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10 Quantification of electroinactive dopants in conductive polypyrrole (PPY) films was performed with electrochemistry combined on-line with inductively coupled plasma-atomic emission spectrometry (EC/ICP-AES). Anion (HSO4−) ejection out of a PPY film was first chosen as a model system and the results obtained with EC/ICP-AES were found to be comparable with values deduced by electrochemical quartz crystal microbalance (EQCM). The EC/ICP-AES approach was then extended to cases where EQCM findings become difficult to interpret (i.e. simultaneous insertion of Na+ into and ejection of HSO4− out of PPY film). It is demonstrated that EC/ICP-AES can simultaneously quantify both cationic and anionic species involved in the PPY redox switching. This is in contrast with EQCM studies that can only detect the net mass change from the two competing processes. This study shows that EC/ICP-AES is a viable technique for providing accurate information concerning the doping/dedoping processes without the necessity of removing the polymer-modified electrode from the electrochemical flow cell. More importantly, the species investigated do not need to be electroactive. It is clear that the comparative study between the two techniques can be powerful in unraveling relatively complicated redox reactions and ion-transport processes in conductive polymer films. © 2001 Published by Elsevier Science B.V. 11