The electrochemical detection of two pharmaceuticals, propranolol (PROP) and hydrochlorothiazide (HTZ), was studied using a nitrogen-containing tetrahedral amorphous carbon (ta-C:N) electrode. Measurements were also made using a boron-doped diamond (BDD) electrode, for comparison. The ta-C:N electrode functioned well for the simultaneous determination of PROP and HTZ in artificial urine and serum by square-wave voltammetry, both of which were detected at high positive potentials. The PROP (ca. 1.2 V) and HTZ (ca. 1.4V) oxidation peak potentials were separated by about 200 mV. The respective analytical response curves presented good linearity in the investigated concentration range from 0.9 to 9.8 mu mol L-1 for PROP and from 3.0 to 9.8 mu mol L-1 for HTZ with calculated limits of detection (S/N = 3) of 0.75 mu mol L-1 (similar to 194 ng/mL) for PROP and 2.50 mu mol L-1 (similar to 744 ng/mL) for HTZ. Essentially, the lowest concentration measured voltammetrically was the LOD. The results indicate that the ta-C:N electrode could be an excellent new carbon material for electrochemically-active analytes requiring high potentials for detection. (C) 2014 Elsevier Ltd. All rights reserved.