**2.1 Materials**

The commercial chemicals: luminol (Fluka), ANS (Aldrich), graphite powder (sigma), nujol (Alfa- Aesar), HCl (Fermont), HClO4 (Fermont), HNO3 (Caledón), H2SO4 (Fermont) and camphorsulfonic acid (Aldrich) were of analytical reagents grade and were used without further purification except the aniline (Sigma) which was distilled before use at stored to low temperature in the dark. The aqueous solutions were prepared using deionized water, and the solutions were deoxygenated by purging with nitrogen gas. After this, a nitrogen atmosphere was kept over the solution during each run.
