A carbon paste electrode modified with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was used to carry out an electrochemical study at pH 3 in 0.1 M NaCl by differential pulse voltammetry to discern the effect of the surfactant on the electrochemical signals of adrenaline (AD) and ascorbic acid (AA). It was shown that in the absence of CTAB, AA and AD voltammetric signals overlap in the 500-600 mV potential interval. However, in the presence of CTAB, the AD oxidation process was not favored, whereas the opposite is true for the AA, which leads to an effective peak separation. This method permitted to obtain reliable analytical parameters to undertake the determination of AD in the presence of AA as the detection limit was 7.20 +/- 0.04 mu M, the quantification limit was 24.32 +/- 0.08 mu M, the sensitivity was 2.478 +/- 0.067 mu A mM(-1), and the linearity range was 0.01-0.27 mM. This approach was used effectively to determine AD in real pharmaceuticals obtaining satisfactory results. Moreover, it is shown that the simultaneous determination of AD and AA may be performed and that AD can be adequately determined even in the presence of both AA and uric acid. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3223664] All rights reserved.