This work presents the optimization process of mercury determination by Anodic Stripping Voltammetry (ASV), using a glassy carbon modified with a gold film as working electrode, in samples extracted by aqua regia.The samples may contain Cu, Fe or Pb in high concentrations.In these conditions the usual Hg determination by ASV is almost impossible.The effects of the supporting electrolyte on the sensitivity of the method and chloride and nitrate ions concentration were studied.Supporting electrolyte was selected between: HCl, HNO 3 , HClO 4 and CH 3 COOH.Our results show that the best sensibility is obtained with HClO 4 0.10 M. High chloride concentration decreases the useful potential window and the peak current.However, small chloride additions are required to obtain high peak currents because chloride prevents Au film poisoning.Another interference studied was that of Cu and Fe.This kind of interference can be avoided if the sample in the electrochemical cell is exchanged for fresh electrolytic solution (HCl 0.01 M -HClO 4 0.10 M) before the stripping step.