This research work concerns the electrochemical study of dopamine and ascorbic acid in the presence of the cationic surfactant cetyltrimethylammonium bromide. From this study is possible to note that the cetyltrimethylammonium bromide greatest influence was on the dopamine, because it disfavors both its oxidation and reduction, thereby giving a smaller heterogeneous rate constant, k(0), value than in its absence, provoking that the process tends to irreversibility. On the contrary, for the ascorbic acid case, its oxidation was favored; these effects can influence the separation of the dopamine and ascorbic acid voltammetric signals up to 453 mV. Further, the method could be optimized through differential pulse voltammetry to proceed with the analytic determination of dopamine in the presence of ascorbic acid displaying usable analytic parameters, namely: a linearity range of 0-130 mu M, a sensitivity of (6.318 +/- 0.002) mu A mM(-1), a detection limit of (11 +/- 0.1) mu M, and a quantification limit of (37 +/- 0.2) mu M, which made it possible to effect the quantification on a commercial pharmaceutical sample.