted electroactive molecules. The modified BP powder was characterized by thermogravimetric and elemental analyses. The modified powder was also used to fabricate composite electrodes that were characterized by electrochemistry to determine the loading of electroactive quinone molecules. The presence of the chlorine atom on the anthraquinone moiety allows an estimation of the loading from elemental analysis, which is in relatively good agreement with the value estimated by electrochemistry.