A carbon nanotube paste electrode modified in situ with Triton X 100 was developed for the individual and simultaneous determination of acetaminophen (ACOP) aspirin (ASA) and caffeine (CF) The electrochemical behavior of these three molecules was investigated employing cyclic voltammetry (CV) electrochemical impedance spectroscopy (EIS) chronocoulometry (CC) and adsorptive stripping differential pulse voltammetry (AdSDPV) Kramers-Kronig transformation implied that the resulting impedance data were validated and were of very good quality These studies revealed that the oxidation of ACOP ASA and CF is facilitated at an in situ surfactant-modified multiwalled carbon nanotube paste electrode (ISSM-CNT-PE) After optimization of analytical conditions employing this electrode at pH 7 0 in phosphate buffer (0 1 M) the peak currents for the three molecules were found to vary linearly with their concentrations in the range of 2 91 x 10(-7)-6 27 x 10(-5) M with detection limits of 258 x 10(-8) 8 47 x 10(-8) and 8 83 x 10-8 M for ACOP ASA and CF respectively using AdSDPV The prepared modified electrode showed several advantages such as a simple preparation method high sensitivity very low detection limits and excellent reproducibility Furthermore the proposed method was employed for the simultaneous determination of ACOP ASA and CF in pharmaceutical formulations urine and blood serum samples and the obtained results were found to be satisfactory (C) 2010 Elsevier Ltd All rights reserved