Three types of zinc porphyrins have been used for the design of carbon paste or diamond paste based amperometric dot-sensors. Sildenafil citrate was determined using these sensors by employing differential pulse voltammetry. The linear concentration range for the proposed electrodes was between 10(-11) and 10(-4) mol L(-1), with the lowest detection limit (2.46 pmol (-1)) obtained using the diamond paste dot-sensor modified with zinc-5,10,15,20-tetra(4-sulfophenyl)porphyrin. Sildenafil citrate was determined reliably from its pharmaceutical formulations, namely Viagra with recovery values higher than 93%. (C) 2011 Elsevier Ltd. All rights reserved.