The influence of the model surfactant Triton-X-100 on the electroanalysis of trace lead and cadmium ions by anodic stripping voltammetry at Nafion-coated carbon film electrodes has been studied by electrochemical impedance spectroscopy. Spectra were recorded before and after metal deposition, without and with the presence of surfactant. Plots of the imaginary part of the impedance vs. the logarithm of the frequency are shown to be particularly useful for diagnostic purposes. Results demonstrate that the effect of Triton is greatest below its critical micelle concentration and particularly at low concentrations below 100 mg dm(-3), the blocking of the electrode surface being reversible in these cases. Permanent changes to the structure and morphology of the Nation film are normally less than in the absence of surfactant. Comparison with square wave stripping voltammetry data at Nafion-coated mercury thin film electrodes shows that the results obtained in this study are also applicable at such electrodes. (c) 2006 Elsevier B.V. All rights reserved.