In this work, direct insertion probe pyrolysis mass spectrometry technique was applied to investigate the thermal and the structural characteristics of electrochemically prepared HCl and HNO3-doped polyaniline (PANI) films. It has been determined that the thermal degradation of both samples showed three main thermal degradation stages. The first stage around 50-60 degrees C was associated with evolution of solvent and low-molecular-weight species adsorbed on the polymer, the second stage just above 150 degrees C was attributed to evolution of dopant-based products, and the final degradation stage at moderate and elevated temperatures was associated with evolution of degradation products of the polymer. Chlorination and nitrolysis of aniline during the electrochemical polymerization were detected. Extent of substitution increased as the electrolysis period was increased. Furthermore, for the HNO3-doped PANI, the evolution of CO2 at elevated temperatures confirmed oxidation of the polymer film during electrolysis. (C) 2007 Wiley Periodicals, Inc.