Full equations of convective diffusion are solved numerically for a strip-like (2D) electrodiffusion friction probe in a stream of microdisperse liquid, assuming a non-linear near-to-wall velocity profile ranging from simple shear flow (p = 1) to ideal slip (p = 0). The range of generalized Peclet number H from H = 0 01 (almost pure spatial diffusion) to H = 100 (diffusion layer with negligible longitudinal diffusion) covers all cases of possible experimental relevance The main result is expressed as a relative deviation of actual total diffusion flux N from its diffusion-layer approximation N-DLA,N- Psi = N/NDLA - 1. (C) 2010 Elsevier Ltd. All rights reserved.