The dependence of the peak area, Q, on the analyte volumetric flow rate, U, in flow injection analysis (FIA) and high performance liquid chromatography (HPLC) with amperometric detection, was studied for typical electroactive species and in a wide flow rate range. Based on the hydrodynamics of thin channel flow cells (as established by steady state experiments) and simple dispersion theory considerations, a linear relationship between log Q and log U with a -2/3 slope has been derived in a general manner (irrespective to the type of dispersion) for amperometric detectors operated in the limiting current potential region. In the case of mixed mass transfer and kinetic control the variation of Q with U is more complicated but the peak area is still smoothly decreasing with the flow rate. These predictions were found to be in reasonable agreement with experiment for a few indicative systems both in FIA and HPLC experiments. On the contrary, the non-steady state current corresponding to the peak maximum of FIA and HPLC exhibited local maxima and the former could not be described by any of the equations proposed for the dispersion in FIA experiments. The practical implications of the form of integrated signal, Q, dependence on flow rate for FIA and HPLC amperometric detection are also discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.